  Linux IP Masquerade HOWTO
  David Ranch, dranch@trinnet.net
  v1.85, May 29, 2000

  This document describes how to enable the Linux IP Masquerade feature
  on a given Linux host.  IP Masq is a form of Network Address Transla­
  tion or NAT that allows internally connected computers that do not
  have one or more registered Internet IP addresses to have the ability
  to communicate to the Internet via your Linux box's single Internet IP
  address.
  ______________________________________________________________________

  Table of Contents



  1. Introduction

     1.1 Introduction to IP Masquerading or IP MASQ for short
     1.2 Foreword, Feedback & Credits
     1.3 Copyright & Disclaimer

  2. Background Knowledge

     2.1 What is IP Masquerade?
     2.2 Current Status
     2.3 Who Can Benefit From IP Masquerade?
     2.4 Who Doesn't Need IP Masquerade?
     2.5 How does IP Masquerade Work?
     2.6 Requirements for IP Masquerade on Linux 2.0.x
     2.7 Requirements for IP Masquerade on Linux 2.2.x
     2.8 Requirements for IP Masquerade on Linux 2.3.x and 2.4.x

  3. Setting Up IP Masquerade

     3.1 Compiling the Kernel for IP Masquerade Support
        3.1.1 Linux 2.2.x Kernels
        3.1.2 Linux 2.0.x Kernels
        3.1.3 Linux 2.3.x / 2.4.x Kernels
     3.2 Assigning Private Network IP Addresses to the Internal LAN
     3.3 Configuring IP Forwarding Policies
        3.3.1 Linux 2.0.x Kernels
        3.3.2 Linux 2.2.x Kernels

  4. Configuring the other internal to-be MASQed machines

     4.1 Configuring Microsoft Windows 95
     4.2 Configuring Windows NT
     4.3 Configuring Windows for Workgroup 3.11
     4.4 Configuring UNIX Based Systems
     4.5 Configuring DOS using NCSA Telnet package
     4.6 Configuring MacOS Based System Running MacTCP
     4.7 Configuring MacOS Based System Running Open Transport
     4.8 Configuring Novell network using DNS
     4.9 Configuring OS/2 Warp
     4.10 Configuring OS/400 on a IBM AS/400
     4.11 Configuring Other Systems

  5. Testing IP Masquerade

  6. Other IP Masquerade Issues and Software Support

     6.1 Problems with IP Masquerade
     6.2 Incoming services
     6.3 Supported Client Software and Other Setup Notes
        6.3.1 Network Clients that -Work- with IP Masquerade
        6.3.2 Clients that do not have full support in IP MASQ:
     6.4 Stronger IP Firewall (IPFWADM) Rulesets
     6.5 Stronger IP Firewall (IPCHAINS) rulesets
     6.6 IP Masquerading multiple internal networks
     6.7 IP Masquerade and Dial-on-Demand Connections
     6.8 IPPORTFW, IPMASQADM, IPAUTOFW, REDIR, UDPRED, and other Port Forwarding tools
        6.8.1 IPPORTFW on 2.0.x kernels
        6.8.2 IPMASQADM with IPPORTFW support on 2.2.x kernels
     6.9 CU-SeeMe and Linux IP-Masquerade
     6.10 Mirabilis ICQ
     6.11 Gamers:  The LooseUDP patch

  7. Frequently Asked Questions

     7.1 What Linux Distributions support IP Masquerading out of the box?
     7.2 What are the minimum hardware requirements and any limitations for IP Masquerade?  How well does it perform?
     7.3 I've checked all my configurations, I still can't get IP Masquerade to work.  What should I do?
     7.4 How do I join or view the IP Masquerade and/or IP Masqurade Developers mailing lists and archives?
     7.5 How does IP Masquerade differ from Proxy or NAT services?
     7.6 Are there any GUI firewall creation/management tools?
     7.7 Does IP Masquerade work with dynamically assigned IP addresses?
     7.8 Can I use a cable modem (both bi-directional and with modem returns), DSL, satellite link, etc. to connect to the Internet and use IP Masquerade?
     7.9 Can I use Diald or the Dial-on-Demand feature of PPPd with IP MASQ?
     7.10 What applications are supported with IP Masquerade?
     7.11 How can I get IP Masquerade running on Redhat, Debian, Slackware, etc.?
     7.12 TELNET connections seem to break if I don't use them often.  Why is that?
     7.13 When my Internet connection first comes up, nothing works.  If I try again, everything then works fine.  Why is this?
     7.14 IP MASQ seems to be working fine but some sites don't work.  This usually happens with WWW and FTP.
     7.15 MASQed FTP clients don't work.
     7.16 IP Masquerading seems slow
     7.17 Now that I have IP Masquerading up, I'm getting all sorts of weird notices and errors in the SYSLOG log files.  How do I read the IPFWADM/IPCHAINS firewall errors?
     7.18 Can I configure IP MASQ to allow Internet users to directly contact internal MASQed servers?
     7.19 I'm getting "kernel: ip_masq_new(proto=UDP): no free ports." in my SYSLOG files.  Whats up?
     7.20 I'm getting "ipfwadm: setsockopt failed: Protocol not available" when I try to use IPPORTFW!
     7.21 Microsoft File and Print Sharing and Microsoft Domain clients (SAMBA) don't work through IP Masq!
     7.22 IRC won't work properly for MASQed IRC users.  Why?
     7.23 mIRC doesn't work with DCC Sends
     7.24 Can IP Masquerade work with only ONE Ethernet network card (IP Aliasing)?
     7.25 I'm trying to use the NETSTAT command to show my Masqueraded connections but its not working
     7.26 I would like to get Microsoft PPTP (GRE tunnels) and/or IPSEC (Linux SWAN) tunnels running through IP MASQ
     7.27 I want to get the XYZ network game to work through IP MASQ but it won't work.  Help!
     7.28 IP MASQ works fine for a while but then it stops working.  A reboot seems to fix this for a while.  Why?
     7.29 Internal MASQed computers cannot send SMTP or POP-3 mail!
     7.30 I need different internal MASQed networks to exit on different external IP addresses (IPROUTE2)
     7.31 Why do the new 2.1.x and 2.2.x kernels use IPCHAINS instead of IPFWADM?
     7.32 I've just upgraded to the 2.2.x kernels, why isn't IP Masquerade working?
     7.33 I've just upgraded to a 2.0.38+ kernels later, why isn't IP Masquerade working?
     7.34 I need help with EQL connections and IP Masq
     7.35 I can't get IP Masquerade to work!  What options do I have for Windows Platforms?
     7.36 I want to help on IP Masquerade development.  What can I do?
     7.37 Where can I find more information on IP Masquerade?
     7.38 I want to translate this HOWTO to another language, what should I do?
     7.39 This HOWTO seems out of date, are you still maintaining it?  Can you include more information on ...?  Are there any plans for making this better?
     7.40 I got IP Masquerade working, it's great!  I want to thank you guys, what can I do?

  8. Miscellaneous

     8.1 Useful Resources
     8.2 Linux IP Masquerade Resource
     8.3 Thanks to the following people..
     8.4 Reference
     8.5 Changes


  ______________________________________________________________________

  1.  Introduction


  1.1.  Introduction to IP Masquerading or IP MASQ for short


  This document describes how to enable the Linux IP Masquerade feature
  on a given Linux host.  IP Masq is a form of Network Address
  Translation or NAT that allows internally connected computers that do
  not have one or more registered Internet IP addresses to have the
  ability to communicate to the Internet via your Linux box's single
  Internet IP address.  It is possible to connect your internal machines
  to the Linux host with LAN technologies like Ethernet, TokenRing,
  FDDI, as well as other kinds of connections such as dialup PPP or SLIP
  links. This document uses Ethernet for the primary example since it is
  the most common scenario.
       This document is intended for users using either of the sta­
       ble Linux kernels: 2.0.38+ and 2.2.15+ on a IBM-compatible
       PC. Older kernels such as 1.2.x, 1.3.x, and 2.1.x are NOT
       covered in this document and, in some kernel versions, can
       be considered broken.  Please upgrade to one of the stable
       Linux kernels before using IP Masquerading.  The new 2.3 and
       2.4 kernels with the new NetFilter code aren't covered yet
       but URLs are provided below.  Once the feature set for Net­
       filter is final, the new code will be covered in this HOWTO.

       If you are configuring IP Masq for use on a Macintosh,
       please email Taro Fukunaga, tarozax@earthlink.net for a copy
       of his short MkLinux version of this HOWTO.



  1.2.  Foreword, Feedback & Credits

  As a new user, I found it very confusing to setup IP masquerade on
  Linux kernel, (1.2.x kernel back then).  Although there is a FAQ and a
  mailing list, there was no document that was dedicated to it.  There
  were also some requests on the mailing list for such a HOWTO.  So, I
  decided to write this HOWTO as a starting point for new users and
  possibly create a building block for other knowledgeable users to use
  add to in the future.  If you have any ideas for this document,
  corrections, etc., feel free to tell us so that we can make it better.

  This document was originally based on the original FAQ by Ken Eves and
  numerous helpful messages from the IP Masquerade mailing list.  A
  special thanks to Mr. Matthew Driver whose mailing list message
  inspired me to set up IP Masquerade and eventually writing this.
  Recently, David Ranch re-wrote the HOWTO and added a substantial
  number of sections to the HOWTO to make this document as complete as
  possible.

  Please feel free to send any feedback or comments to
  ambrose@writeme.com and dranch@trinnet.net if you have any corrections
  or if any information/URLs/etc. is missing. Your invaluable feedback
  will certainly influence the future of this HOWTO!

  This HOWTO is meant to be a fairly comprehensive guide on getting your
  Linux IP Masquerading network working in the shortest time possible.
  David is not a technical writer by trade so  you might find the
  information in this document not as general and/or objective as it
  could be.  The latest news and information regarding this HOWTO and
  other IP MASQ details can be found at the IP Masquerade Resource
  <http://ipmasq.cjb.net/> web page that we actively maintain.  If you
  have any technical questions on IP Masquerade, please join the IP
  Masquerade Mailing List instead of sending email to David.  Most MASQ
  problems are common for ALL MASQ users and can be easily solved by
  someone on the list.  In addition to this, the response time of the IP
  MASQ email list will be much faster than a reply from David.


  The latest version of this document can be found at the following
  sites which also contains HTML and postscript versions

  ˇ  http://ipmasq.cjb.net/: The IP Masquerade Resources

  ˇ  http://ipmasq2.cjb.net/: The IP Masquerade Resources MIRROR

  ˇ  The Linux Documentation Project

  ˇ  Dranch's Linux page


  ˇ  Also refer to IP Masquerade Resource Mirror Sites Listing
     <http://ipmasq.cjb.net/index.html#mirror> for other local mirror
     sites.


  1.3.  Copyright & Disclaimer


  This document is copyright(c) 2000 David Ranch and it is a FREE
  document. You may redistribute it under the terms of the GNU General
  Public License.

  The information herein this document is, to the best of David's
  knowledge, correct.  However, the Linux IP Masquerade feature is
  written by humans and thus, there is the chance that mistakes, bugs,
  etc. might happen from time to time.

  No person, group, or other body is responsible for any damage on your
  computer(s) and any other losses by using the information on this
  document. i.e.


       THE AUTHORS AND ALL MAINTAINERS ARE NOT RESPONSIBLE FOR ANY
       DAMAGES INCURRED DUE TO ACTIONS TAKEN BASED ON THE INFORMA­
       TION IN THIS DOCUMENT.


  Ok, with all this behind us... On with the show..



  2.  Background Knowledge



  2.1.  What is IP Masquerade?

  IP Masquerade is a networking function in Linux similar to one-to-many
  NAT (Network Address Translation) found in many commercial firewalls
  and network routers.  For example, if a Linux host is connected to the
  Internet via PPP, Ethernet, etc., the IP Masquerade feature allows
  other "internal" computers connected to this Linux box (via PPP,
  Ethernet, etc.) to also reach the Internet as well.  Linux IP
  Masquerading allows for this functionality even though these internal
  machines don't have an officially assigned IP addresses.

  MASQ allows a set of machines to invisibly access the Internet via the
  MASQ gateway.  To other machines on the Internet, all this outgoing
  traffic will appear to be from the IP MASQ Linux server itself.  In
  addition to the added functionality, IP Masquerade provides the
  foundation to create a VERY secure networking environment.  With a
  well built firewall, breaking the security of a well configured
  masquerading system and internal LAN should be considerably difficult.


  2.2.  Current Status

  IP Masquerade has been out for several years now and is fairly mature
  as Linux enters the 2.2.x kernel stage.  Kernels since Linux 1.3.x
  have had MASQ support built-in.  Today many individuals and commercial
  businesses are using it with excellent results.

  Common network uses like Web browsing, TELNET, FTP, PING, TRACEROUTE,
  etc. work well over IP Masquerade.  Other communications such as FTP,
  IRC, and Real Audio work well with the appropriate IP MASQ modules
  loaded.  Other network-specific programs like streaming audio (MP3s,
  True Speech, etc) work too.  Some fellow users on the mailing list
  have even had good results with video conferencing software.

  Please refer to ``'' section for a more complete listing of software
  supported.



  IP Masquerade works well as a server to other 'client machines'
  running various different OS and hardware platforms. There are
  successful cases with internal MASQed systems using :



  ˇ  Unix:  Sun Solaris, *BSD, Linux, Digital UNIX, etc.

  ˇ  Microsoft Windows 95/98, Windows NT, and Windows for Workgroups
     (with the TCP/IP package)

  ˇ  IBM OS/2

  ˇ  Apple Macintosh MacOS machines running either MacTCP or Open
     Transport

  ˇ  DOS-based systems with packet drivers and the NCSA Telnet package

  ˇ  VAXen

  ˇ  Compaq/Digital Alpha running Linux and NT

  ˇ  even Amiga computers with AmiTCP or AS225-stack.

  The list goes on and on but the point is, if your OS platform talks
  TCP/IP, it should work with IP Masquerade!


  2.3.  Who Can Benefit From IP Masquerade?


  ˇ  If you have a Linux host connected to the Internet and

  ˇ  if you have some computers running TCP/IP connected to a Linux box
     on a local subnet, and/or

  ˇ  if your Linux host has more than one modem and acts as a PPP or
     SLIP server connecting other computers, which

  ˇ  those OTHER machines do not have official or public assigned IP
     addresses (i.e. addressed with private TCP/IP numbers).

  ˇ  And of course, if you want those OTHER machines to communicate to
     the Internet without spending extra money to get additional Public
     / Official TCP/IP addresses from your ISP and either configure
     Linux to be a router or purchase an external router.


  2.4.  Who Doesn't Need IP Masquerade?


  ˇ  If your machine is a stand-alone Linux host connected to the
     Internet (though setting up a firewall is a good idea), or

  ˇ  if you already have multiple assigned public addresses for your
     OTHER machines, and


  ˇ  of course, if you don't like the idea of a 'free ride' using Linux
     and feel more comfortable using expensive commercial tools to do
     the exact same thing.


  2.5.  How does IP Masquerade Work?

  From the original IP Masquerade FAQ by Ken Eves:

    Here is a drawing of the most simple setup:

     SLIP/PPP         +------------+                         +-------------+
     to ISP provider  |  Linux     |         SLIP/PPP        | Anybox      |
    <---------- modem1|    #1      |modem2 ----------- modem3|             |
      111.222.333.444 |            |           192.168.0.100 |             |
                      +------------+                         +-------------+

      In the above drawing, a Linux box with IP_MASQUERADING is installed as
    Linux #1 and is connected to the Internet via SLIP/or/PPP using modem1.  It has
    an assigned public IP address of 111.222.333.444.  It also has modem2 connected
    to allow callers to dial-in and start a SLIP/or/PPP connection.

      The second system (which doesn't have to be running Linux) calls into the
    Linux #1 box and starts a SLIP/or/PPP connection.  It does NOT have a publicly
    assigned IP address from the Internet so it uses the private address
    192.168.0.100. (see below for more info)

      With IP Masquerade and the routing configured properly, the machine
    "Anybox" can interact with the Internet as if it was directly connected to the
    Internet (with a few small exceptions).

  Quoting Pauline Middelink:

    Do not forget to mention that the "ANYBOX" machine should have the
    Linux #1 box configured as its gateway (whether is be the default route or just
    a subnet is no matter). If the "ANYBOX" machine can not do this, the Linux
    machine should be configured to support proxy arp for all routed addresses. But,
    the setup and configuration of proxy arp is beyond the scope of the document.

  The following is an excerpt from a previous post on comp.os.linux.networking which
  has been edited to match the names used in the above example:

     o I tell machine ANYBOX that my PPP or SLIPed Linux box is its gateway.
     o When a packet comes into the Linux box from ANYBOX, it will assign it
       a new TCP/IP source port number and slap its own IP address in the packet
       header, saving the originals.  The MASQ server will then send the modified
       packet out over the SLIP/PPP interface to the Internet.
     o When a packet returns from the Internet to the Linux box, Linux examines
       if the port number is one of those ports that was assigned above.  If so, the
       MASQ server will get the original port and IP address, put them back in the
       returned packet header, and send the packet to ANYBOX.
     o The host that sent the packet will never know the difference.



  Another IP Masquerading Example:


  A typical example is given in the diagram below:



      +----------+
      |          |  Ethernet
      | A-box    |::::::
      |          |.2   : 192.168.0.x
      +----------+     :
                       :      +----------+   PPP
      +----------+     :   .1 |  Linux   |   link
      |          |     :::::::| Masq-Gate|:::::::::::::::::::// Internet
      | B-box    |::::::      |          |  111.222.333.444
      |          |.3   :      +----------+
      +----------+     :
                       :
      +----------+     :
      |          |     :
      | C-box    |::::::
      |          |.4
      +----------+

      |                       |          |
      | <-Internal Network--> |          | <- External Network ---->
      |                       |          |



  In this example, there are (4) computer systems that we are concerned
  about.   There is also presumably something on the far right that your
  PPP connection to the Internet comes through (terminal server, etc.)
  and that there is some remote host (very far off to the right of the
  page) out on the Internet that you are interested communicating with).
  The Linux system Masq-Gate is the IP Masquerading gateway for ALL the
  internal network of machines A-box, B-box and C-box to get to the
  Internet.  The internal network uses one of the several RFC-1918
  assigned private network addresses where in this case, the Class-C
  network 192.168.0.0.  The Linux box having the TCP/IP address
  192.168.0.1 while the other systems having the addresses:


  ˇ  A-Box: 192.168.0.2

  ˇ  B-Box: 192.168.0.3

  ˇ  C-Box: 192.168.0.4


  The three machines, A-box, B-box and C-box, can be running any
  operating system as long as they can speak TCP/IP.  OSes  such as
  Windows 95, Macintosh MacTCP or OpenTransport  or even another Linux
  box can connect to other machines on the Internet.  When running, the
  masquerading system or MASQ-gate converts all of these internal
  connections so that they appear to originate from masq-gate itself.
  MASQ then arranges so that data coming back in to a masqueraded
  connection is relayed back to the proper originating system.   Because
  of this, the systems on the internal network see a direct route to the
  internet and are unaware that their data is being masqueraded.  This
  is called a "Transparent" connection.

  NOTE:  Please see the ``'' for more details on topics such as:


  ˇ  The differences between NAT, MASQ, and Proxy servers.

  ˇ  How packet firewalls work



  2.6.  Requirements for IP Masquerade on Linux 2.0.x



       ** Please refer to IP Masquerade Resource
       <http://ipmasq.cjb.net/> for the latest information. **



  ˇ  Any decent computer hardware.  See the ``'' section for more
     details.


  ˇ  Kernel 2.0.x source available from http://www.kernel.org/
     (Most modern Linux ``'' such as Redhat 5.2 have modular kernels
     with all the IP Masquerade kernel options compiled in.  In such
     cases, there is no need to compile a new Linux kernel.  If you are
     UPGRADING your kernel, you should be aware of what other programs
     might be required and/or upgraded (mentioned later in the HOWTO.)


  ˇ  Loadable kernel modules, preferably 2.1.85 or newer available from
     http://www.pi.se/blox/modutils/index.html or
     ftp://ftp.ocs.com.au/pub/modutils/
     (modules-1.3.57 is the minimal requirement)


  ˇ  A running TCP/IP network or LAN covered in Linux NET-3 HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/NET-3-HOWTO.html> and the Network
     Administrator's Guide <http://metalab.unc.edu/mdw/LDP/nag/nag.html>
     Also check out the TrinityOS
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>
     deocument.  TrinityOS is a very comprehensive guide on Linux
     networking including topics like IP MASQ, security, DNS, DHCP,
     Sendmail, PPP, Diald, NFS, IPSEC-based VPNs, and performance
     sections just to name a few.  Over Fifty sections in all!


  ˇ  Connectivity to the Internet for your Linux host covered in Linux
     ISP Hookup HOWTO <http://metalab.unc.edu/mdw/HOWTO/ISP-Hookup-
     HOWTO.html>, Linux PPP HOWTO <http://metalab.unc.edu/mdw/HOWTO/PPP-
     HOWTO.html>, TrinityOS
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>, Linux
     DHCP mini-HOWTO <http://metalab.unc.edu/mdw/HOWTO/mini/DHCP.html>
     and Linux Cable Modem mini-HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/mini/Cable-Modem.html>


  ˇ  Ipfwadm 2.3 or newer available from
     ftp://ftp.xos.nl/pub/linux/ipfwadm/ipfwadm-2.3.tar.gz
     More information on version requirement is on the Linux IPFWADM
     page <http://www.xos.nl/linux/ipfwadm/>


  ˇ  If you are interested in running IPCHAINS on a 2.0.38+ kernel, see
     Willy Tarreau's IPCHAINS enabler for 2.0.36 <http://www-
     miaif.lip6.fr/willy/pub/linux-patches/> or Rusty's IPCHAINS for
     2.0.x kernels


  ˇ  Know how to configure, compile, and install a new Linux kernel as
     described in the Linux Kernel HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/Kernel-HOWTO.html>



  ˇ  You can also apply various optional IP Masquerade patches to enable
     other functionality such as:



  ˇ  TCP/IP port-forwarders or re-directors:  With these tools, you can
     get some non-MASQ friendly programs to work behind a MASQ server.
     In addition to this, you can configure a MASQ server to let
     Internet users contact internal WWW, TELNET, SMTP, FTP (with a
     patch), etc., servers.  See ``'' section of the HOWTO for more
     information.  Here is a list of IP Masquerading patches for 2.0.x
     kernels:


  ˇ  Steven Clarke's IP PortForwarding (IPPORTFW) - RECOMMENDED

  ˇ  IP AutoForward and a mirror
     <ftp://ftp.netis.com/pub/members/rlynch/ipautofw.tar.gz> (IPAUTOFW)
     - NOT Recommended

  ˇ  REDIR <http://ipmasq.cjb.net/redir_0.7.orig.tar.gz> for TCP (REDIR)
     - NOT Recommended

  ˇ  UDP redirector (UDPRED) - NOT Recommended

     PORTFWed FTP:


  ˇ  If you are going to port forward FTP traffic to an internal FTP
     server, you need to download Fred Viles's FTP server patch via HTTP
     or Fred Viles's FTP server patch via FTP.  Explicit details on this
     topic can be found in the ``'' section of the HOWTO.

     X-Windows display forwarders:

  ˇ  X-windows forwarding (DXCP)
     <ftp://sunsite.unc.edu/pub/Linux/X11/compress/dxpc-3.7.0.tar.gz>

     ICQ MASQ module

  ˇ  Andrew Deryabin's ICQ MASQ module

     PPTP (GRE) and SWAN (IPSEC) VPNs tunneling forwarders:

  ˇ  John Hardin's VPN Masquerade forwarders or the old patch for just
     PPTP Support <http://ipmasq.cjb.net/ip_masq_pptp.patch.gz>.

     Game specific patches:

  ˇ  Glenn Lamb's LooseUDP for 2.0.36+
     <ftp://ftp.netcom.com/pub/mu/mumford/loose-udp-2.0.36.patch.gz>
     patch.

     Please note that some WWW browsers with automatically uncompress
     this .gz file.  To download this file, hold down the SHIFT key as
     you click on the above URL.

     Also check out Dan Kegel's NAT Page
     <http://www.alumni.caltech.edu/~dank/peer-nat.html> for more
     information.  Additional information can be found in the ``''
     section and the ``'' section.

     Please see the IP Masquerade Resource <http://ipmasq.cjb.net/> page
     for more information available on these patches and possibly others
     as well.

  2.7.  Requirements for IP Masquerade on Linux 2.2.x



       ** Please refer to IP Masquerade Resource
       <http://ipmasq.cjb.net/> for the latest information. **



  ˇ  Kernel 2.2.x source available from http://www.kernel.org/
     NOTE #1: Linux 2.2.x kernels less than 2.2.11 have a IPCHAINS
     fragmentation bug.  Because of this, people running strong IPCHAINS
     rulesets are open to attack.  Please upgrade your kernel to a fixed
     version.

     NOTE #2: Most newer ``'' such as Redhat 5.2 might not be Linux
     2.2.x ready for your setup.  Tools like DHCP, NetUtils, etc. will
     need to be upgraded.  More details can be found in the HOWTO.


  ˇ  Loadable kernel modules, preferably 2.1.121 or newer available from
     http://www.pi.se/blox/modutils/index.html or
     ftp://ftp.ocs.com.au/pub/modutils/


  ˇ  A running TCP/IP network or LAN covered in Linux NET-3 HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/NET-3-HOWTO.html> and the Network
     Administrator's Guide <http://metalab.unc.edu/mdw/LDP/nag/nag.html>


  ˇ  Connectivity to Internet for your Linux host covered in Linux ISP
     Hookup HOWTO <http://metalab.unc.edu/mdw/HOWTO/ISP-Hookup-
     HOWTO.html>, Linux PPP HOWTO <http://metalab.unc.edu/mdw/HOWTO/PPP-
     HOWTO.html>, TrinityOS
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>, Linux
     DHCP mini-HOWTO <http://metalab.unc.edu/mdw/HOWTO/mini/DHCP.html>
     and Linux Cable Modem mini-HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/mini/Cable-Modem.html>


  ˇ  IP Chains 1.3.9 or newer available from
     http://www.rustcorp.com/linux/ipchains/
     Additional information on version requirements is at the Linux IP
     Firewalling Chains page <http://www.rustcorp.com/linux/ipchains/>


  ˇ  Know how to configure, compile, and install a new Linux kernel as
     described in the Linux Kernel HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/Kernel-HOWTO.html>


  ˇ  You can download and use various optional IP Masquerade tools to
     enable other functionality such as:


  ˇ  TCP/IP port-forwarders or re-directors:

  ˇ  IP PortForwarding (IPMASQADM) - RECOMMENDED
     <http://juanjox.kernelnotes.org/> or his old mirror.


     ICQ MASQ module

  ˇ  Andrew Deryabin's ICQ MASQ module

  Please see the IP Masquerade Resource <http://ipmasq.cjb.net/> page
  for more information available on these patches and possibly others as
  well.



  2.8.  Requirements for IP Masquerade on Linux 2.3.x and 2.4.x



       ** Please refer to IP Masquerade Resource
       <http://ipmasq.cjb.net/> for the latest information. **



  ˇ  The newest 2.3.x and 2.4.x kernels are now using a completely new
     system called NetFilter (much like the 2.2.x kernels went to
     IPCHAINS).  Many architectual changes have gone into this new code
     that will give the user a lot more flexibility, future features,
     etc.

     As of this version of the HOWTO, Netfilter is NOT covered.  Once
     the feature set of NetFilter is set, it will be decided if it will
     be added to -this- HOWTO or a new HOWTO.  Until then, please see
     the following links for the available NetFilter documentation.

     http://netfilter.kernelnotes.org/iptables-HOWTO.html and more
     specifically http://netfilter.kernelnotes.org/ipnatctl-HOWTO.html


  3.  Setting Up IP Masquerade


       If your private network contains any vital information,
       think carefully in terms of SECURITY before implementing IP
       Masquerade.  By default, IP MASQ becomes a GATEWAY for you
       to get to the Internet but it also can allow someone on the
       Internet to possibly get into your internal network.

       Once you have IP MASQ functioning, it is HIGHLY recommended
       for the user to implement a STRONG IPFWADM/IPCHAINS firewall
       ruleset.  Please see the ``'' and ``'' sections below for
       more details.



  3.1.  Compiling the Kernel for IP Masquerade Support



       If your Linux distribution already has all the required fea­
       ture support compiled such as:

       ˇ  IPFWADM/IPCHAINS

       ˇ  IP forwarding

       ˇ  IP masquerading

       ˇ  IP Firewalling

       ˇ  etc.

     and all MASQ-related modules compiled (most modular
     kernels will have all you need), then you will NOT need
     to re-compile the kernel.  If you aren't sure if you
     Linux distribution is MASQ ready, see the ``'' section or
     the IP Masquerade Resource <http://ipmasq.cjb.net/> for
     more details.  If you can't find out if your distribution
     does support IP Masquerading by default, ASSUME IT
     DOESN'T.

  Regardless of native support or not, reading this section is
  still highly recommended as it contains other useful
  information.



  3.1.1.  Linux 2.2.x Kernels


  Please see the ``'' section for any required software, patches, etc.


  ˇ  First of all, you need the kernel source for 2.2.x (preferably the
     latest kernel version 2.2.11 or above)

     NOTE #1: Linux 2.2.x kernels less than 2.2.11 have a IPCHAINS
     fragmentation bug.   Because of this, people running strong
     IPCHAINS rulesets are open to attack.  Please upgrade your kernel
     to a fixed version.

     NOTE #2: As the 2.2.x train as progressed, they keep changing the
     compile-time options.  As of this version, this section reflects
     the settings for 2.2.15.  If you are running a previous kernel
     version, the dialogs will look different.  It is recommended that
     you update to the newest kernel for all the new features and
     stability they bring.


  ˇ  If this is your first time compiling the kernel, don't be scared.
     In fact, it's rather easy and it's covered in several URLs found in
     the ``'' section.


  ˇ  Unpack the kernel source to /usr/src/ with a command: tar xvzf
     linux-2.2.x.tar.gz -C /usr/src, where the "x" in 2.2.x is the
     current Linux 2.2 kernel.  Once finished, make sure there is a
     directory or symbolic link to /usr/src/linux/


  ˇ  Apply any appropriate or optional patches to the kernel source
     code.  As of 2.2.1, IP Masq does not require any specific patching
     to get everything working.  Features like PPTP and Xwindows
     forwarders are optional.  Please refer to the ``'' section for URLs
     and the IP Masquerade Resources for up-to-date information and
     patch URLs.


  ˇ  Here are the MINIMUM options that are needed to be compiled into
     the kernel.  You will also need to configure the kernel to use your
     installed network interfaces as well.  Refer to the Linux Kernel
     HOWTO <http://metalab.unc.edu/mdw/HOWTO/Kernel-HOWTO.html> and the
     README file in the kernel source directory for further instructions
     on compiling a kernel.


     Please note the YES or NO ANSWERS to the following.  Not all
     options will be available without the proper kernel patches
     described later in this HOWTO:



    * Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]
      - YES: though not required for IP MASQ, this option allows the kernel to create the MASQ modules and enable the option for port forwarding

    -- Non-MASQ options skipped --

    * Enable loadable module support (CONFIG_MODULES) [Y/n/?]
      - YES: allows you to load kernel IP MASQ modules

    -- Non-MASQ options skipped --

    * Networking support (CONFIG_NET) [Y/n/?]
      - YES: Enables the network subsystem

    -- Non-MASQ options skipped --

    * Sysctl support (CONFIG_SYSCTL) [Y/n/?]
      - YES:  Enables the ability to enable disable options such as forwarding,
        dynamic IPs, LooseUDP, etc.

    -- Non-MASQ options skipped --

    * Packet socket (CONFIG_PACKET) [Y/m/n/?]
      - YES: Though this is OPTIONAL, this recommended feature will allow you to use TCPDUMP to debug any problems with IP MASQ

    * Kernel/User netlink socket (CONFIG_NETLINK) [Y/n/?]
      - YES: Though this is OPTIONAL, this feature will allow the logging of advanced firewall issues such as routing messages, etc

    * Routing messages (CONFIG_RTNETLINK) [Y/n/?]
      - NO:  This option does not have anything to do with packet firewall logging

    -- Non-MASQ options skipped --

    * Network firewalls (CONFIG_FIREWALL) [Y/n/?]
      - YES: Enables the kernel to be comfigured by the IPCHAINS firewall tool

    * Socket Filtering (CONFIG_FILTER) [Y/n/?]
      - OPTIONAL:  Though this doesn't have anything do with IPMASQ, if you plan
        on implimenting a DHCP server on the internal network, you WILL need this
        option.

    * Unix domain sockets (CONFIG_UNIX) [Y/m/n/?]
      - YES:  This enables the UNIX TCP/IP sockets mechanisms

    * TCP/IP networking (CONFIG_INET) [Y/n/?]
      - YES: Enables the TCP/IP protocol

    -- Non-MASQ options skipped --

    * IP: advanced router (CONFIG_IP_ADVANCED_ROUTER) [Y/n/?]
      - YES:  This will allow you to configure advanced MASQ options farther down

    * IP: policy routing (CONFIG_IP_MULTIPLE_TABLES) [N/y/?]
      - NO: Not needed by MASQ though users who need advanced features such as
        TCP/IP source address-based or TOS-enabled routing will need to
        enable this option.

    * IP: equal cost multipath (CONFIG_IP_ROUTE_MULTIPATH) [N/y/?]
      - NO: Not needed for normal MASQ functionality

    * IP: use TOS value as routing key (CONFIG_IP_ROUTE_TOS) [N/y/?]
      - NO:  Not needed for normal MASQ functionality

    * IP: verbose route monitoring (CONFIG_IP_ROUTE_VERBOSE) [Y/n/?]
      - YES: This is useful if you use the routing code to drop IP spoofed packets (highly recommended) and you want to log them.

    * IP: large routing tables (CONFIG_IP_ROUTE_LARGE_TABLES) [N/y/?]
      - NO:  Not needed for normal MASQ functionality

    * IP: kernel level autoconfiguration (CONFIG_IP_PNP) [N/y/?] ?
      - NO:  Not needed for normal MASQ functionality

    * IP: firewalling (CONFIG_IP_FIREWALL) [Y/n/?]
      - YES: Enable the firewalling feature

    * IP: firewall packet netlink device (CONFIG_IP_FIREWALL_NETLINK) [Y/n/?]
      - OPTIONAL: Though this is OPTIONAL, this feature will allow IPCHAINS to copy some packets to UserSpace tools for additional checks

    * IP: transparent proxy support (CONFIG_IP_TRANSPARENT_PROXY) [N/y/?]
      - NO:  Not needed for normal MASQ functionality

    * IP: masquerading (CONFIG_IP_MASQUERADE) [Y/n/?]
      - YES: Enable IP Masquerade to re-address specific internal to external TCP/IP packets

    * IP: ICMP masquerading (CONFIG_IP_MASQUERADE_ICMP) [Y/n/?]
      - YES: Enable support for masquerading ICMP ping packets (ICMP error codes will be MASQed regardless).  This is an important feature for troubleshooting connections.

    * IP: masquerading special modules support (CONFIG_IP_MASQUERADE_MOD) [Y/n/?]
      - YES: Though OPTIONAL, this enables the OPTION to later enable the TCP/IP Port forwarding system to allow external computers to directly connect to specified internal MASQed machines.

    * IP: ipautofw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPAUTOFW) [N/y/m/?]
      - NO:  IPautofw is a legacy method of port forwarding.  It is mainly old code and has been found to have some issues.  NOT recommended.

    * IP: ipportfw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPPORTFW) [Y/m/n/?]
      - YES: Enables IPPORTFW which allows external computers on the Internet to directly communicate to specified internal MASQed machines.  This feature is typically used to access internal SMTP, TELNET, and WWW servers.  FTP port forwarding will need an additional patch as described in the FAQ section of the MASQ HOWTO.  Additional information on port forwarding is available in the Forwards section of this HOWTO.

    * IP: ip fwmark masq-forwarding support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_MFW) [Y/m/n/?]
      - OPTIONAL:  This is a new method of doing PORTFW.  With this option, IPCHAINS can mark packets that should have additional work on.  Using a UserSpace tool, much like IPMASQADM or IPPORFW, IPCHAINS would then automaticaly re-address the packets. Currently, this code is less tested than PORTFW but it looks promising.  For now, the recommended method is to use IPMASQADM and IPPORTFW.  If you have thoughts on MFW, please email me.

    * IP: optimize as router not host (CONFIG_IP_ROUTER) [Y/n/?]
      - YES:  This optimizes the kernel for the network subsystem though it isn't known if it makes a siginificant performance difference.

    * IP: tunneling (CONFIG_NET_IPIP) [N/y/m/?]
      - NO: This OPTIONAL section is for IPIP tunnels through IP Masq.  If you
        need tunneling/VPN functionality, it is recommended to use either GRE or
        IPSEC tunnels.

    * IP: GRE tunnels over IP (CONFIG_NET_IPGRE) [N/y/m/?]
      - NO:   This OPTIONAL selection is to enable PPTP and GRE tunnels through the IP MASQ box

      -- Non-MASQ options skipped --

    * IP: TCP syncookie support (not enabled per default) (CONFIG_SYN_COOKIES) [Y/n/?]
      - YES: HIGHLY recommended for basic TCP/IP network security

      -- Non-MASQ options skipped --

    * IP: Allow large windows (not recommended if <16Mb of memory) * (CONFIG_SKB_LARGE) [Y/n/?]
      - YES:  This is recommended to optimize Linux's TCP window

      -- Non-MASQ options skipped --

    * Network device support (CONFIG_NETDEVICES) [Y/n/?]
      - YES: Enables the Linux Network device sublayer

      -- Non-MASQ options skipped --

    * Dummy net driver support (CONFIG_DUMMY) [M/n/y/?]
      - YES:  Though OPTIONAL, this option can help when debugging problems

    == Don't forget to compile in support for your network card !! ==

      -- Non-MASQ options skipped --
    == Don't forget to compile in support for PPP/SLIP if you use a modem or
       use a PPPoE DSL modem ==

      -- Non-MASQ options skipped --

    * /proc filesystem support (CONFIG_PROC_FS) [Y/n/?]
      - YES:  Required to enable the Linux network forwarding system



  NOTE: These are just the components you need for IP Masquerade.  You
  will need to select whatever other options needed for your specific
  setup.


  ˇ  After compiling the kernel, you should compile and install the IP
     MASQ modules by doing:


         make modules; make modules_install



  ˇ  Then you should add a few lines into your /etc/rc.d/rc.local file
     to load the IP Masquerade modules and enable IP MASQ automatically
     after each reboot:



               .
               .
               .
               #rc.firewall script - Start IPMASQ and the firewall
               /etc/rc.d/rc.firewall
               .
               .
               .



  3.1.2.  Linux 2.0.x Kernels


  Please see the ``'' section for any required software, patches, etc.


  ˇ  First of all, you need the kernel source (preferably the latest
     kernel version 2.0.38 or above)


  ˇ  If this is your first time compiling the kernel, don't be scared.
     In fact, it's rather easy and it's covered in several URLs found in
     the ``'' section.



  ˇ  Unpack the kernel source to /usr/src/ with a command: tar xvzf
     linux-2.0.x.tar.gz -C /usr/src, where the "x" in 2.0.x is the
     current Linux 2.0 kernel.  Once finished, make sure there is a
     directory or symbolic link to /usr/src/linux/


  ˇ  Apply any appropriate or optional patches to the kernel source
     code.  As of 2.0.36, IP Masq does not require any specific patching
     to get everything working.  Features like IPPORTFW, PPTP, and
     Xwindows forwarders are optional.  Please refer to the ``'' section
     for URLs and the IP Masquerade Resources <http://ipmasq.cjb.net/>
     for up-to-date information and additional patch URLs.


  ˇ  Here are the MINIMUM options that are needed to be compiled into
     the kernel.  You will also need to confi gure the kernel to use
     your installed network interfaces as well. Refer to the Linux
     Kernel HOWTO <http://metalab.unc.edu/mdw/HOWTO/Kernel-HOWTO.html>
     and the README file in the kernel source directory for further
     instructions on compiling a kernel


     Please note the YES or NO ANSWERS to the following options.  Not
     all options will be available without the proper kernel patches
     described later in this HOWTO:



    * Prompt for development and/or incomplete code/drivers (CONFIG_EXPERIMENTAL) [Y/n/?]
      - YES: this will allow you to later select the IP Masquerade feature code

    * Enable loadable module support (CONFIG_MODULES) [Y/n/?]
      - YES: allows you to load kernel IP MASQ modules

    * Networking support (CONFIG_NET) [Y/n/?]
      - YES: Enables the network subsystem

    * Network firewalls (CONFIG_FIREWALL) [Y/n/?]
      - YES: Enables the IPFWADM firewall tool

    * TCP/IP networking (CONFIG_INET)
      - YES: Enables the TCP/IP protocol

    * IP: forwarding/gatewaying (CONFIG_IP_FORWARD)
      - YES: Enables Linux network packet forwarding and routing - Controlled by IPFWADM

    * IP: syn cookies (CONFIG_SYN_COOKIES) [Y/n/?]
      - YES: HIGHLY recommended for basic network security

    * IP: firewalling (CONFIG_IP_FIREWALL) [Y/n/?]
      - YES: Enable the firewalling feature

    * IP: firewall packet logging (CONFIG_IP_FIREWALL_VERBOSE) [Y/n/?]
      - YES: (OPTIONAL but HIGHLY recommended):  Allows for the reporting of firewall hits

    * IP: masquerading (CONFIG_IP_MASQUERADE [Y/n/?]
      - YES: Enable IP MASQ to re-address specific internal to external TCP/IP packets

    * IP: ipautofw masquerade support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPAUTOFW) [Y/n/?]
      - NO:  IPautofw is a legacy method of TCP/IP port forwarding.  Though it works, IPPORTFW
             is a better way so IPAUTOFW is not recommended.

    * IP: ipportfw masq support (EXPERIMENTAL) (CONFIG_IP_MASQUERADE_IPPORTFW) [Y/n/?]
      - YES: This option is ONLY AVAILABLE VIA A PATCH for the 2.0.x kernels.

             With this option, external computers on the Internet can directly communicate to specified internal MASQed machines.  This feature is typically used to access internal SMTP, TELNET, and WWW servers.  FTP port forwarding will need an additional patch as described in the FAQ section.  Additional information on port forwarding is available in the Forwards section of this HOWTO.

    * IP: ICMP masquerading (CONFIG_IP_MASQUERADE_ICMP) [Y/n/?]
      - YES: Enable support for masquerading ICMP packets. Though thought of as optional, many programs will NOT function properly with out ICMP support.

    * IP: loose UDP port managing (EXPERIMENTAL) (CONFIG_IP_MASQ_LOOSE_UDP) [Y/n/?]
      - YES: This option is ONLY AVAILABLE VIA A PATCH for the 2.0.x kernels.

             With this option, internally masqueraded computers can play NAT-friendly games over the Internet.  Explicit details are given in the FAQ section of this HOWTO.

    * IP: always defragment (CONFIG_IP_ALWAYS_DEFRAG) [Y/n/?]
      - YES:  This feature optimizes IP MASQ connections - HIGHLY recommended

    * IP: optimize as router not host (CONFIG_IP_ROUTER) [Y/n/?]
      - YES:  This optimizes the kernel for the network subsystem

    * IP: Drop source routed frames (CONFIG_IP_NOSR) [Y/n/?]
      - YES: HIGHLY recommended for basic network security

    * Dummy net driver support (CONFIG_DUMMY) [M/n/y/?]
      - YES:  Though OPTIONAL, this option can help when debugging problems

    * /proc filesystem support (CONFIG_PROC_FS) [Y/n/?]
      - YES:  Required to enable the Linux network forwarding system



  NOTE: These are just the components you need for IP Masquerade
  functionality. You will need to also select whatever other options you
  need for your specific network and hardware setup.


  ˇ  After compiling the kernel, you need to also compile and install
     the IP MASQ kernel modules by doing:


       make modules; make modules_install



  ˇ  Next, add a few lines into your /etc/rc.d/rc.local file to load the
     IP Masquerade script and thus enable IP MASQ automatically after
     each reboot:



               .
               .
               .
               #rc.firewall script - Start IPMASQ and the firewall
               /etc/rc.d/rc.firewall
               .
               .
               .



  3.1.3.  Linux 2.3.x / 2.4.x Kernels


  The 2.3.x and 2.4.x kernels are NOT covered in this HOWTO yet.  Please
  see the ``'' section for URLs, etc until it is covered by this or a
  NEW howto.



  3.2.  Assigning Private Network IP Addresses to the Internal LAN


  Since all INTERNAL MASQed machines should NOT have official Internet
  assigned addressees, there must be specific and accepted way to
  allocate address to those machines without conflicting with anyone
  else's Internet addresses.

  From the original IP Masquerade FAQ:

  RFC 1918 is the official document on which IP addresses are to be used
  on a non-connected or "private" network.  There are 3 blocks of
  numbers set aside specifically for this purpose



  Section 3: Private Address Space

  The Internet Assigned Numbers Authority (IANA) has reserved the
  following three blocks of the IP address space for private networks:

                10.0.0.0        -   10.255.255.255
                172.16.0.0      -   172.31.255.255
                192.168.0.0     -   192.168.255.255

  We will refer to the first block as "24-bit block", the second as
  "20-bit block", and to the third as "16-bit" block".  Note that the
  first block is nothing but a single class A network number, while the
  second block is a set of 16 contiguous class B network numbers, and
  third block is a set of 255 contiguous class C network numbers.



  For the record, my preference is to use the 192.168.0.0 network with a
  255.255.255.0 Class-C subnet mask and this HOWTO reflects this.  But,
  any of the above private networks are valid but just be SURE to use
  the correct subnet-mask.

  So, if you're using a Class-C network, you should number your TCP/IP
  enabled machines as 192.168.0.1, 192.168.0.2, 192.168.0.3, ...,
  192.168.0.x

  192.168.0.1 is usually the internal gateway or Linux MASQ machine to
  get out to the external network.  Please note that 192.168.0.0 and
  192.168.0.255 are the Network and Broadcast address respectively
  (these addresses are RESERVED). Avoid using these addresses on your
  machines or your network will not work properly.



  3.3.  Configuring IP Forwarding Policies

  At this point, you should have your kernel and other required packages
  installed.  All network IP addresses, gateway, and DNS addresses
  should be configured on your Linux MASQ server as well.  If you don't
  know how to configure your Linux network cards, please consult the
  HOWTOs listed in either the ``'' or ``'' sections.

  Now, the only thing left to do is to configure the IP firewalling
  tools to both FORWARD and MASQUERADE the appropriate packets to the
  appropriate machine:



       ** This can be accomplished in many different ways.  The
       following suggestions and examples worked for me, but you
       may have different ideas or needs.



       ** This section ONLY provides you with the bare minimum
       firewall ruleset to get the IP Masquerade feature working.
       Once IP MASQ has been successfully tested (as described
       later in this HOWTO), please refer to the ``'' and ``'' sec­
       tions for more secure firewall rulesets.  In addition, check
       out the IPFWADM (2.0.x) and/or IPCHAINS(2.2.x) man pages for
       more details.


  3.3.1.  Linux 2.0.x Kernels


  Create the file /etc/rc.d/rc.firewall with the following initial
  SIMPLE ruleset:



  # rc.firewall - Initial SIMPLE IP Masquerade setup for 2.0.x kernels using IPFWADM
  #
  # Load all required IP MASQ modules
  #
  #   NOTE:  Only load the IP MASQ modules you need.  All current available IP MASQ modules
  #          are shown below but are commented out from loading.

  # Needed to initially load modules
  #
  /sbin/depmod -a

  # Supports the proper masquerading of FTP file transfers using the PORT method
  #
  /sbin/modprobe ip_masq_ftp

  # Supports the masquerading of RealAudio over UDP.  Without this module,
  #       RealAudio WILL function but in TCP mode.  This can cause a reduction
  #       in sound quality
  #
  #/sbin/modprobe ip_masq_raudio

  # Supports the masquerading of IRC DCC file transfers
  #
  #/sbin/modprobe ip_masq_irc

  # Supports the masquerading of Quake and QuakeWorld by default.  This modules is
  #   for for multiple users behind the Linux MASQ server.  If you are going to play
  #   Quake I, II, and III, use the second example.
  #
  #   NOTE:  If you get ERRORs loading the QUAKE module, you are running an old
  #   -----  kernel that has bugs in it.  Please upgrade to the newest kernel.
  #
  #Quake I / QuakeWorld (ports 26000 and 27000)
  #/sbin/modprobe ip_masq_quake
  #
  #Quake I/II/III / QuakeWorld (ports 26000, 27000, 27910, 27960)
  #/sbin/modprobe ip_masq_quake 26000,27000,27910,27960

  # Supports the masquerading of the CuSeeme video conferencing software
  #
  #/sbin/modprobe ip_masq_cuseeme

  #Supports the masquerading of the VDO-live video conferencing software
  #
  #/sbin/modprobe ip_masq_vdolive


  #CRITICAL:  Enable IP forwarding since it is disabled by default
  #
  #           Redhat Users:  you may try changing the options in /etc/sysconfig/network from:
  #
  #                       FORWARD_IPV4=false
  #                             to
  #                       FORWARD_IPV4=true
  #
  echo "1" > /proc/sys/net/ipv4/ip_forward

  #CRITICAL:  Enable automatic IP defragmenting since it is disabled by default
  #
  #           This used to be a compile-time option but the behavior was changed in 2.2.12
  #
  echo "1" > /proc/sys/net/ipv4/ip_ip_always_defrag

  # Dynamic IP users:
  #
  #   If you get your Internet IP address dynamically from SLIP, PPP, or DHCP, enable this following
  #       option.  This enables dynamic-ip address hacking in IP MASQ, making the life
  #       with DialD, PPPd, and similar programs much easier.
  #
  #echo "1" > /proc/sys/net/ipv4/ip_dynaddr


  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  160 sec timeout for UDP traffic (Important for MASQ'ed ICQ users)
  #
  /sbin/ipfwadm -M -s 7200 10 160


  # DHCP:  For people who receive their external IP address from either DHCP or BOOTP
  #        such as ADSL or Cablemodem users, it is necessary to use the following
  #        before the deny command.  The "bootp_client_net_if_name" should be replaced
  #        the name of the link that the DHCP/BOOTP server will put an address on to.
  #        This will be something like "eth0", "eth1", etc.
  #
  #        This example is currently commented out.
  #
  #
  #/sbin/ipfwadm -I -a accept -S 0/0 67 -D 0/0 68 -W bootp_clients_net_if_name -P udp


  # Enable simple IP forwarding and Masquerading
  #
  #  NOTE:  The following is an example for an internal LAN address in the 192.168.0.x
  #         network with a 255.255.255.0 or a "24" bit subnet mask.
  #
  #         Please change this network number and subnet mask to match your internal LAN setup
  #
  /sbin/ipfwadm -F -p deny
  /sbin/ipfwadm -F -a m -S 192.168.0.0/24 -D 0.0.0.0/0



  Once you are finished with editing the /etc/rc.d/rc.firewall ruleset,
  make it executable by typing in "chmod 700 /etc/rc.d/rc.firewall"

  Now that the firewall ruleset is ready to go, you need to let it run
  after every reboot.  You could either do this by running it by hand
  everytime (a pain) or add it to the boot scripts.  We have covered two
  methods below:


  ˇ  Redhat and Redhat-derived distros:


  ˇ  There are two ways to load things in Redhat:  /etc/rc.d/rc.local or
     a init script in /etc/rc.d/init.d/.  The first method is the
     easiest.  All you have to do is add the line:


  ˇ  echo "Loading the rc.firewall ruleset.."

     /etc/rc.d/rc.firewall

     to the end of the /etc/rc.d/rc.local file and thats it.  The
     problem with this approach is that if you are running a STRONG
     firewall ruleset, the firewall isn't executed until the last stages
     of booting.  The preferred approach is to have the firewall loaded
     just after the networking subsystem is loaded.  For now, the HOWTO
     only covers how to do the /etc/rc.d/rc.local way.  If you want the
     stronger system, I recommend you check out Section 10 of TrinityOS
     found in the links section at the bottom of this HOWTO.


  ˇ  Slackware:


  ˇ  There are two ways to load things in Slackware: /etc/rc.d/rc.local
     or editing the /etc/rc.d/rc.inet2 file.  The first method is the
     easiest.  All you have to do is add the line:


  ˇ  echo "Loading the rc.firewall ruleset.."

     /etc/rc.d/rc.firewall

     to the end of the /etc/rc.d/rc.local file and thats it. The problem
     with this approach is that if you are running a STRONG firewall
     ruleset, the firewall isn' t executed until the last stages of
     booting.  The preferred approach is to have the firewall loaded
     just after the networking subsystem is loaded.  For now, the HOWTO
     only covers how to do the /etc/rc.d/rc.local way.  If you want the
     strong er system, I recommend you check out Section 10 of TrinityOS
     found in the links section at the bottom of this HOWTO.


  Notes on how users might want to change the above firewall ruleset:


  You could have also enabled IP Masquerading on a PER MACHINE basis
  instead of the above method enabling an ENTIRE TCP/IP network.  For
  example, say if I wanted only the 192.168.0.2 and 192.168.0.8 hosts to
  have access to the Internet and NOT any of the other internal
  machines.  I would change the in the "Enable simple IP forwarding and
  Masquerading" section (shown above) of the /etc/rc.d/rc.firewall
  ruleset.



       # Enable simple IP forwarding and Masquerading
       #
       #  NOTE:  The following is an example to only allow IP Masquerading for the 192.168.0.2
       #         and 192.168.0.8 machines with a 255.255.255.0 or a "24" bit subnet mask.
       #
       #         Please use the following in ADDITION to the simple ruleset above for specific
       #         MASQ networks.  Also change the network numbers and subnet masks to match your
       #         internal LAN setup
       #
       /sbin/ipfwadm -F -p deny
       /sbin/ipfwadm -F -a m -S 192.168.0.2/32 -D 0.0.0.0/0
       /sbin/ipfwadm -F -a m -S 192.168.0.8/32 -D 0.0.0.0/0



  Common mistakes:

  What appears to be a common mistake with new IP Masq users is to make
  the first command:

  ipfwadm -F -p masquerade



  Do NOT make your default policy be MASQUERADING.  Otherwise someone
  who can manipulate their routing tables will be able to tunnel
  straight back through your gateway, using it to masquerade their OWN
  identity!



  Again, you can add these lines to the /etc/rc.d/rc.firewall file, one
  of the other rc files you prefer, or do it manually every time you
  need IP Masquerade.

  Please see the ``'' and ``'' sections for a detailed guide on IPFWADM
  and a stronger IPFWADM ruleset example.



  3.3.2.  Linux 2.2.x Kernels


  Please note that IPFWADM is no longer the firewall tool  for
  manipulating IP Masquerading rules for both the 2.1.x and 2.2.x
  kernels.  These new kernels now use the IPCHAINS tool.  For a more
  detailed reason for this change, please see the ``'' section.


  Create the file /etc/rc.d/rc.firewall with the following initial
  SIMPLE ruleset:



  #!/bin/sh
  #
  # rc.firewall - Initial SIMPLE IP Masquerade test for 2.1.x and 2.2.x kernels using IPCHAINS
  #
  # Load all required IP MASQ modules
  #
  #   NOTE:  Only load the IP MASQ modules you need.  All current IP MASQ modules
  #          are shown below but are commented out from loading.

  # Needed to initially load modules
  #
  /sbin/depmod -a

  # Supports the proper masquerading of FTP file transfers using the PORT method
  #
  /sbin/modprobe ip_masq_ftp

  # Supports the masquerading of RealAudio over UDP.  Without this module,
  #       RealAudio WILL function but in TCP mode.  This can cause a reduction
  #       in sound quality
  #
  #/sbin/modprobe ip_masq_raudio

  # Supports the masquerading of IRC DCC file transfers
  #
  #/sbin/modprobe ip_masq_irc


  # Supports the masquerading of Quake and QuakeWorld by default.  This modules is
  #   for for multiple users behind the Linux MASQ server.  If you are going to play
  #   Quake I, II, and III, use the second example.
  #
  #   NOTE:  If you get ERRORs loading the QUAKE module, you are running an old
  #   -----  kernel that has bugs in it.  Please upgrade to the newest kernel.
  #
  #Quake I / QuakeWorld (ports 26000 and 27000)
  #/sbin/modprobe ip_masq_quake
  #
  #Quake I/II/III / QuakeWorld (ports 26000, 27000, 27910, 27960)
  #/sbin/modprobe ip_masq_quake 26000,27000,27910,27960


  # Supports the masquerading of the CuSeeme video conferencing software
  #
  #/sbin/modprobe ip_masq_cuseeme

  #Supports the masquerading of the VDO-live video conferencing software
  #
  #/sbin/modprobe ip_masq_vdolive


  #CRITICAL:  Enable IP forwarding since it is disabled by default since
  #
  #           Redhat Users:  you may try changing the options in /etc/sysconfig/network from:
  #
  #                       FORWARD_IPV4=false
  #                             to
  #                       FORWARD_IPV4=true
  #
  echo "1" > /proc/sys/net/ipv4/ip_forward


  #CRITICAL:  Enable automatic IP defragmenting since it is disabled by default in 2.2.x kernels
  #
  #           This used to be a compile-time option but the behavior was changed in 2.2.12
  #
  echo "1" > /proc/sys/net/ipv4/ip_ip_always_defrag


  # Dynamic IP users:
  #
  #   If you get your IP address dynamically from SLIP, PPP, or DHCP, enable this following
  #       option.  This enables dynamic-ip address hacking in IP MASQ, making the life
  #       with Diald and similar programs much easier.
  #
  #echo "1" > /proc/sys/net/ipv4/ip_dynaddr


  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  160 sec timeout for UDP traffic (Important for MASQ'ed ICQ users)
  #
  /sbin/ipchains -M -S 7200 10 160


  # DHCP:  For people who receive their external IP address from either DHCP or BOOTP
  #        such as ADSL or Cablemodem users, it is necessary to use the following
  #        before the deny command.  The "bootp_client_net_if_name" should be replaced
  #        the name of the link that the DHCP/BOOTP server will put an address on to?
  #        This will be something like "eth0", "eth1", etc.
  #
  #        This example is currently commented out.
  #
  #
  #/sbin/ipchains -A input -j ACCEPT -i bootp_clients_net_if_name -s 0/0 67 -d 0/0 68 -p udp

  # Enable simple IP forwarding and Masquerading
  #
  #  NOTE:  The following is an example for an internal LAN address in the 192.168.0.x
  #         network with a 255.255.255.0 or a "24" bit subnet mask.
  #
  #         Please change this network number and subnet mask to match your internal LAN setup
  #
  /sbin/ipchains -P forward DENY
  /sbin/ipchains -A forward -s 192.168.0.0/24 -j MASQ



  Once you are finished with editing the /etc/rc.d/rc.firewall ruleset,
  make it executable by typing in chmod 700 /etc/rc.d/rc.firewall


  Now that the firewall ruleset is ready to go, you need to let it run
  after every reboot.  You could either do this by running it by hand
  everytime (a pain) or add it to the boot scripts.  We have covered two
  methods below:


  ˇ  Redhat and Redhat-derived distros:


  ˇ  There are two ways to load things in Redhat:  /etc/rc.d/rc.local or
     a init script in /etc/rc.d/init.d/.  The first method is the
     easiest.  All you have to do is add the line:


  ˇ  echo "Loading the rc.firewall ruleset.." /etc/rc.d/rc.firewall

     to the end of the /etc/rc.d/rc.local file and thats it.  The
     problem with this approach is that if you are running a STRONG
     firewall ruleset, the firewall isn't executed until the last stages
     of booting.  The preferred approach is to have the firewall loaded
     just after the networking subsystem is loaded.  For now, the HOWTO
     only covers how to do the /etc/rc.d/rc.local way.  If you want the
     stronger system, I recommend you check out Section 10 of TrinityOS
     found in the links section at the bottom of this HOWTO.


  ˇ  Slackware:


  ˇ  There are two ways to load things in Slackware: /etc/rc.d/rc.local
     or editing the /etc/rc.d/rc.inet2 file.  The first method is the
     easiest.  All you have to do is add the line:


  ˇ  echo "Loading the rc.firewall ruleset.."

     /etc/rc.d/rc.firewall

     to the end of the /etc/rc.d/rc.local file and thats it. The problem
     with this approach is that if you are running a STRONG firewall
     ruleset, the firewall isn' t executed until the last stages of
     booting.  The preferred approach is to have the firewall loaded
     just after the networking subsystem is loaded.  For now, the HOWTO
     only covers how to do the /etc/rc.d/rc.local way.  If you want the
     strong er system, I recommend you check out Section 10 of TrinityOS
     found in the links section at the bottom of this HOWTO.


  Notes on how users might want to change the above firewall ruleset:

  You could have also enabled IP Masquerading on a PER MACHINE basis
  instead of the above method enabling an ENTIRE TCP/IP network. For
  example, say if I wanted only the 192.168.0.2 and 192.168.0.8 hosts to
  have access to the Internet and NOT any of the other internal
  machines. I would change the in the "Enable simple IP forwarding and
  Masquerading" section (shown above) of the /etc/rc.d/rc.firewall
  ruleset.



       #!/bin/sh
       #
       # Enable simple IP forwarding and Masquerading
       #
       #  NOTE:  The following is an example to only allow IP Masquerading for the 192.168.0.2
       #         and 192.168.0.8 machines with a 255.255.255.0 or a "24" bit subnet mask.
       #
       #         Please change this network number and subnet mask to match your internal LAN setup
       #
       /sbin/ipchains -P forward DENY
       /sbin/ipchains -A forward -s 192.168.0.2/32 -j MASQ
       /sbin/ipchains -A forward -s 192.168.0.8/32 -j MASQ



  Common mistakes:

  What appears to be a common mistake with new IP Masq users is to make
  the first command:
  /sbin/ipchains -P forward masquerade

  Do NOT make your default policy be MASQUERADING.  Otherwise someone
  who can manipulate their routing tables will be able to tunnel
  straight back through your gateway, using it to masquerade their OWN
  identity!



  Again, you can add these lines to the /etc/rc.d/rc.firewall file, one
  of the other rc files you prefer, or do it manually every time you
  need IP Masquerade.

  Please see the ``'' and ``'' sections for a detailed guide on IPCHAINS
  and a strong IPCHAINS ruleset example.  For additional details on
  IPCHAINS usage, please refer to the Linux IP CHAINS HOWTO



  4.  Configuring the other internal to-be MASQed machines

  Besides setting the appropriate IP address for each internal MASQed
  machine, you should also set each internal machine with the
  appropriate gateway IP address of the Linux MASQ server and required
  DNS servers. In general, this is rather straight forward. You simply
  enter the address of your Linux host (usually 192.168.0.1) as the
  machine's gateway address.

  For the Domain Name Service, you can add in any DNS servers that are
  available. The most apparent one should be the one that your Linux
  server is using. You can optionally add any "domain search" suffix as
  well.

  After you have properly reconfigured the internal MASQed machines,
  remember to restart their appropriate network services or reboot them.

  The following configuration instructions assume that you are using a
  Class C network with 192.168.0.1 as your Linux MASQ server's address.
  Please note that 192.168.0.0 and 192.168.0.255 are reserved TCP/IP
  address.


  As it stands, the following Platforms have been tested as internal
  MASQed machines.  This is only an EXAMPLE of all of the compatible
  OSes out there:


  ˇ  Apple Macintosh OS (with MacTCP or Open Transport)

  ˇ  Commodore Amiga (with AmiTCP or AS225-stack)

  ˇ  Digital VAX Stations 3520 and 3100 with UCX (TCP/IP stack for VMS)

  ˇ  Digital Alpha/AXP with Linux/Redhat

  ˇ  IBM AIX running on a RS/6000

  ˇ  IBM OS/2 (including Warp v3)

  ˇ  IBM OS400 running on a AS/400

  ˇ  Linux 1.2.x, 1.3.x, 2.0.x, 2.1.x, 2.2.x


  ˇ  Microsoft DOS (with NCSA Telnet package, DOS Trumpet works
     partially)

  ˇ  Microsoft Windows 3.1 (with the Netmanage Chameleon package)

  ˇ  Microsoft Windows For Workgroup 3.11 (with TCP/IP package)

  ˇ  Microsoft Windows 95, OSR2, 98, 98se

  ˇ  Microsoft Windows NT 3.51, 4.0, 2000 (both workstation and server)

  ˇ  Novell Netware 4.01 Server with the TCP/IP service

  ˇ  SCO Openserver (v3.2.4.2 and 5)

  ˇ  Sun Solaris 2.51, 2.6, 7


  4.1.  Configuring Microsoft Windows 95


  1. If you haven't installed your network card and adapter driver, do
     so now.  Description of this is beyond the scope of this document.


  2. Go to the 'Control Panel' --> 'Network'.


  3. Click on Add --> Protocol --> Manufacture: Microsoft --> Protocol:
     'TCP/IP protocol' if you don't already have it.


  4. Highlight the TCP/IP item bound to your Windows95 network card and
     select 'Properties'.  Now goto the 'IP Address' tab and set IP
     Address to 192.168.0.x, (1 < x < 255), and then set the Subnet Mask
     to 255.255.255.0


  5. Now select the "Gateway" tab and add 192.168.0.1 as your gateway
     under 'Gateway' and hit "Add".


  6. Under the 'DNS Configuration' tab, make sure to put in a name for
     this machine and enter in your official domain name.  If you don't
     have your own domain, put in the domain of your ISP.  Now, add all
     of the DNS server that your Linux host uses (usually found in
     /etc/resolv.conf).  Usually these DNS servers are located at your
     ISP though you can be running either your own CACHING or
     Authoritative DNS server on your Linux MASQ server as well.
     Optionally, you can add any appropriate domain search suffixes as
     well.


  7. Leave all the other settings as they are unless you know what
     you're doing.


  8. Click 'OK' on all dialog boxes and restart system.


  9. Ping the linux box to test the network connection: 'Start/Run',
     type: ping 192.168.0.1
     (This is only an INTERNAL LAN connection test, you can't ping the
     outside world yet.)  If you don't see "replies" to your PINGs,
     please verify your network configuration.

  10.
     You can optionally create a HOSTS file in the C:\Windows directory
     so that you can ping the "hostname" of the machines on your LAN
     without the need for a DNS server.  There is an example called
     HOSTS.SAM in the C:\windows directory.


  4.2.  Configuring Windows NT


  1. If you haven't installed your network card and adapter driver, do
     so now.  Description of this is beyond the scope of this document.


  2. Go to 'Control Panel' --> 'Network' --> Protocols


  3. Add the TCP/IP Protocol and related Components from the 'Add
     Software' menu if you don't have TCP/IP service installed already.


  4. Under 'Network Software and Adapter Cards' section, highlight the
     'TCP/IP Protocol' in the 'Installed Network Software' selection
     box.


  5. In 'TCP/IP Configuration', select the appropriate adapter, e.g.
     [1]Novell NE2000 Adapter.  Then set the IP Address to 192.168.0.x
     (1 < x < 255), then set Subnet Mask to 255.255.255.0 and Default
     Gateway to 192.168.0.1


  6. Do not enable any of the following options (unless you know what
     you are e xactly doing):


  ˇ  running on your network.

  ˇ  Put anything in the 'WINS Server' input areas :  Unless you hav e
     setup one or more WINS servers.

  ˇ  Enable IP Forwardings : Unless you are routing on your NT machine
     and really -REALLY- know EXACTLY what you're doing.


  7. Click 'DNS', fill in the appropriate information that your Linux
     host uses (usually found in /etc/resolv.conf) and then click 'OK'
     when you're done.


  8. Click 'Advanced', be sure to DISABLE 'DNS for Windows Name
     Resolution' and 'Enable LMHOSTS lookup' unless you known what these
     options do.  If you want to use a LMHOSTS file, it is stored in
     C:\winnt\system32\drivers\etc.


  9. Click 'OK' on all dialog boxes and restart system.


  10.
     Ping the linux box to test the network connection: 'File/Run',
     type: ping 192.168.0.1
     (This is only an INTERNAL LAN connection test, you can't ping the
     outside world yet.) If you don't see "replies" to your PINGs,
     please verify your network configuration.

  4.3.  Configuring Windows for Workgroup 3.11


  1. If you haven't installed your network card and adapter driver, do
     so now.  Description of this is beyond the scope of this document.


  2. Install the TCP/IP 32b package if you don't have it already.


  3. In 'Main'/'Windows Setup'/'Network Setup', click on 'Drivers'.


  4. Highlight 'Microsoft TCP/IP-32 3.11b' in the 'Network Drivers'
     section, click 'Setup'.


  5. Set the IP Address to 192.168.0.x (1 < x < 255), then set the
     Subnet Mask to 255.255.255.0 and Default Gateway to 192.168.0.1


  6. Do not enable any of the following options (unless you know what
     you are exactly doing):


  ˇ

  ˇ  Put anything in the 'WINS Server' input areas :  Unless you have
     setup one or more WINS servers.


  7. Click 'DNS', fill in the appropriate information your Linux host
     uses (usually found in /etc/resolv.conf).  Then click 'OK' when
     you're done with it.


  8. Click 'Advanced', check 'Enable DNS for Windows Name Resolution'
     and 'Enable LMHOSTS lookup' found in c:\windows.


  9. Click 'OK' on all dialog boxes and restart system.


  10.
     Ping the linux box to test the network connection: 'File/Run',
     type: ping 192.168.0.1


  4.4.  Configuring UNIX Based Systems


  1. If you haven't installed your network card and recompile your
     kernel with the appropriate adapter driver, do so now.  Description
     of this is beyond the scope of this document.

  2. Install TCP/IP networking, such as the net-tools package, if you
     don't have it already.


  3. Set IPADDR to 192.168.0.x (1 < x < 255), then set NETMASK to
     255.255.255.0, GATEWAY to 192.168.0.1, and BROADCAST to
     192.168.0.255

     For example with Redhat Linux systems, you can edit the
     /etc/sysconfig/network-scripts/ifcfg-eth0 file, or simply do it
     through the Control Panel.  These changes are different for other
     UNIXes such as SunOS, BSDi, Slackware Linux, Solaris, SuSe, Debian,
     etc...).  Please refer to your UNIX documentation for more
     information.


  4. Add your domain name service (DNS) and domain search suffix in
     /etc/resolv.conf and for the appropreiate UNIX versions, edit the
     /etc/nsswitch.conf file to enable DNS services.


  5. You may want to update your /etc/networks file depending on your
     settings.


  6. Restart the appropriate services, or simply restart your system.


  7. Issue a ping command: ping 192.168.0.1  to test the connection to
     your gateway machine.
     (This is only an INTERNAL LAN connection test, you can't ping the
     outside world yet.)  If you don't see "replies" to your PINGs,
     please verify your network configuration.


  4.5.  Configuring DOS using NCSA Telnet package


  1. If you haven't installed your network card, do so now.  Description
     of this is beyond the scope of this document.


  2. Load the appropriate packet driver. For example: using a NE2000
     Ethernet card set for I/O port 300 and IRQ 10, issue nwpd 0x60 10
     0x300


  3. Make a new directory, and then unpack the NCSA Telnet package:
     pkunzip tel2308b.zip


  4. Use a text editor to open the config.tel file


  5. Set myip=192.168.0.x (1 < x < 255), and netmask=255.255.255.0


  6. In this example, you should set hardware=packet, interrupt=10,
     ioaddr=60


  7. You should have at least one individual machine specification set
     as the gateway, i.e. the Linux host:



       name=default
       host=yourlinuxhostname
       hostip=192.168.0.1
       gateway=1



  8. Have another specification for a domain name service:

       name=dns.domain.com ; hostip=123.123.123.123; nameserver=1



  Note: substitute the appropriate information about the DNS that your
  Linux host uses


  9. Save your config.tel file


  10.
     Telnet to the linux box to test the network connection: telnet
     192.168.0.1  If you don't receive a LOGIN prompt, please verify
     your network configuration.


  4.6.  Configuring MacOS Based System Running MacTCP


  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, do so now.  Description of this is beyond the
     scope of this document.


  2. Open the MacTCP control panel.  Select the appropriate network
     driver (Ethernet, NOT EtherTalk) and click on the 'More...' button.


  3. Under 'Obtain Address:', click 'Manually'.


  4. Under 'IP Address:', select class C from the popup menu. Ignore the
     rest of this section of the dialog box.


  5. Fill in the appropriate information under 'Domain Name Server
     Information:'.


  6. Under 'Gateway Address:', enter 192.168.0.1


  7. Click 'OK' to save the settings.  In the main window of the MacTCP
     control panel, enter the IP address of your Mac (192.168.0.x, 1 < x
     < 255) in the 'IP Address:' box.


  8. Close the MacTCP control panel.  If a dialog box pops up notifying
     you to do so, restart the system.


  9. You may optionally ping the Linux box to test the network
     connection.  If you have the freeware program MacTCP Watcher, click
     on the 'Ping' button, and enter the address of your Linux box
     (192.168.0.1) in the dialog box that pops up.  (This is only an
     INTERNAL LAN connection test, you can't ping the outside world
     yet.)  If you don't see "replies" to your PINGs, please verify your
     network configuration.


  10.
     You can optionally create a Hosts file in your System Folder so
     that you can use the hostnames of the machines on your LAN.  The
     file should already exist in your System Folder, and should contain
     some (commented-out) sample entries which you can modify according
     to your needs.



  4.7.  Configuring MacOS Based System Running Open Transport


  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, do so now.  Description of this is beyond the
     scope of this document.


  2. Open the TCP/IP Control Panel and choose 'User Mode ...' from the
     Edit menu. Make sure the user mode is set to at least 'Advanced'
     and click the 'OK' button.


  3. Choose 'Configurations...' from the File menu.  Select your
     'Default' configuration and click the 'Duplicate...' button.  Enter
     'IP Masq' (or something to let you know that this is a special
     configuration) in the 'Duplicate Configuration' dialog, it will
     probably say something like 'Default copy'.  Then click the 'OK'
     button, and the 'Make Active' button


  4. Select 'Ethernet' from the 'Connect via:' pop-up.


  5. Select the appropriate item from the 'Configure:' pop-up.  If you
     don't know which option to choose, you probably should re-select
     your 'Default' configuration and quit.  I use 'Manually'.


  6. Enter the IP address of your Mac (192.168.0.x, 1 < x < 255) in the
     'IP Address:' box.


  7. Enter 255.255.255.0 in the 'Subnet mask:' box.


  8. Enter 192.168.0.1 in the 'Router address:' box.


  9. Enter the IP addresses of your domain name servers in the 'Name
     server addr.:' box.


  10.
     Enter the name of your Internet domain (e.g. 'microsoft.com') in
     the 'Starting domain name' box under 'Implicit Search Path:'.


  11.
     The following procedures are optional.  Incorrect values may cause
     erratic behavior.  If you're not sure, it's probably better to
     leave them blank, unchecked and/or un-selected.  Remove any
     information from those fields, if necessary.  As far as I know
     there is no way through the TCP/IP dialogs, to tell the system not
     to use a previously select alternate "Hosts" file.  If you know, I
     would be interested.

     Check the '802.3' if your network requires 802.3 frame types.



  12.
     Click the 'Options...' button to make sure that the TCP/IP is
     active.  I use the 'Load only when needed' option.  If you run and
     quit TCP/IP applications many times without rebooting your machine,
     you may find that unchecking the 'Load only when needed' option
     will prevent/reduce the effects on your machines memory management.
     With the item unchecked the TCP/IP protocol stacks are always
     loaded and available for use.  If checked, the TCP/IP stacks are
     automatically loaded when needed and un-loaded when not.  It's the
     loading and unloading process that can cause your machines memory
     to become fragmented.


  13.
     You may ping the Linux box to test the network connection.  If you
     have the freeware program MacTCP Watcher, click on the 'Ping'
     button, and enter the address of your Linux box (192.168.0.1) in
     the dialog box that pops up.  (This is only an INTERNAL LAN
     connection test, you can't ping the outside world yet.)   If you
     don't see "replies" to your PINGs, please verify your network
     configuration.


  14.
     You can optionally create a Hosts file in your System Folder so
     that you can use the hostnames of the machines on your LAN.  The
     file may or may not already exist in your System Folder.  If so, it
     should contain some (commented-out) sample entries which you can
     modify according to your needs.  If not, you can get a copy of the
     file from a system running MacTCP, or just create your own (it
     follows a subset of the Unix /etc/hosts file format, described on
     RFC952).  Once you've created the file, open the TCP/IP control
     panel, click on the 'Select Hosts File...' button, and open the
     Hosts file.


  15.
     Click the close box or choose 'Close' or 'Quit' from the File menu,
     and then click the 'Save' button to save the changes you have made.


  16.
     The changes take effect immediately, but rebooting the system won't
     hurt.


  4.8.  Configuring Novell network using DNS


  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, do so now.  Description of this is beyond the
     scope of this document.


  2. Downloaded tcpip16.exe from The Novell LanWorkPlace page
     <ftp.novell.com/pub/updates/unixconn/lwp5>


  3.

     edit c:\nwclient\startnet.bat



     SET NWLANGUAGE=ENGLISH
     LH LSL.COM
     LH KTC2000.COM
     LH IPXODI.COM
     LH tcpip
     LH VLM.EXE
     F:



  4.

     edit c:\nwclient\net.cfg


     Link Driver KTC2000
             Protocol IPX 0 ETHERNET_802.3
             Frame ETHERNET_802.3
             Frame Ethernet_II
             FRAME Ethernet_802.2

     NetWare DOS Requester
                FIRST NETWORK DRIVE = F
                USE DEFAULTS = OFF
                VLM = CONN.VLM
                VLM = IPXNCP.VLM
                VLM = TRAN.VLM
                VLM = SECURITY.VLM
                VLM = NDS.VLM
                VLM = BIND.VLM
                VLM = NWP.VLM
                VLM = FIO.VLM
                VLM = GENERAL.VLM
                VLM = REDIR.VLM
                VLM = PRINT.VLM
                VLM = NETX.VLM

     Link Support
             Buffers 8 1500
             MemPool 4096

     Protocol TCPIP
             PATH SCRIPT     C:\NET\SCRIPT
             PATH PROFILE    C:\NET\PROFILE
             PATH LWP_CFG    C:\NET\HSTACC
             PATH TCP_CFG    C:\NET\TCP
             ip_address      192.168.0.xxx
             ip_router       192.168.0.1



  Change the IP address in the above "ip_address" field (192.168.0.x, 1 < x < 255)
  and finally create c:\bin\resolv.cfg:

  SEARCH DNS HOSTS SEQUENTIAL
  NAMESERVER xxx.xxx.xxx.xxx
  NAMESERVER yyy.yyy.yyy.yyy



  5. Now edit the above "NAMESERVER" entries and replace them with the
     correct IP addresses for your local DNS server.


  6. Issue a ping command: ping 192.168.0.1  to test the connection to
     your gateway machine.
     (This is only an INTERNAL LAN connection test, you can't ping the
     outside world yet.)  If you don't see "replies" to your PINGs,
     please verify your network configuration.



  4.9.  Configuring OS/2 Warp


  1. If you haven't installed the appropriate driver software for your
     Ethernet adapter, do so now.  Description of this is beyond the
     scope of this document.


  2. Install the TCP/IP protocol if you don't have it already.


  3. Go to Programs/TCP/IP (LAN) / TCP/IP Settings


  4. In 'Network' add your TCP/IP Address (192.168.0.x) and set your
     netmask (255.255.255.0)


  5. Under 'Routing' press 'Add'. Set the Type to 'default' and type the
     IP Address of your Linux Box in the Field 'Router Address'.
     (192.168.0.1).


  6. Set the same DNS (Nameserver) Address that your Linux host uses in
     'Hosts'.


  7. Close the TCP/IP control panel. Say yes to the following
     question(s).



  8. Reboot your system


  9. You may ping the Linux box to test the network configuration. Type
     'ping 192.168.0.1' in a 'OS/2 Command prompt Window'. When ping
     packets are received all is ok.


  4.10.  Configuring OS/400 on a IBM AS/400

  The description of how to configure TCP/IP on OS/400 version V4R1M0
  running on a AS/400 is beyond the scope of this document.

  1) To perform any communications configuration tasks on your AS/400,
  you must have the special authority of *IOSYSCFG (I/O System
  Configuration) defined in your user profile. You can check the
  characteristics of your user profile with the DSPUSRPRF command.

  2) Type GO CFGTCP command th reach the Configure TCP/IP menu.

  3) Select Option 2 - Work with TCP/IP Routes.

  4) Enter a 1 on the Opt field to add a route.  * In Route Destination
  type *DFTROUTE * In Subnet Mask type *NONE * In Type of Service type
  *NORMAL * In Nex Hop type the address of your gataway (the Linux box)

  4.11.  Configuring Other Systems

  The same logic should apply to setting up other platforms.  Consult
  the sections above.  If you're interested in writing about any of
  systems that have not been covered yet, please send a detail setup
  instruction to ambrose@writeme.com and dranch@trinnet.net.


  5.  Testing IP Masquerade



  Finally, it's time to give IP Masquerading an official try after all
  this hard work.  If you haven't already rebooted your Linux box, do so
  to make sure the machines boots ok, executes the /etc/rc.d/rc.firewall
  ruleset, etc. Next, make sure that both the internal LAN connection
  and connection of your Linux hosts to the Internet is okay.

  Now do the following:


  ˇ  One:  From an internal MASQed computer, try pinging your local IP
     address (i.e. ping 192.168.0.10 ).  This will verify that TCP/IP is
     correctly working on the local machine.  If this doesn't work, make
     sure that TCP/IP is correctly configured on the MASQed PC as
     described earlier in this HOWTO.


  ˇ  Two:  On the MASQ server itself, ping then internal IP address of
     the MASQ network (i.e. ping 192.168.0.1).  Now Then ping the
     external IP address connected to the Internet.  This address might
     be your PPP, Ethernet, etc. address connected to your ISP.  If you
     don't know what this IP address is, run the Linux command
     "/sbin/ifconfig" on the MASQ server to get the Internet address.
     This will confirm that the MASQ server has full network
     connectivity.


  ˇ  Three:  Back on a internal MASQed computer, try pinging the IP
     address of the Masquerading Linux box's internal Ethernet card,
     (i.e. ping 192.168.0.1).  This will prove that your internal
     network and routing is ok.  If this fails, make sure Ethernet cards
     of the MASQ server and the MASQed computer have "link".  This is
     usually a LED light on either the back of each Ethernet card and
     also on the Ethernet hub/switch (if you are using one).


  ˇ  Four:  From an internal MASQed computer, ping the IP address of the
     MASQ server's external TCP/IP address obtained in item TWO above.
     This address might be your PPP, Ethernet, etc. address connected to
     your ISP.  This ping test will prove that masquerading is working
     (ICMP Masquerading specifically).  If it doesn't work, make sure
     that you enabled "ICMP Masquerading" in the kernel and "IP
     Forwarding" in your /etc/rc.d/rc.firewall script.  Also make sure
     that the /etc/rc.d/rc.firewall ruleset loaded ok.  Try run the
     /etc/rc.d/rc.firewall script manually for now to see if it runs ok.

  If you still can't get things to work, take a look at the output from

  ˇ  "ifconfig" : Make sure your Internet connection is UP and you have
     the correct IP address for the Internet connection


  ˇ  "netstat -rn" : Make sure your default gateway (the column one with
     the IP address in the Gateway column) is set

  ˇ  "cat /proc/sys/net/ipv4/ip_forward" : Make sure it says "1" so that
     Linux forwarding is enabled


  ˇ  "/sbin/ipfwadm -F -l" for 2.0.x or "/sbin/ipchains -F -L" for 2.2.x
     users : Make sure you have MASQ enabled


  ˇ  Five:  From an internal MASQed computer, now ping a static TCP/IP
     address out on the Internet (i.e. ping 152.19.254.81 (this is
     http://metalab.unc.edu - home of the LDP).  If this works, that
     means that ICMP Masquerading is working over the Internet.  If it
     didn't work, again check your Internet connection.  If this still
     doesn't work, make sure you are using the simple rc.firewall
     ruleset and that you have ICMP Masqurading compiled into the Linux
     kernel.  Also, make sure that the ruleset that enable IP MASQ is
     pointing to the correct EXNTERNAL interface.


  ˇ  Six:  Now try TELNETing to a remote IP address (i.e. telnet
     152.2.254.81 (metalab.unc.edu - Note that this might take a while
     to get a login prompt since this is a VERY busy server.)  Did you
     get a login prompt after a while?  If that worked, that means that
     TCP Masquerading is running ok.  If not, try TELNETing to some
     other hosts you think will support TELNET like 198.182.196.55
     (www.linux.org).  If this still doesn't work, make sure you are
     using the simple rc.firewall ruleset for now.


  ˇ  Seven:  Now try TELNETing to a remote HOSTNAME (i.e. "telnet
     metalab.unc.edu" (152.2.254.81).  If this works, this means that
     DNS is working fine as well.  If this didn't work but step FOUR did
     work, make sure that you have valid DNS servers configured on your
     MASQed computer.


  ˇ  Eight:  As a last test, try browsing some 'INTERNET' WWW sites on
     one of your MASQed machines, and see if you can reach them.  For
     example, access the Linux Documentation Project site.  If this
     works, you can be fairly certain that everything is working FINE!

  If you see The Linux Documentation Project homepage, then
  CONGRATULATIONS! It's working!  If that WWW site comes up correctly,
  then all other standard network tolls such as PING, TELNET, SSH, and
  with their related IP MASQ modules loaded: FTP, Real Audio, IRC DCCs,
  Quake I/II/III, CuSeeme, VDOLive, etc. should work fine!  If FTP, IRC,
  RealAudio, Quake I/II/III, etc. aren't working or are performing
  poorly, make sure their associated Masquerading modules are loaded by
  running "lsmod" and also be sure you are loading the module with any
  non-default server ports.  If you don't see your needed module, make
  sure your /etc/rc.d/rc.firewall script is loading them (i.e. remove
  the # character for a give IP MASQ module).



  6.  Other IP Masquerade Issues and Software Support



  6.1.  Problems with IP Masquerade

  Some TCP/IP application protocols will not currently work with Linux
  IP Masquerading because they either assume things about port numbers
  or encode TCP/IP addresses and/or port numbers in their data stream.
  These latter protocols need specific proxies or IP MASQ modules built
  into the masquerading code to make them work.
  6.2.  Incoming services

  By default, Linux IP Masquerading cannot handle incoming services at
  all but there are a few ways of allowing them.

  If you do not require high levels of security then you can simply
  forward or redirect IP ports.  There are various ways of doing this
  though the most stable method is to use IPPORTFW.  For more
  information, please see the ``'' section.

  If you wish to have some level of authorization on incoming
  connections then you will need to either configure TCP-wrappers or
  Xinetd to then allow only specific IP addresses through.  The TIS
  Firewall Toolkit is a good place to look for tools and information.

  More details on incoming security can be found in the TrinityOS
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> document
  and at IP Masquerade Resource <http://ipmasq.cjb.net>.



  6.3.  Supported Client Software and Other Setup Notes



       ** The Linux Masquerade Application list <http://www.tsmser­
       vices.com/masq> has a lot of good information regarding
       applications that work through Linux IP masquerading.  This
       site was recently taken over by Steve Grevemeyer who impli­
       mented it with a full database backend.  Its a great
       resource!


  Generally, any application that uses standard TCP and UDP should work.
  If you have any suggestion, hints, etc., please see the IP Masquerade
  Resource <http://ipmasq.cjb.net/> for more details.


  6.3.1.  Network Clients that -Work- with IP Masquerade

  General Clients:


     Archie
        all supported platforms, file searching client (not all archie
        clients are supported)


     FTP
        all supported platforms, with the ip_masq_ftp.o kernel module
        for active FTP connections.


     Gopher client
        all supported platforms


     HTTP
        all supported platforms, WWW surfing


     IRC
        all IRC clients on various supported platforms, DCC is supported
        via the ip_masq_irc.o module


     NNTP (USENET)
        all supported platforms, USENET news client


     PING
        all platforms, with ICMP Masquerading kernel option


     POP3
        all supported platforms, email clients


     SSH
        all supported platforms, Secure TELNET/FTP clients


     SMTP
        all supported platforms, email servers like Sendmail, Qmail,
        PostFix, etc.


     TELNET
        all supported platforms, remote session


     TRACEROUTE
        UNIX and Windows based platforms , some variations may not work


     VRML
        Windows(possibly all supported platforms), virtual reality
        surfing


     WAIS client
        all supported platforms


  Multimedia and Communication Clients:


     Alpha Worlds
        Windows, Client-Server 3D chat program


     CU-SeeMe
        all supported platforms, with the ip_masq_cuseeme module loaded,
        please see the ``'' section for more details.


     ICQ
        all supported clients.  Requires the Linux kernel to be compiled
        with IPPORTFW support and ICQ is configured to be behind a NON-
        SOCKS proxy.  A full description of this configuration is in the
        ``'' section.


     Internet Phone 3.2
        Windows, Peer-to-peer audio communications, people can reach you
        only if you initiate the call, but people cannot call you
        without a specific port forwarding setup.  See the ``'' section
        for more details.

     Internet Wave Player
        Windows, network streaming audio


     Powwow
        Windows, Peer-to-peer Text audio whiteboard communications,
        people can reach you only if you initiate the call, but people
        cannot call you without a specific port forwarding setup.  See
        the ``'' se ction for more details.


     Real Audio Player
        Windows, network streaming audio, higher quality available with
        the ip_masq_raudio UDP module


     True Speech Player 1.1b
        Windows, network streaming audio


     VDOLive
        Windows, with the ip_masq_vdolive patch


     Worlds Chat 0.9a
        Windows, Client-Server 3D chat program



  Games - See the ``'' section for more details on the LooseUDP patch


     Battle.net
        Works but requires TCP ports 116 and 118 and UDP port 6112
        IPPORTFWed to the game machine.  See the ``'' section for more
        details.  Please note that FSGS and Bnetd servers still require
        IPPORTFW since they haven't been re-written to be NAT-friendly.


     BattleZone 1.4
        Works with LooseUDP patch and new NAT-friendly .DLLs from
        Activision


     Dark Reign 1.4
        Works with LooseUDP patch or requires TCP ports 116 and 118 and
        UDP port 6112 IPPORTFWed to the game machine.  See the ``''
        section for more details.


     Diablo
        Works with LooseUDP patch or requires TCP ports 116 and 118 and
        UDP port 6112 IPPORTFWed to the game machine.  Newer versions of
        Diablo use only TCP port 6112 and UDP port 6112.  See the ``''
        section for more details.


     Heavy Gear 2
        Works with LooseUDP patch or requires TCP ports 116 and 118 and
        UDP port 6112 IPPORTFWed to the game machine.  See the ``''
        section for more details.


     Quake I/II/III
        Works right out of the box but requires the ip_masq_quake module
        if there are more than one Quake I/II/III player behind a MASQ
        box.  Also, this module only supports Quake I and QuakeWorld by
        default.  If you need to support Quake II or non-default server
        ports, please see the module install section of the ``'' and
        ``'' rulesets.


     StarCraft
        Works with the LooseUDP patch and IPPORTFWing TCP and UDP ports
        6112 to the internal MASQed game machine.  See the ``'' section
        for more details.


     WorldCraft
        Works with LooseUDP patch


  Other Clients:


     Linux net-acct package
        Linux, network administration-account package


     NCSA Telnet 2.3.08
        DOS, a suite containing telnet, ftp, ping, etc.


     PC-anywhere for Windows
        MS-Windows, Remotely controls a PC over TCP/IP, only work if it
        is a client but not a host without a specific port forwarding
        setup.  See the ``'' section for more details.


     Socket Watch
        uses NTP - network time protocol


  6.3.2.  Clients that do not have full support in IP MASQ:



     All H.323 programs
        - MS Netmeeting, Intel Internet Phone Beta 2 - Connects but
        voice travels one way (out).  Check out Equivalence's PhonePatch
        <http://www.equival.com.au/phonepatch/index.html> H.323 gateway
        for one possible solution.

        UPDATE:  There is now ALPHA module available on the MASQ WWW
        site or at ftp://ftp.coritel.it/pub/linux/ip_masq/
        <ftp://ftp.coritel.it/pub/linux/ip_masq/> to work with Microsoft
        Netmeeting v3.x code on 2.2.x kernels.  There is also another
        module version on the MASQ WWW site specifically for Netmeeting
        2.x with 2.0.x kerneks.


     Intel Streaming Media Viewer Beta 1
        Cannot connect to server


     Netscape CoolTalk
        Cannot connect to opposite side


     WebPhone
        Cannot work at present (it makes invalid assumptions about
        addresses).
  6.4.  Stronger IP Firewall (IPFWADM) Rulesets



  This section provides a more in-depth guide on using the 2.0.x
  firewall tool, IPFWADM.  See below for IPCHAINS rulesets

  This example is for a firewall/masquerade system behind a PPP link
  with a static PPP address (dynamic PPP instructions are included but
  disabled).  The trusted interface is 192.168.0.1 and the PPP interface
  IP address has been changed to protect the guilty :).  I have listed
  each incoming and outgoing interface individually to catch IP spoofing
  as well as stuffed routing and/or masquerading. Anything not
  explicitly allowed is FORBIDDEN (well.. rejected actually).  If your
  IP MASQ box breaks after implementing this rc.firewall script, be sure
  that you edited it for your configuration and check your
  /var/log/messages or /var/adm/messages SYSLOG file for any firewall
  errors.

  For more comprehensive examples of a strong IP Masqueraded IPFWADM
  rulesets for PPP, Cablemodem users, etc., please see TrinityOS -
  Section 10 <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>
  and GreatCircle's Firewall WWW page

  NOTE: If you get a dynamically assigned TCP/IP address from your ISP
  (PPP, ADSL, Cablemodems, etc.), you CANNOT load this strong ruleset
  upon boot.  You will either need to reload this firewall ruleset EVERY
  TIME you get a new IP address or make your /etc/rc.d/rc.firewall
  ruleset more intelligent.  To do this for PPP users, carefully read
  and un-comment out the properly lines in the "Dynamic PPP IP fetch"
  section below.   You can also find more details in the TrinityOS -
  Section 10 <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>
  doc for more details on Strong rulesets and Dynamic IP addresses.

  Please also be aware that there are several GUI Firewall creation
  tools available as well.  Please see the ``'' section for full
  details.

  Lastly, if you are using a STATIC PPP IP address, change the
  "ppp_ip="your.static.PPP.address"" line to reflect your address.

  ----------------------------------------------------------------



  #!/bin/sh
  #
  # /etc/rc.d/rc.firewall: An example of a semi-STRONG IPFWADM firewall ruleset
  #

  PATH=/sbin:/bin:/usr/sbin:/usr/bin

  # testing, wait a bit then clear all firewall rules.
  # uncomment following lines if you want the firewall to automatically
  # disable after 10 minutes.
  # (sleep 600; \
  # ipfwadm -I -f; \
  # ipfwadm -I -p accept; \
  # ipfwadm -O -f; \
  # ipfwadm -O -p accept; \
  # ipfwadm -F -f; \
  # ipfwadm -F -p accept; \
  # ) &

  # Load all required IP MASQ modules
  #
  #   NOTE:  Only load the IP MASQ modules you need.  All current IP MASQ modules
  #          are shown below but are commented from loading.

  # Needed to initially load modules
  #
  /sbin/depmod -a

  # Supports the proper masquerading of FTP file transfers using the PORT method
  #
  /sbin/modprobe ip_masq_ftp

  # Supports the masquerading of RealAudio over UDP.  Without this module,
  #       RealAudio WILL function but in TCP mode.  This can cause a reduction
  #       in sound quality
  #
  #/sbin/modprobe ip_masq_raudio

  # Supports the masquerading of IRC DCC file transfers
  #
  #/sbin/modprobe ip_masq_irc


  # Supports the masquerading of Quake and QuakeWorld by default.  This modules is
  #   for for multiple users behind the Linux MASQ server.  If you are going to play
  #   Quake I, II, and III, use the second example.
  #
  #   NOTE:  If you get ERRORs loading the QUAKE module, you are running an old
  #   -----  kernel that has bugs in it.  Please upgrade to the newest kernel.
  #
  #Quake I / QuakeWorld (ports 26000 and 27000)
  #/sbin/modprobe ip_masq_quake
  #
  #Quake I/II/III / QuakeWorld (ports 26000, 27000, 27910, 27960)
  #/sbin/modprobe ip_masq_quake 26000,27000,27910,27960


  # Supports the masquerading of the CuSeeme video conferencing software
  #
  #/sbin/modprobe ip_masq_cuseeme

  #Supports the masquerading of the VDO-live video conferencing software
  #
  #/sbin/modprobe ip_masq_vdolive


  #CRITICAL:  Enable IP forwarding since it is disabled by default since
  #
  #           Redhat Users:  you may try changing the options in /etc/sysconfig/network from:
  #
  #                       FORWARD_IPV4=false
  #                             to
  #                       FORWARD_IPV4=true
  #
  echo "1" > /proc/sys/net/ipv4/ip_forward


  #CRITICAL:  Enable automatic IP defragmenting since it is disabled by default in 2.2.x kernels
  #
  #           This used to be a compile-time option but the behavior was changed in 2.2.12
  #
  echo "1" > /proc/sys/net/ipv4/ip_ip_always_defrag


  # Dynamic IP users:
  #
  #   If you get your IP address dynamically from SLIP, PPP, or DHCP, enable this following
  #       option.  This enables dynamic-ip address hacking in IP MASQ, making the life
  #       with Diald and similar programs much easier.
  #
  #echo "1" > /proc/sys/net/ipv4/ip_dynaddr


  # Specify your Static IP address here.
  #
  #   If you have a DYNAMIC IP address, you need to make this ruleset understand your
  #   IP address everytime you get a new IP.  To do this, enable the following one-line
  #   script.  (Please note that the different single and double quote characters MATTER).
  #
  #
  #   DHCP users:
  #   -----------
  #   If you get your TCP/IP address via DHCP, **you will need ** to enable the #ed out command
  #   below underneath the PPP section AND replace the word "ppp0" with the name of your EXTERNAL
  #   Internet connection (eth0, eth1, etc).  It should be also noted that the DHCP server can
  #   change IP addresses on you.  To fix this, users should configure their DHCP client to
  #   re-run the firewall ruleset everytime the DHCP lease is renewed.
  #
  #     NOTE #1:  Some newer DHCP clients like "pump" do NOT have this ability to run scripts
  #               after a lease-renew.  Because of this, you need to replace it with something
  #               like "dhcpcd" or "dhclient".
  #
  #     NOTE #2:  The syntax for "dhcpcd" has changed in recent versions.
  #
  #               Older versions used syntax like:
  #                         dhcpcd -c /etc/rc.d/rc.firewall eth0
  #
  #               Newer versions use syntax like:
  #                         dhcpcd eth0 /etc/rc.d/rc.firewall
  #
  #
  #   PPP users:
  #   ----------
  #   If you aren't already aware, the /etc/ppp/ip-up script is always run when a PPP
  #   connection comes up.  Because of this, we can make the ruleset go and get the
  #   new PPP IP address and update the strong firewall ruleset.
  #
  #   If the /etc/ppp/ip-up file already exists, you should edit it and add a line
  #   containing "/etc/rc.d/rc.firewall" near the end of the file.
  #
  #   If you don't already have a /etc/ppp/ip-up sccript, you need to create the following
  #   link to run the /etc/rc.d/rc.firewall script.
  #
  #       ln -s /etc/rc.d/rc.firewall /etc/ppp/ip-up
  #
  #   * You then want to enable the #ed out shell command below *
  #
  #
  # PPP and DHCP Users:
  # -------------------
  # Remove the # on the line below and place a # in front of the line after that.
  #
  #ppp_ip="`/sbin/ifconfig ppp0 | grep 'inet addr' | awk '{print $2}' | sed -e 's/.*://'`"
  #
  ppp_ip="your.static.PPP.address"


  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  60 sec timeout for UDP traffic (MASQ'ed ICQ users must enable a 30sec firewall timeout in ICQ itself)
  #
  /sbin/ipfwadm -M -s 7200 10 60


  #############################################################################
  # Incoming, flush and set default policy of reject. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  /sbin/ipfwadm -I -f
  /sbin/ipfwadm -I -p reject

  # local interface, local machines, going anywhere is valid
  #
  /sbin/ipfwadm -I -a accept -V 192.168.0.1 -S 192.168.0.0/24 -D 0.0.0.0/0

  # remote interface, claiming to be local machines, IP spoofing, get lost
  #
  /sbin/ipfwadm -I -a reject -V $ppp_ip -S 192.168.0.0/24 -D 0.0.0.0/0 -o

  # remote interface, any source, going to permanent PPP address is valid
  #
  /sbin/ipfwadm -I -a accept -V $ppp_ip -S 0.0.0.0/0 -D $ppp_ip/32

  # loopback interface is valid.
  #
  /sbin/ipfwadm -I -a accept -V 127.0.0.1 -S 0.0.0.0/0 -D 0.0.0.0/0

  # catch all rule, all other incoming is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  /sbin/ipfwadm -I -a reject -S 0.0.0.0/0 -D 0.0.0.0/0 -o


  #############################################################################
  # Outgoing, flush and set default policy of reject. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  /sbin/ipfwadm -O -f
  /sbin/ipfwadm -O -p reject

  # local interface, any source going to local net is valid
  #
  /sbin/ipfwadm -O -a accept -V 192.168.0.1 -S 0.0.0.0/0 -D 192.168.0.0/24

  # outgoing to local net on remote interface, stuffed routing, deny
  #
  /sbin/ipfwadm -O -a reject -V $ppp_ip -S 0.0.0.0/0 -D 192.168.0.0/24 -o

  # outgoing from local net on remote interface, stuffed masquerading, deny
  #
  /sbin/ipfwadm -O -a reject -V $ppp_ip -S 192.168.0.0/24 -D 0.0.0.0/0 -o

  # outgoing from local net on remote interface, stuffed masquerading, deny
  #
  /sbin/ipfwadm -O -a reject -V $ppp_ip -S 0.0.0.0/0 -D 192.168.0.0/24 -o

  # anything else outgoing on remote interface is valid
  #
  /sbin/ipfwadm -O -a accept -V $ppp_ip -S $ppp_ip/32 -D 0.0.0.0/0

  # loopback interface is valid.
  #
  /sbin/ipfwadm -O -a accept -V 127.0.0.1 -S 0.0.0.0/0 -D 0.0.0.0/0

  # catch all rule, all other outgoing is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  /sbin/ipfwadm -O -a reject -S 0.0.0.0/0 -D 0.0.0.0/0 -o


  #############################################################################
  # Forwarding, flush and set default policy of deny. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  /sbin/ipfwadm -F -f
  /sbin/ipfwadm -F -p deny

  # Masquerade from local net on local interface to anywhere.
  #
  /sbin/ipfwadm -F -a masquerade -W ppp0 -S 192.168.0.0/24 -D 0.0.0.0/0
  #
  # catch all rule, all other forwarding is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  /sbin/ipfwadm -F -a reject -S 0.0.0.0/0 -D 0.0.0.0/0 -o

  #End of file.



  With IPFWADM, you can block traffic to a particular site using the -I,
  -O or -F rules.  Remember that the set of rules are scanned top to
  bottom and "-a" tells IPFWADM to "append" this new rule to the
  existing set of rules.  So with this in mind, any specific
  restrictions need to come before global rules. For example:

  Using -I (input ) rules:

  Probably the fastest and most efficient method to block traffic but it
  only stops the MASQed machines and NOT the the firewall machine
  itself. Of course you might want to allow that combination.

  Anyway, to block 204.50.10.13:


  In the /etc/rc.d/rc.firewall ruleset:



  ... start of -I rules ...

  # reject and log local interface, local machines going to 204.50.10.13
  #
  /sbin/ipfwadm -I -a reject -V 192.168.0.1 -S 192.168.0.0/24 -D 204.50.10.13/32 -o

  # local interface, local machines, going anywhere is valid
  #
  /sbin/ipfwadm -I -a accept -V 192.168.0.1 -S 192.168.0.0/24 -D 0.0.0.0/0

  ... end of -I rules ...



  Using -O (output) rules:

  This is the slower method to block traffic because the packets go
  through masquerading first before they are dropped.  Yet, this rule
  even stops the firewall machine from accessing the forbidden site.



  ... start of -O rules ...

  # reject and log outgoing to 204.50.10.13
  #
  /sbin/ipfwadm -O -a reject -V $ppp_ip -S $ppp_ip/32 -D 204.50.10.13/32 -o

  # anything else outgoing on remote interface is valid
  #
  /sbin/ipfwadm -O -a accept -V $ppp_ip -S $ppp_ip/32 -D 0.0.0.0/0

  ... end of -O rules ...



  Using -F (forward) rules:

  Probably slower than -I (input) rules for blocking traffic, this still
  only stops masqueraded machines (e.g. internal machines).   The
  firewall machine can still reach forbidden site(s).


  ... start of -F rules ...

  # Reject and log from local net on PPP interface to 204.50.10.13.
  #
  /sbin/ipfwadm -F -a reject -W ppp0 -S 192.168.0.0/24 -D 204.50.10.13/32 -o

  # Masquerade from local net on local interface to anywhere.
  #
  /sbin/ipfwadm -F -a masquerade -W ppp0 -S 192.168.0.0/24 -D 0.0.0.0/0

  ... end of -F rules ...



  There is no need for a special rule to allow machines on the
  192.168.0.0/24 network to go to 204.50.11.0. Why?  It is already
  covered by the global MASQ rule.

  NOTE:  There is more than one way of coding the interfaces in the
  above rules.  For example instead of "-V 192.168.255.1" you can code
  "-W eth0", instead of "-V $ppp_ip" , you can use "-W ppp0".  The "-V"
  method was phased out with the imgration to IPCHAINS but for IPFWADM
  users, its personal choice and documentation more than anything.



  6.5.  Stronger IP Firewall (IPCHAINS) rulesets



  This section provides a more in-depth guide on using the 2.2.x
  firewall tool, IPCHAINS.  See above for IPFWADM rulesets.

  This example is for a firewall/masquerade system behind a PPP link
  with a static PPP address (dynamic PPP instructions are included but
  disabled).  The trusted interface is 192.168.0.1 and the PPP interface
  IP address has been changed to protect the guilty :).  I have listed
  each incoming and outgoing interface individually to catch IP spoofing
  as well as stuffed routing and/or masquerading. A nything not
  explicitly allowed is FORBIDDEN (well.. rejected actually).  If your
  IP MASQ box breaks after implementing this rc.firewall script, be sure
  that you edited it for your configuration and check your
  /var/log/messages or /var/adm/messages SYSLOG file for any firewall
  errors.

  For more comprehensive examples of a strong IP Masqueraded IPFWADM
  rulesets for PPP, Cablemodem users, etc., please see TrinityOS -
  Section 10 <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>
  and GreatCircle's Firewall WWW page

  NOTE #1: Linux 2.2.x kernels less than 2.2.11 have a IPCHAINS
  fragmentation bug.   Because of this, people running strong IPCHAINS
  rulesets are open to attack.  Please upgrade your kernel to a fixed
  version.

  NOTE #2: If you get a dynamically assigned TCP/IP address from your
  ISP (PPP, ADSL, Cablemodems, etc.), you CANNOT load this strong
  ruleset upon boot.  You will either need to reload this firewall
  ruleset EVERY TIME you get a new IP address or make your
  /etc/rc.d/rc.firewall ruleset more intelligent.  To do this for PPP
  users, carefully read and un-comment out the properly lines in the
  "Dynamic PPP IP fetch" section below.   You can also find more details
  in the TrinityOS - Section 10
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> doc for
  more details on Strong rulesets and Dynamic IP addresses.

  Please also be aware that there are several GUI Firewall creation
  tools available as well.  Please see the ``'' section for full
  details.

  Lastly, if you are using a STATIC PPP IP address, change the
  "ppp_ip="your.static.PPP.address"" line to reflect your address.

  ----------------------------------------------------------------



  #!/bin/sh
  #
  # /etc/rc.d/rc.firewall: An example of a Semi-Strong IPCHAINS firewall ruleset.
  #

  PATH=/sbin:/bin:/usr/sbin:/usr/bin

  # Load all required IP MASQ modules
  #
  #   NOTE:  Only load the IP MASQ modules you need.  All current IP MASQ modules
  #          are shown below but are commented from loading.

  # Needed to initially load modules
  #
  /sbin/depmod -a

  # Supports the proper masquerading of FTP file transfers using the PORT method
  #
  /sbin/modprobe ip_masq_ftp

  # Supports the masquerading of RealAudio over UDP.  Without this module,
  #       RealAudio WILL function but in TCP mode.  This can cause a reduction
  #       in sound quality
  #
  /sbin/modprobe ip_masq_raudio

  # Supports the masquerading of IRC DCC file transfers
  #
  #/sbin/modprobe ip_masq_irc


  # Supports the masquerading of Quake and QuakeWorld by default.  This modules is
  #   for for multiple users behind the Linux MASQ server.  If you are going to play
  #   Quake I, II, and III, use the second example.
  #
  #   NOTE:  If you get ERRORs loading the QUAKE module, you are running an old
  #   -----  kernel that has bugs in it.  Please upgrade to the newest kernel.
  #
  #Quake I / QuakeWorld (ports 26000 and 27000)
  #/sbin/modprobe ip_masq_quake
  #
  #Quake I/II/III / QuakeWorld (ports 26000, 27000, 27910, 27960)
  #/sbin/modprobe ip_masq_quake 26000,27000,27910,27960


  # Supports the masquerading of the CuSeeme video conferencing software
  #
  #/sbin/modprobe ip_masq_cuseeme

  #Supports the masquerading of the VDO-live video conferencing software
  #
  #/sbin/modprobe ip_masq_vdolive


  #CRITICAL:  Enable IP forwarding since it is disabled by default since
  #
  #           Redhat Users:  you may try changing the options in /etc/sysconfig/network from:
  #
  #                       FORWARD_IPV4=false
  #                             to
  #                       FORWARD_IPV4=true
  #
  echo "1" > /proc/sys/net/ipv4/ip_forward


  #CRITICAL:  Enable automatic IP defragmenting since it is disabled by default in 2.2.x kernels
  #
  #           This used to be a compile-time option but the behavior was changed in 2.2.12
  #
  echo "1" > /proc/sys/net/ipv4/ip_ip_always_defrag


  # Dynamic IP users:
  #
  #   If you get your IP address dynamically from SLIP, PPP, or DHCP, enable this following
  #       option.  This enables dynamic-ip address hacking in IP MASQ, making the life
  #       with Diald and similar programs much easier.
  #
  #echo "1" > /proc/sys/net/ipv4/ip_dynaddr
  # Specify your Static IP address here.



  #
  #   If you have a DYNAMIC IP address, you need to make this ruleset understand your
  #   IP address everytime you get a new IP.  To do this, enable the following one-line
  #   script.  (Please note that the different single and double quote characters MATTER).
  #
  #
  #   DHCP users:
  #   -----------
  #   If you get your TCP/IP address via DHCP, **you will need ** to enable the #ed out command
  #   below underneath the PPP section AND replace the word "ppp0" with the name of your EXTERNAL
  #   Internet connection (eth0, eth1, etc) on the lines for "ppp-ip" and "extip".  It should be
  #   also noted that the DHCP server can change IP addresses on you.  To fix this, users should
  #   configure their DHCP client to re-run the firewall ruleset everytime the DHCP lease is
  #   renewed.
  #
  #     NOTE #1:  Some newer DHCP clients like "pump" do NOT have this ability to run scripts
  #               after a lease-renew.  Because of this, you need to replace it with something
  #               like "dhcpcd" or "dhclient".
  #
  #     NOTE #2:  The syntax for "dhcpcd" has changed in recent versions.
  #
  #               Older versions used syntax like:
  #                         dhcpcd -c /etc/rc.d/rc.firewall eth0
  #
  #               Newer versions use syntax like:
  #                         dhcpcd eth0 /etc/rc.d/rc.firewall
  #
  #
  #   PPP users:
  #   ----------
  #   If you aren't already aware, the /etc/ppp/ip-up script is always run when a PPP
  #   connection comes up.  Because of this, we can make the ruleset go and get the
  #   new PPP IP address and update the strong firewall ruleset.
  #
  #   If the /etc/ppp/ip-up file already exists, you should edit it and add a line
  #   containing "/etc/rc.d/rc.firewall" near the end of the file.
  #
  #   If you don't already have a /etc/ppp/ip-up sccript, you need to create the following
  #   link to run the /etc/rc.d/rc.firewall script.
  #
  #       ln -s /etc/rc.d/rc.firewall /etc/ppp/ip-up
  #
  #   * You then want to enable the #ed out shell command below *
  #
  #
  # PPP and DHCP Users:
  # -------------------
  # Remove the # on the line below and place a # in front of the line after that.
  #
  #extip= "`/sbin/ifconfig ppp0 | grep 'inet addr' | awk '{print $2}' | sed -e 's/.*://'`"

  # For PPP users with STATIC IP addresses:
  #
  extip="your.static.PPP.address"

  # ALL PPP and DHCP users must set this for the correct EXTERNAL interface name
  extint="ppp0"

  # Assign the internal IP
  intint="eth0"
  intnet="192.168.1.0/24"


  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  60 sec timeout for UDP traffic (MASQ'ed ICQ users must enable a 30sec firewall timeout in ICQ itself)
  #
  ipchains -M -S 7200 10 60

  #############################################################################
  # Incoming, flush and set default policy of reject. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  ipchains -F input
  ipchains -P input REJECT

  # local interface, local machines, going anywhere is valid
  #
  ipchains -A input -i $intint -s $intnet -d 0.0.0.0/0 -j ACCEPT

  # remote interface, claiming to be local machines, IP spoofing, get lost
  #
  ipchains -A input -i $extint -s $intnet -d 0.0.0.0/0 -l -j REJECT

  # remote interface, any source, going to permanent PPP address is valid
  #
  ipchains -A input -i $extint -s 0.0.0.0/0 -d $extip/32 -j ACCEPT

  # loopback interface is valid.
  #
  ipchains -A input -i lo -s 0.0.0.0/0 -d 0.0.0.0/0 -j ACCEPT

  # catch all rule, all other incoming is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  ipchains -A input -s 0.0.0.0/0 -d 0.0.0.0/0 -l -j REJECT

  #############################################################################
  # Outgoing, flush and set default policy of reject. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  ipchains -F output
  ipchains -P output REJECT

  # local interface, any source going to local net is valid
  #
  ipchains -A output -i $intint -s 0.0.0.0/0 -d $intnet -j ACCEPT

  # outgoing to local net on remote interface, stuffed routing, deny
  #
  ipchains -A output -i $extint -s 0.0.0.0/0 -d $intnet -l -j REJECT

  # outgoing from local net on remote interface, stuffed masquerading, deny
  #
  ipchains -A output -i $extint -s $intnet -d 0.0.0.0/0 -l -j REJECT

  # anything else outgoing on remote interface is valid
  #
  ipchains -A output -i $extint -s $extip/32 -d 0.0.0.0/0 -j ACCEPT

  # loopback interface is valid.
  #
  ipchains -A output -i lo -s 0.0.0.0/0 -d 0.0.0.0/0 -j ACCEPT

  # catch all rule, all other outgoing is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  ipchains -A output -s 0.0.0.0/0 -d 0.0.0.0/0 -l -j REJECT

  #############################################################################
  # Forwarding, flush and set default policy of deny. Actually the default policy
  # is irrelevant because there is a catch all rule with deny and log.
  #
  ipchains -F forward
  ipchains -P forward DENY

  # Masquerade from local net on local interface to anywhere.
  #
  ipchains -A forward -i $extint -s $intnet -d 0.0.0.0/0 -j MASQ
  #
  # catch all rule, all other forwarding is denied and logged. pity there is no
  # log option on the policy but this does the job instead.
  #
  ipchains -A forward -s 0.0.0.0/0 -d 0.0.0.0/0 -l -j REJECT

  #End of file.



  With IPCHAINS, you can block traffic to a particular site using the
  "input", "output", and/or "forward" rules.  Remember that the set of
  rules are scanned t op to bottom and "-A" tells IPCHIANS to "append"
  this new rule to the existing set of rules.  So with this in mind, any
  specific restrictions need to come bef ore global rules. For example:

  Using "input" rules:

  Probably the fastest and most efficient method to block traffic but it
  only stops the MASQed machines and NOT the firewall machine itself. Of
  course you might want to allow that combination.

  Anyway, to block 204.50.10.13:

  In the /etc/rc.d/rc.firewall ruleset:

  ... start of "input" rules ...

  # reject and log local interface, local machines going to 204.50.10.13
  #
  ipchains -A input -s 192.168.0.0/24 -d 204.50.10.13/32 -l -j REJECT


  # local interface, local machines, going anywhere is valid
  #
  ipchains -A input -s 192.168.0.0/24 -d 0.0.0.0/0 -l -j ACCEPT


  ... end of "input" rules ...

  Using "output" rules:

  This is the slower method to block traffic because the packets must go
  through masquerading first before they are dropped.  Yet, this rule
  even stops the firewall machine from accessing the forbidden site.


  ... start of "output" rules ...

  # reject and log outgoing to 204.50.10.13
  #
  ipchains -A output -s $ppp_ip/32 -d 204.50.10.13/32 -l -j REJECT


  # anything else outgoing on remote interface is valid
  #
  ipchains -A output -s $ppp_ip/32 -d 0.0.0.0/0 -l -j ACCEPT


  ... end of "output" rules ...



  Using "forward" rules:

  Probably slower than "input" rules for blocking traffic, this still
  only stops masqueraded machines (e.g. internal machines).  The
  firewall machine can still reach forbidden site(s).



  ... start of "forward" rules ...

  # Reject and log from local net on PPP interface to 204.50.10.13.
  #
  ipchains -A forward -i ppp0 -s 192.168.0.0/24 -d 204.50.10.13/32 -l -j REJECT


  # Masquerade from local net on local interface to anywhere.
  #
  ipchains -A forward -i ppp0 -s 192.168.0.0/24 -d 0.0.0.0/0 -j MASQ

  ... end of "forward" rules ...



  No need for a special rule to allow machines on the 192.168.0.0/24
  network to go to 204.50.11.0. Why?  It is already covered by the
  global MASQ rule.

  NOTE: Unlike IPFWADM, IPCHIANS has only one way of coding the
  interfaces name.  IPCHAINS uses the "-i eth0" option where as IPFWADM
  had both "-W" for the interface name and "-V" for the interface's IP
  address.



  6.6.  IP Masquerading multiple internal networks

  Masquerading more than one internal network is fairly simple.  You
  need to first make sure that all of your networks are running
  correctly (both internal and external).  You then need to enable
  traffic to pass to both the other internal interfaces and to be MASQed
  to the Internet.


  Next, you need to enable Masquerading on the INTERNAL interfaces.
  This example shows two internal interfaces eth1 (192.168.0.1) and eth2
  (192.168.1.1) will be MASQed out of interface eth0.  In your
  rc.firewall ruleset next to the existing MASQ enable line, add the
  following:


  ˇ  2.0.x kernels with IPFWADM

       #Enable internal interfaces to communication between each other
       /sbin/ipfwadm -F -a accept -V 192.168.0.1 -D 192.168.1.0/24
       /sbin/ipfwadm -F -a accept -V 192.168.1.1 -D 192.168.0.0/24

       #Enable internal interfaces to MASQ out to the Internet
       /sbin/ipfwadm -F -a masq -W eth0 -S 192.168.0.0/24 -D 0.0.0.0/0
       /sbin/ipfwadm -F -a masq -W eth0 -S 192.168.1.0/24 -D 0.0.0.0/0



  ˇ  2.2.x kernels with IPCHAINS

       #Enable internal interfaces to communication between each other
       /sbin/ipchains -A forward -i eth1 -d 192.168.1.0/24
       /sbin/ipchains -A forward -i eth2 -d 192.168.0.0/24

       #Enable internal interfaces to MASQ out to the Internet
       /sbin/ipchains -A forward -j MASQ -i eth0 -s 192.168.0.0/24 -d 0.0.0.0/0
       /sbin/ipchains -A forward -j MASQ -i eth0 -s 192.168.1.0/24 -d 0.0.0.0/0



  6.7.  IP Masquerade and Dial-on-Demand Connections



  1. If you would like to setup your network to automatically dial up
     the Internet, ether the Diald demand dial-up or new versions of the
     PPPd packages will be of great utility.  Diald is the recommended
     solution due to its more granular configuration.


  2. To setup Diald, please check out the Setting Up Diald for Linux
     Page <http://home.pacific.net.sg/~harish/diald.config.html> or
     TrinityOS - Section 23
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>


  3. Once Diald and IP Masq have been setup properly, any MASQed client
     machines that initiate a web, telnet or ftp session will make the
     Linux box dynamically bring up its Internet link.


  4. There is a timeout that will occur with the first connection.  This
     is inevitable if you are using analog modems.  The time taken to
     establish the modem link and the PPP connections may cause your
     client program (WWW browser, etc.).  This isn't common though.  If
     this does happen, just retry that Internet traffic request (say a
     WWW page) again and it should come up fine.  You can also try
     setting echo "1" > /proc/sys/net/ipv4/ip_dynaddr kernel option to
     help with this initial setup.


  6.8.  IPPORTFW, IPMASQADM, IPAUTOFW, REDIR, UDPRED, and other Port
  Forwarding tools


  IPPORTFW, IPAUTOFW, REDIR, UDPRED, and other programs are generic TCP
  and/or UDP port forwarding tools for Linux IP Masquerade.  These tools
  are typically used with or as a replacement for specific IP MASQ
  modules like the current ones for FTP, Quake, etc. With port
  forwarders, you can now re-direct data connections from the Internet
  to an internal, privately addressed machine behind your IP MASQ
  server.  This forwarding ability includes network protocols such as
  TELNET, WWW, SMTP, FTP (with a special patch - see below), ICQ, and
  many others.

  NOTE:  If you are just looking to do port forwarding without IP
  Masquerading, you will STILL NEED to enable IP Masquerading in both
  the kernel AND in either your IPFWADM or IPCHAINS ruleset to then be
  able to use Linux's port forwarding tools.

  So why all the different choices?  IPAUTOFW, REDIR, and UDPRED (all
  URLs are in the ``'' section) were the first tools available to IP
  MASQ users to allow this functionality.  Later, as Linux IP Masquerade
  matured, these tools were eventually replaced by IPPORTFW which is a
  more intelligent solution.  Because of the availablity of the newer
  tools, it is *HIGHLY DISCOURAGED* to use the old tools such as
  IPAUTOFW and REDIR because they don't properly notify the Linux kernel
  of their presence and can ultimately CRASH your Linux server with
  extreme use.

  Before jumping right into installing either the 2.0.x IPPORTFW or
  2.2.x version of IPMASQADM with IPPORTFW support, network security can
  be an issue with any port forwarder.  The reason for this is because
  these tools basically create a hole in the packet firewall for the
  forwarded TCP/UDP ports.  Though this doesn't pose any threat to your
  Linux machine, it might be an issue to the internal machine that this
  traffic is being forwarded to.  No worries though, this is what Steven
  Clarke (the author of IPPORTFW) had to say about that:



               "Port Forwarding is only called within masquerading functions so it
               fits inside the same IPFWADM/IPCHAINS rules. Masquerading is an extension to
               IP forwarding. Therefore, ipportfw only sees a packet if it fits
               both the input and masquerading ipfwadm rule sets."



  With this said, it's important to have a strong firewall ruleset.
  Please see the ``'' and ``'' sections for more details on strong
  rulesets.


  So, to install IPPORTFW forwarding support for either a 2.0.x or 2.2.x
  kernel, you need to re-compile the Linux kernel to support IPPORTFW.

  ˇ  2.0.x users will need to apply a simple kernel option patch (see
     below)

  ˇ  2.2.x kernel users will already have the IPPORTFW kernel option
     available via IPMASQADM



  6.8.1.  IPPORTFW on 2.0.x kernels


  First, make sure you have the newest 2.0.x kernel uncompressed into
  /usr/src/linux.  If you haven't already done this, please see the ``''
  section for full details.  Next, download the "ipportfw.c" program and
  the "subs-patch-x.gz" kernel patch from the ``'' section into the
  /usr/src/ directory.

  NOTE:  Please replace the "x" in the "subs-patch-x.gz" file name with
  the most current version available on the site.


  Now, copy the IPPORTFW patch (subs-patch-x.gz) into the Linux
  directory


               cp /usr/src/subs-patch-1.37.gz /usr/src/linux



  Next, apply the kernel patch to create the IPPORTFW kernel option:


               cd /usr/src/linux
               zcat subs-patch-1.3x.gz | patch -p1



  Next, if you plan on port forwarding FTP traffic to an internal
  server, you will have to apply a NEW IP_MASQ_FTP module patch found in
  the ``'' section.  More details regarding this are later in this
  section.


  Ok, time to compile the kernel as shown in the ``'' section.  Be sure
  to say YES to the IPPORTFW option now available when you configure the
  kernel.  Once the compile is complete and you have rebooted, return to
  this section.

  Now with a newly compiled kernel, please compile and install the
  actual "IPPORTFW" program


               cd /usr/src
               gcc ipportfw.c -o ipportfw
               mv ipportfw /usr/local/sbin



  Now, for this example, we are going to allow ALL WWW Internet traffic
  (port 80) hitting your Internet TCP/IP address to then be forwarded to
  the internal Masqueraded machine at IP address 192.168.0.10.

  NOTE:  Once you enable a port forwarder on port 80, that port can no
  longer be used by the Linux IP Masquerade server.  TO be more
  specific, if you have a WWW server already running on the MASQ server
  and then you port forward port 80 to an internal MASQed computer, ALL
  internet users will see the WWW pages pages from the -INTERNAL- WWW
  server and not the pages on your IP MASQ server.  The only work around
  for this is to port forward some other port, say 8080, to your
  internal MASQ machine.  Though this will work, all Internet users will
  have to append :8080 to the URL to then contact the internal MASQed
  WWW server.

  Anyway, to enable port forwarding, edit the /etc/rc.d/rc.firewall
  ruleset.  Add the follow lines but be sure to replace the word
  "$extip" with your Internet IP address.

  NOTE:  If you use get a DYNAMIC TCP/IP address from your ISP (PPP,
  ADSL, Cablemodems, etc.), you will NEED to make your
  /etc/rc.d/rc.firewall ruleset more intelligent.  To do this, please
  see TrinityOS - Section 10
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> for more
  details on strong rulesets and Dynamic IP addresses.



               /etc/rc.d/rc.firewall
               --

               #echo "Enabling IPPORTFW Redirection on the external LAN.."
               #
               /usr/local/sbin/ipportfw -C
               /usr/local/sbin/ipportfw -A -t$extip/80 -R 192.168.0.10/80

               --



  That's it!  Just re-run your /etc/rc.d/rc.firewall ruleset and test it
  out!

  If you get the error message "ipfwadm: setsockopt failed: Protocol not
  available", you AREN'T running your new kernel.  Make sure that you
  moved the new kernel over, re-run LILO, and then reboot again.


  Port Forwarding FTP servers:

  If you plan on port forwarding FTP to an internal machine, things get
  more complicated.  The reason for this is because the standard
  IP_MASQ_FTP kernel module wasn't written for this.  Fortunately, Fred
  Viles wrote a modified IP_MASQ_FTP module to make things work.  If you
  are curious what EXACTLY is the issues, download the following archive
  since Fred documents it quite well.  Also understand that this patch
  is somewhat experimental and should be treated as such.  It should be
  also noted that this patch is ONLY available for the 2.0.x kernels at
  this time.  Though some worked has already been done on a 2.2.x port,
  if you are interested in helping complete this port, please email Fred
  Viles - fv@episupport.com directly.

  So, to get the 2.0.x patch working, you need to:



  ˇ  Apply the IPPORTFW kernel patch as shown earlier in this section
     FIRST.


  ˇ  Download the "msqsrv-patch-36" from Fred Viles's FTP server in the
     ``'' section and put it into /usr/src/linux.


  ˇ  Patch the kernel with this new code by running "cat msqsrv-patch-36
     | patch -p1"


  ˇ  Next, replace the original "ip_masq_ftp.c" kernel module with the
     new one


  ˇ  mv /usr/src/linux/net/ipv4/ip_masq_ftp.c
     /usr/src/linux/net/ipv4/ip_masq_ftp.c.orig

  ˇ  mv /usr/src/linux/ip_masq_ftp.c
     /usr/src/linux/net/ipv4/ip_masq_ftp.c


  ˇ  Lastly build and install the kernel with this new code in place.

  Once this is complete, edit the /etc/rc.d/rc.firewall ruleset and add
  the follow lines but be sure to replace the word "$extip" with your
  Internet IP address.

  NOTE:  If you use get a DYNAMIC TCP/IP address from your ISP (PPP,
  ADSL, Cablemodems, etc.), you will NEED to make your
  /etc/rc.d/rc.firewall ruleset more intelligent.  To do this, please
  see TrinityOS - Section 10
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> for more
  details on strong rulesets and Dynamic IP addresses.

  This example, like above, will allow ALL FTP Internet traffic (port
  21) hitting your Internet TCP/IP address to then be forwarded to the
  internal Masqueraded machine at IP address 192.168.0.10.

  NOTE:  Once you enable a port forwarder on port 21, that port can no
  longer be used by the Linux IP Masquerade server.  To be more
  specific, if you have a FTP server already running on the MASQ server,
  a port forward will now give all Internet users the FTP files from the
  -INTERNAL- FTP server and not the files on your IP MASQ server.



               /etc/rc.d/rc.firewall
               --

               #echo "Enabling IPPORTFW Redirection on the external LAN.."
               #
               /usr/local/sbin/ipportfw -C
               /usr/local/sbin/ipportfw -A -t$extip/21 -R 192.168.0.10/21

               --



  That's it!  Just re-run your /etc/rc.d/rc.firewall ruleset and test it
  out!

  If you get the error message "ipchains: setsockopt failed: Protocol
  not available", you AREN'T running your new kernel.  Make sure that
  you moved the new kernel over, re-run LILO, and then reboot again.  If
  you are sure you are running your new kernel, run the command "ls
  /proc/net" and make sure the "ip_portfw" file exists.  If it doesn't,
  you must have made an error when configuring your kernel.  Try again.



  6.8.2.  IPMASQADM with IPPORTFW support on 2.2.x kernels


  First, make sure you have the newest 2.2.x kernel uncompressed into
  /usr/src/linux.  If you haven't already done this, please see the ``''
  section for full details.  Next, download the "ipmasqadm.c" program
  from the ``'' section into the /usr/src/ directory.

  Next, you'll need to compile the 2.2.x kernel as shown in the ``''
  section.   Be sure to say YES to the IPPORTFW option when you
  configure the kernel.  Once the kernel compile is complete and you
  have rebooted, return to this section.

  Now, compile and install the IPMASQADM tool:



               cd /usr/src
               tar xzvf ipmasqadm-x.tgz
               cd ipmasqadm-x
               make
               make install



  Now, for this example, we are going to allow ALL WWW Internet traffic
  (port 80) hitting your Internet TCP/IP address to then be forwarded to
  the internal Masqueraded machine at IP address 192.168.0.10.

  NOTE:  At this time, it is beleived that this modified IP_MASQ_FTP
  module for port forwarded FTP connections will NOT work for the 2.2.x
  kernels.  If you feel experimental, please try porting it to the 2.2.x
  kernels and email David your results.

  NOTE: Once you enable a port forwarder on port 80, that port can no
  longer be used by the Linux IP Masquerade server.  To be more
  specific, if you have a WWW server already running on the MASQ server,
  a port forward will now give all Internet users the WWW pages from the
  -INTERNAL- WWW server and not the pages on your IP MASQ server.

  Anyway, to enable port forwarding, edit the /etc/rc.d/rc.firewall
  ruleset.  Add the follow lines but be sure to replace the word
  "$extip" with your Internet IP address.

  NOTE:  If you use get a DYNAMIC TCP/IP address from your ISP (PPP,
  ADSL, Cablemodems, etc.), you will NEED to make your
  /etc/rc.d/rc.firewall ruleset more intelligent.  TO do this, please
  see TrinityOS - Section 10
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> for more
  details on strong rulesets and Dynamic IP addresses.  I'll give you a
  hint though:  /etc/ppp/ip-up for PPP users.



          /etc/rc.d/rc.firewall
          --

          #echo "Enabling IPPORTFW Redirection on the external LAN.."
          #
          /usr/sbin/ipmasqadm portfw -f
          /usr/sbin/ipmasqadm portfw -a -P tcp -L $extip 80 -R 192.168.0.10 80

          --



  That's it!  Just re-run your /etc/rc.d/rc.firewall ruleset and test it
  out!

  If you get the error message "ipchains: setsockopt failed: Protocol
  not available", you AREN'T running your new kernel.  Make sure that
  you moved the new kernel over, re-run LILO, and then reboot again.  If
  you are sure you are running your new kernel, run the command "ls
  /proc/net/ip_masq" and make sure the "portfw" file exists.  If it
  doesn't, you must have made an error when configuring your kernel.
  Try again.



  6.9.  CU-SeeMe and Linux IP-Masquerade


  Linux IP Masquerade supports CuSeeme via the "ip_masq_cuseeme" kernel
  module.  This kernel modules should be loaded in the
  /etc/rc.d/rc.firewall script.  Once the "ip_masq_cuseeme" module is
  installed, you should be able to both initiate and receive CuSeeme
  connections to remote reflectors and/or users.

  NOTE:  It is recommended to use the IPPORTFW tool instead of the old
  IPAUTOFW tool for running CuSeeme.

  If you need more explicit information on configuring CuSeeme, see
  Michael Owings's CuSeeMe page <http://www.swampgas.com/vc/ipmcus.htm>
  for a Mini-HOWTO or The IP Masquerade Resources for a mirror of the
  Mini-HOWTO.



  6.10.  Mirabilis ICQ

  There are two methods of getting ICQ to work behind a Linux MASQ
  server.  One solution is to use a new ICQ Masq module and the other
  solution is to use IPPORTFW.

  The ICQ module has some benefits.  It allows for simple setup of
  multiple ICQ users behind a MASQ server.  It also doesn't require any
  special changes to the ICQ client(s).  Recently, the 2.2.x version of
  the module was updated to support file transfer and read-time chat.
  Yet, for the 2.0.x kernel module, file transfers and real-time chat
  still isn't fully supported.  Anyway, I now feel this is the PREFERRED
  method to get ICQ working with IP Masq running on 2.2.x+ kernels.


  With the IPPORTFW setup, you will have to make some changes on both
  Linux and ICQ clients but all ICQ messaging, URLs, chat, file
  transfer, etc. work.

  If you are interested in Andrew Deryabin's djsf@usa.net ICQ IP Masq
  module for the 2.2.x kernels.  Please see the ``'' section for
  details.

  If you rather use the classic method of getting ICQ to run behind a
  MASQ server, follow these steps:

  ˇ  First, you need to be running a Linux kernel with IPPPORTFW
     enabled.  Please see the ``'' section for more details.


  ˇ  Next, you need to add the following lines to your
     /etc/rc.d/rc.firewall file.  This example assumes that 10.1.2.3 is
     your external Internet IP address and your internal MASQed ICQ
     machine is 192.168.0.10:

     The following example is for a 2.0.x kernel with IPFWADM:


       I have included two examples here for the user:  Either once works
       fine:

       Example #1
       --
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2000 -R 192.168.0.10/2000
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2001 -R 192.168.0.10/2001
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2002 -R 192.168.0.10/2002
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2003 -R 192.168.0.10/2003
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2004 -R 192.168.0.10/2004
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2005 -R 192.168.0.10/2005
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2006 -R 192.168.0.10/2006
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2007 -R 192.168.0.10/2007
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2008 -R 192.168.0.10/2008
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2009 -R 192.168.0.10/2009
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2010 -R 192.168.0.10/2010
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2011 -R 192.168.0.10/2011
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2012 -R 192.168.0.10/2012
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2013 -R 192.168.0.10/2013
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2014 -R 192.168.0.10/2014
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2015 -R 192.168.0.10/2015
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2016 -R 192.168.0.10/2016
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2017 -R 192.168.0.10/2017
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2018 -R 192.168.0.10/2018
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2019 -R 192.168.0.10/2019
       /usr/local/sbin/ipportfw -A -t10.1.2.3/2020 -R 192.168.0.10/2020
       --

       Example #2
       --
       port=2000
       while [ $port -le 2020 ]
         do
             /usr/local/sbin/ipportfw -A t10.1.2.3/$port -R 192.168.0.10/$port
             port=$((port+1))
         done
       --



  The following example is for a 2.2.x kernel with IPCHAINS:



    I have included two examples here for the user:  Either once works
    fine:

    Example #1
    --
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2000 -R 192.168.0.10 2000
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2001 -R 192.168.0.10 2001
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2002 -R 192.168.0.10 2002
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2003 -R 192.168.0.10 2003
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2004 -R 192.168.0.10 2004
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2005 -R 192.168.0.10 2005
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2006 -R 192.168.0.10 2006
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2007 -R 192.168.0.10 2007
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2008 -R 192.168.0.10 2008
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2009 -R 192.168.0.10 2009
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2010 -R 192.168.0.10 2010
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2011 -R 192.168.0.10 2011
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2012 -R 192.168.0.10 2012
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2013 -R 192.168.0.10 2013
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2014 -R 192.168.0.10 2014
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2015 -R 192.168.0.10 2015
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2016 -R 192.168.0.10 2016
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2017 -R 192.168.0.10 2017
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2018 -R 192.168.0.10 2018
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2019 -R 192.168.0.10 2019
    /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 2020 -R 192.168.0.10 2020
    --

    Example #2
    --
    port=2000
    while [ $port -le 2020 ]
      do
          /usr/local/sbin/ipmasqadm portfw -a -P tcp -L 10.1.2.3 $port -R 192.168.0.10 $port
          port=$((port+1))
      done
    --



  ˇ  Once your new rc.firewall is ready, reload the ruleset to make sure
     things are ok by simple typing in "/etc/rc.d/rc.firewall".  If you
     get any errors, you either don't have IPPORTFW support in the
     kernel or you made a typo in the rc.firewall file.


  ˇ  Now, in ICQ's Preferences-->Connection, configure it to be "Behind
     a LAN" and "Behind a firewall or Proxy".  Now, click on "Firewall
     Settings" and configure it to be "I don't use a SOCK5 proxy".  Also
     note that it was repviously recommended to change ICQ's "Firewall
     session timeouts" to "30" seconds BUT many users have found that
     ICQ becomes unreliable.  It has been found that ICQ is more
     reliable with its stock timeout setting (don't enable that ICQ
     option) and simply change MASQ's timeout to 160 seconds.  You can
     see how to change this timeout in the ``'' and ``'' rulesets.
     Finally, click on Next and configure ICQ to "Use the following TCP
     listen ports.." from "2000" to "2020".  Now click done.

     Now ICQ will tell you that you have to restart ICQ for the changes
     to take effect.  To be honest, I had to REBOOT the Windows9x
     machine to get things to work right but other people say otherwise.
     So.. try it both ways.


  ˇ  It should also be noted that one user told me that simply
     portforwarding port 4000 to his ICQ machine worked best. He
     reported that everything worked fine (chat, file transfers, etc)
     WITHOUT re-configuring ICQ from its default settings.  Your mileage
     might vary on this topic but I though you might like to hear about
     this alternative configuration.



  6.11.  Gamers:  The LooseUDP patch


  The LooseUDP patch allows NAT-friendly games that usually use UDP
  connections to both WORK and perform quite well behind a Linux IP
  Masquerade server.  Currently, LooseUDP is available as a patch for
  2.0.36+ kernels and it is already built into 2.2.3+ kernels.  To get
  this running, only a few things are required:


  ˇ  Have the newest 2.0.x kernel sources uncompressed in the
     /usr/src/linux directory


  ˇ  ABSOLUTELY REQUIRED for v2.0.x:  Download and install the IPPORTFW
     patch from the ``'' section and as described in the ``'' Section of
     the HOWTO.


  ˇ  Download the LooseUDP patch from the ``'' section

  Now, put the LooseUDP patch in the /usr/src/linux directory.   Once
  this is done, type in:


       For a compressed patch file:  zcat loose-udp-2.0.36.patch.gz | patch
       -p1



       For a NON-compressed patch file:  cat loose-udp-2.0.36.patch | patch
       -p1


  Now, depending on your version of "patch", You will then see the
  following text:



       patching file `CREDITS'
       patching file `Documentation/Configure.help'
       patching file `include/net/ip_masq.h'
       patching file `net/ipv4/Config.in'
       patching file `net/ipv4/ip_masq.c'



  If you see the text "Hunk FAILED" only ONCE and ONLY ONCE at the very
  beginning of the patching, don't be alarmed.  You probably have an old
  patch file (this as been fixed) but it still works.  If it fails
  completely, make sure you have applied the IPPORTFW kernel patch
  FIRST.

  Once the patch is installed, re-configure the kernel as shown in the
  ``'' section and be sure to say "Y" to the "IP: loose UDP port
  managing (EXPERIMENTAL) (CONFIG_IP_MASQ_LOOSE_UDP) [Y/n/?]" option.
  Once you are running the new LooseUDP enabled kernel, you should be
  good to go for most NAT-friendly games.  Some URLs have been given for
  patches to make games like BattleZone and others NAT friendly.  Please
  see the ``'' section for more details.



  7.  Frequently Asked Questions



  If you can think of any useful FAQ suggestions, please send it to
  ambrose@writeme.com and dranch@trinnet.net.  Please clearly state the
  question and an appropriate answer (if you have it).  Thank you!



  7.1.  What Linux Distributions support IP Masquerading out of the box?

  If your Linux distribution doesn't support IP MASQ out of the box,
  don't worry.  All you have to do is re-compile a kernel as shown above
  in this HOWTO.

  NOTE:  If you can help us fill out this table, please email
  ambrose@writeme.com or dranch@trinnet.net.


  ˇ  Caldera       < v1.2   : NO  - ?

  ˇ  Caldera         v1.3   : YES - 2.0.35 based

  ˇ  Caldera         v2.2   : YES - 2.2.5 based

  ˇ  Caldera eServer v2.3   : YES - ? based

  ˇ  Debian          v1.3   : NO  - ?

  ˇ  Debian          v2.0   : NO  - ?

  ˇ  Debian          v2.1   : YES - 2.2.1 based

  ˇ  Debian          v2.2   : YES - 2.2.15 based

  ˇ  DLX Linux       v?     :  ?  - ?

  ˇ  DOS Linux       v?     :  ?  - ?

  ˇ  FloppyFW              v1.0.2 :  ?  - ?

  ˇ  Hal91 Linux     v?     :  ?  - ?

  ˇ  Linux Mandrake  v5.3   : YES - ?

  ˇ  Linux Mandrake  v6.0   : YES - 2.2.5 based

  ˇ  Linux PPC       vR4    :  NO - ?

  ˇ  Linux Pro       v?     :  ?  - ?

  ˇ  LinuxWare       v?     :  ?  - ?

  ˇ  Mandrake        v6.0   : YES - ?

  ˇ  Mandrake        v6.1   : YES - ?

  ˇ  Mandrake        v7.0   : YES - 2.2.14

  ˇ  MkLinux         v?     :  ?  - ?

  ˇ  MuLinux         v3rl   : YES - ?

  ˇ  Redhat        < v4.x   : NO  - ?

  ˇ  Redhat          v5.0   : YES - ?

  ˇ  Redhat          v5.1   : YES - 2.0.34 based

  ˇ  Redhat          v5.2   : YES - 2.0.36 based

  ˇ  Redhat          v6.0   : YES - 2.2.5 based

  ˇ  Redhat          v6.1   : YES - 2.2.12 based

  ˇ  Slackware       v3.0   :  ?  - ?

  ˇ  Slackware       v3.1   :  ?  - ?

  ˇ  Slackware       v3.2   :  ?  - ?

  ˇ  Slackware       v3.3   :  ?  - 2.0.34 based

  ˇ  Slackware       v3.4   :  ?  - ?

  ˇ  Slackware       v3.5   :  ?  - ?

  ˇ  Slackware       v3.6   :  ?  - ?

  ˇ  Slackware       v3.9   :  ?  - 2.0.37pre10 based

  ˇ  Slackware       v4.0   :  ?  - ?

  ˇ  Slackware       v7.0   : YES - 2.2.13 based

  ˇ  Stampede Linux  v?     :  ?  - ?

  ˇ  SuSE            v5.2   : YES - ?

  ˇ  SuSE            v5.3   : YES - ?

  ˇ  SuSE            v6.0   : YES - ?

  ˇ  SuSE            v6.1   : YES - 2.2.5 based

  ˇ  SuSE            v6.3   : YES - 2.2.13 based

  ˇ  Tomsrbt Linux   v?     :  ?  - ?

  ˇ  TurboLinux Lite v4.0   : YES - ?

  ˇ  TurboLinux v6.0        : YES - 2.2.12 based

  ˇ  TriLinux        v?     :  ?  - ?

  ˇ  Yggdrasil Linux v?     :  ?  - ?



  7.2.  What are the minimum hardware requirements and any limitations
  for IP Masquerade?  How well does it perform?


  A 486/66 box with 16MB of RAM was more than sufficient to fill a
  1.54Mb/s T1 100%!  MASQ has also be known run quite well on 386SX-16s
  with 8MB or RAM.  Yet, it should be noted that Linux IP Masquerade
  starts thrashing with more than 500 MASQ entries.

  The only application that I known that can temporarily break Linux IP
  Masquerade is GameSpy.  Why?  When it refreshes its lists, it creates
  10,000s of quick connections in a VERY short time.  Until these
  sessions timeout, the MASQ tables become "FULL".  See the ``'' section
  of the FAQ for more details.


  While we are at it:

  There is a hard limit of 4096 concurrent connections each for TCP &
  UDP.  This limit can be changed by fiddling the values in
  /usr/src/linux/net/ipv4/ip_masq.h - a upwards limit of 32000 should by
  OK.  If you want to change the limit - you need to change the
  PORT_MASQ_BEGIN & PORT_MASQ_END values to get an appropriately sized
  range above 32K and below 64K.



  7.3.  I've checked all my configurations, I still can't get IP Mas­
  querade to work.  What should I do?


  ˇ  Stay calm.  Get yourself a cup of tea, coffee, soda, etc., and have
     a rest.  Once your mind is clear, try the suggestions mentioned
     below.  Setting up Linux IP Masquerading is NOT hard but there are
     several concepts that will be new to you.


  ˇ  Again, go through all the steps in the ``'' section.  99% of all
     first-time Masquerade users who have problems haven't looked here.


  ˇ  Check the IP Masquerade Mailing List Archives
     <http://www.indyramp.com/lists/masq/>, most likely your question or
     problem is a common one and can be found in a simple Archive
     search.


  ˇ  Check out the TrinityOS
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>
     document.  It covers IP Masquerading for both the 2.0.x and 2.2.x
     kernels and MANY other topics including PPPd, DialD, DHCP, DNS,
     Sendmail, etc.


  ˇ  Make sure that you aren't running ROUTED or GATED.  To verify, run
     "ps aux | grep -e routed -e gated"


  ˇ  Post your question to the IP Masquerade Mailing List (see next the
     FAQ section for details).  Please only use this if you cannot find
     the answer from the IP Masquerading Archive.  Be sure to include
     all the information requested in the ``'' section in your email!!


  ˇ  Post your question to a related Linux NNTP newsgroup.


  ˇ  Send email to ambrose@writeme.com and dranch@trinnet.net.   You
     have a better chance of getting a reply from the IP Masquerading
     Email list than either of us.
  ˇ  Check your configurations again :-)


  7.4.  How do I join or view the IP Masquerade and/or IP Masqurade
  Developers mailing lists and archives?

  There are two ways to join the two Linux IP Masquerading mailing
  lists.  The first way is to send an email to masq-
  request@indyramp.com.  To join the Linux IP Masquerading Developers
  mailing list, send an email to masq-dev-request@indyramp.com.  Please
  see the bullet below for more details.


  ˇ  Subscribe via email:  Now put the word "subscribe" in either the
     subject or body of the e-mail message.  If you want to only
     subscribe to the Digest version of either the main MASQ or MASQ-DEV
     list (all e-mails on the given list during the week are sent to you
     in one big email), put the words "subscribe digest" instead in
     either the subject or body of the e-mail message.

     Once the server receives your request, it will subscribe you to
     your requested list and give you a PASSWORD.  Save this password as
     you will needed to to later unsubscribe from the list or change
     your options.

  The second method is to use a WWW browser and subscribe via a form at
  http://www.indyramp.com/masq-list/ for the main MASQ list or
  http://www.indyramp.com/masq-dev-list/ for the MASQ-DEV list.


  Once subscribed, you will get emails from your subscribed list.  It
  should be also noted that both subscribed and NON-subscribed users can
  access the two list's archives.  To do this, please see the above two
  WWW URLs for more details.

  Lastly, please note that you can only post to the MASQ list from an
  account/address you originally subscribed from.

  If you have any problem regarding the mailing lists or the mailing
  list archive, please contact Robert Novak.

  7.5.  How does IP Masquerade differ from Proxy or NAT services?



  Proxy:  Proxy servers are available for: Win95, NT, Linux, Solaris, etc.

                  Pro:    + (1) IP address ; cheap
                          + Optional caching for better performance (WWW, etc.)

                  Con:    - All applications behind the proxy server must both SUPPORT
                            proxy services (SOCKS) and be CONFIGURED to use the Proxy
                            server
                          - Screws up WWW counters and WWW statistics

           A proxy server uses only (1) public IP address, like IP MASQ, and acts
           as a translator to clients on the private LAN (WWW browser, etc.).
           This proxy server receives requests like TELNET, FTP, WWW,
           etc. from the private network on one interface.  It would then in turn,
           initiate these requests as if someone on the local box was making the
           requests.   Once the remote Internet server sends back the requested
           information, it would re-translate the TCP/IP addresses back to the
           internal MASQ client and send traffic to the internal requesting host.
           This is why it is called a PROXY server.

                  Note:  ANY applications that you might want to use on the
                          internal machines *MUST* have proxy server support
                          like Netscape and some of the better TELNET and FTP
                          clients.  Any clients that don't support proxy servers
                          won't work.

           Another nice thing about proxy servers is that some of them
           can also do caching (Squid for WWW).  So, imagine that you have 50
           proxied hosts all loading Netscape at once.  If they were installed
           with the default homepage URL, you would have 50 copies of the same
           Netscape WWW page coming over the WAN link for each respective computer.
           With a caching proxy server, only one copy would be downloaded by the proxy
           server and then the proxied machines would get the WWW page from the
           cache.  Not only does this save bandwidth on the Internet connection,
           it will be MUCH MUCH faster for the internal proxied machines.



  MASQ:    IP Masq is available on Linux and a few ISDN routers such
   or      as the Zytel Prestige128, Cisco 770, NetGear ISDN routers, etc.
  1:Many
   NAT
                  Pro:    + Only (1) IP address needed (cheap)
                          + Doesn't require special application support
                          + Uses firewall software so your network can become
                            more secure

                  Con:    - Requires a Linux box or special ISDN router
                            (though other products might have this..  )
                          - Incoming traffic cannot access your internal LAN
                            unless the internal LAN initiates the traffic or
                            specific port forwarding software is installed.
                            Many NAT servers CANNOT provide this functionality.
                          - Special protocols need to be uniquely handled by
                            firewall redirectors, etc.  Linux has full support
                            for this (FTP, IRC, etc.) capabilty but many routers
                            do NOT (NetGear DOES).

           Masq or 1:Many NAT is similar to a proxy server in the sense that the
           server will do IP address translating and fake out the remote server
           (WWW for example) as if the MASQ server made the request instead of an
           internal machine.

           The major difference between a MASQ and PROXY server is that MASQ servers
           don't need any configuration changes to all the client machines.  Just
           configure them to use the linux box as their default gateway and everything
           will work fine.  You WILL need to install special Linux modules for things
           like RealAudio, FTP, etc. to work)!

           Also, many people use IP MASQ for TELNET, FTP, etc. *AND* also setup a caching
           proxy on the same Linux box for WWW traffic for the additional performance.


  NAT:     NAT servers are available on Windows 95/NT, Linux, Solaris, and some of the
           better ISDN routers (not Ascend)

                  Pro:    + Very configurable
                          + No special application software needed

                  Con:    - Requires a subnet from your ISP (expensive)

           Network Address Translation is a name for a box that would have a pool of
           valid IP addresses on the Internet interface that it can use.  When on the
           Internal network wanted to goto the Internet, it associates an available
           VALID IP address from the Internet interface to the original requesting PRIVATE
           IP address.  After that, all traffic is re-written from the NAT public IP
           address to the NAT private address.  Once the associated PUBLIC NAT address
           becomes idle for some pre-determined amount of time, the PUBLIC IP address
           is returned back into the public NAT pool.

           The major problem with NAT is, once all of the free public IP addresses are
           used, any additional private users requesting Internet service are out of
           luck until a public NAT address becomes free.



  7.6.  Are there any GUI firewall creation/management tools?


  Yes!  They vary in user interface, complexity, etc. but they are quite
  good though most are only for the IPFWADM tool so far.  Here is a
  short list of available tools in alphabetical order.  If you know of
  any others or have any thoughts on which ones are good/bad/ugly,
  please email David.


  ˇ  John Hardin's IPFWADM Dot file generator - a IPCHAINS version is in
     the works


  ˇ  Sonny Parlin's FWCONFIG
     <http://www.mindstorm.com/~sparlin/fwconfig.shtml> for IPFWADM and
     IPCHAINS


  ˇ  William Stearns's Mason <http://www.pobox.com/~wstearns/mason/> - A
     Build-a-ruleset on-the-fly type system



  7.7.  Does IP Masquerade work with dynamically assigned IP addresses?

  Yes, it works with either dynamic IP addressed assigned by your ISP
  via either PPP or a DHCP/BOOTp server.  As long as you have an valid
  Internet IP address, it should work.  Of course, static IP works too.
  Yet, if you plan on implementing a strong IPFWADM/IPCHAINS ruleset
  and/or plan on using a Port forwarder, your ruleset will have to be
  re-executed everytime your IP address changes.  Please see the top of
  TrinityOS - Section 10
  <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> for
  additional help with strong firewall rulesets and Dynamic IP
  addresses.


  7.8.  Can I use a cable modem (both bi-directional and with modem
  returns), DSL, satellite link, etc. to connect to the Internet and use
  IP Masquerade?


  Yes, as long as Linux supports that network interface, it should work.
  If you receive a dynamic IP address, please see the URL under the
  "Does IP Masquerade work with dynamically assigned IP" FAQ item above.


  7.9.  Can I use Diald or the Dial-on-Demand feature of PPPd with IP
  MASQ?


  Definitely!  IP Masquerading is totally transparent to Diald or PPP.
  The only thing that might become an issue is if you use STRONG
  firewall rulesets with dynamic IP addresses.  See the FAQ item, "Does
  IP Masquerade work with dynamically assigned IP addresses?" above for
  more details.


  7.10.  What applications are supported with IP Masquerade?

  It is very difficult to keep track of a list of "working
  applications".  However, most of the normal Internet applications are
  supported, such as WWW browsing (Netscape, MSIE, etc.), FTP (such as
  WS_FTP), TELNET, SSH, RealAudio, POP3 (incoming email - Pine, Eudora,
  Outlook), SMTP (outgoing email), etc.  A somewhat more complete list
  of MASQ-compatible clients can be found in the ``'' section of this
  HOWTO.

  Applications involving more complicated protocols or special
  connection methods such as video conferencing software need special
  helper tools.

  For more detail, please see the Linux IP masquerading Applications
  <http://www.tsmservices.com/masq> page.


  7.11.  How can I get IP Masquerade running on Redhat, Debian, Slack­
  ware, etc.?

  No matter what Linux distribution you have, the procedures for setting
  up IP Masquerade mentioned in this HOWTO should apply.  Some
  distributions may have GUI or special configuration files that make
  the setup easier.  We try our best to write the HOWTO as general as
  possible.



  7.12.  TELNET connections seem to break if I don't use them often.
  Why is that?

  IP Masq, by default, sets its timers for TCP session, TCP FIN, and UDP
  traffic to 15 minutes.  It is recommend to use the following settings
  (as already shown in this HOWTO's /etc/rc.d/rc.firewall ruleset) for
  most users:

  Linux 2.0.x with IPFWADM:



  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  60 sec timeout for UDP traffic (MASQ'ed ICQ users must enable a 30sec firewall timeout in ICQ itself)
  #
  /sbin/ipfwadm -M -s 7200 10 60



  Linux 2.2.x with IPCHAINS:


  # MASQ timeouts
  #
  #   2 hrs timeout for TCP session timeouts
  #  10 sec timeout for traffic after the TCP/IP "FIN" packet is received
  #  60 sec timeout for UDP traffic (MASQ'ed ICQ users must enable a 30sec firewall timeout in ICQ itself)
  #
  /ipchains -M -S 7200 10 60



  7.13.  When my Internet connection first comes up, nothing works.  If
  I try again, everything then works fine.  Why is this?

  The reason is because you have a dynamic IP address and when your
  Internet connection first comes up, IP Masquerade doesn't know its IP
  address.  There is a solution to this.  In your /etc/rc.d/rc.firewall
  ruleset, add the following:


  # Dynamic IP users:
  #
  #   If you get your IP address dynamically from SLIP, PPP, or DHCP, enable this following
  #       option.  This enables dynamic-ip address hacking in IP MASQ, making the life
  #       with Diald and similar programs much easier.
  #
  echo "1" > /proc/sys/net/ipv4/ip_dynaddr



  7.14.  IP MASQ seems to be working fine but some sites don't work.
  This usually happens with WWW and FTP.

  There is two possible reasons for this.  The first one is VERY common
  and the second is very UNCOMMON.


  ˇ  As of the 2.0.38 and 2.2.9+ Linux kernels, there is a an elusive
     BUG in the Masquerade code that has problems with packets that have
     the DF or "Don't Fragment" bit set.  Basically, when a MASQ box
     connect to the Internet with an MTU of anything less than 1500,
     some packets will have the DF field set.  Though changing the MTU
     1500 on the Linux box will seemingly fix the problem, the bug is
     still there.  What is believed to be happening is that the MASQ
     code is not properly re-writing the returning ICMP packets with the
     ICMP 3 sub 4 code back to the originating MASQed computer.  Because
     of this, the packets get dropped.  If you are a network programmer
     and you think you can fix this.. PLEASE TRY!

     No worries though.  A perfectly good workaround is to change your
     Internet link's MTU to 1500.  Now some users will balk at this
     because it can hurt some latency specific programs like TELNET and
     games but the impact is only slight.  On the flip site, most HTTP
     and FTP traffic will SPEED UP!

     To fix this, first see what your MTU for your Internet link is now.
     To do this, run "/bin/ifconfig".  Now look at the lines that
     corresponds to your Internet connection and look for the MTU.  This
     NEEDs to be set to 1500.  Usually, Ethernet links will default to
     this but PPP will default to 576.


  ˇ  To fix the MTU issue on your PPP link, edit your /etc/ppp/options
     file and towards the top, add the lines "mtu 1500" and "mru 1500".
     Save your new changes and then restart PPP.  Like above, verify
     that your PPP link now has the correct MTU and MTU.


  ˇ  To fix the MTU issue on your Ethernet link to your ADSL,
     Cablemodem, etc, you need to edit your network startup scripts.
     Please see the TrinityOS - Section 16
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> document
     for network optimizations.


  ˇ  Lastly, though this isn't a common problem, some people have found
     this is their solution.  With PPP users, what port is your PPPd
     code connecting to?  A /dev/cua* port or a /dev/ttyS* port?  It
     NEEDS to be a /dev/ttyS* port.  The cua style is OLD and it breaks
     some things in very odd ways.



  7.15.  MASQed FTP clients don't work.

  Check to see that the "ip_masq_ftp" module is loaded.  To do this, log
  into the MASQ server and run the command "/sbin/lsmod".  If you don't
  see the "ip_masq_ftp" module loaded, make sure that you followed the
  BASIC /etc/rc.d/rc.firewall recommendations found in ``'' section.  If
  you are implimenting your own ruleset, make sure you at include most
  of the examples from the HOWTO or you will have lots of continuing
  problems.


  7.16.  IP Masquerading seems slow

  There might be a few reasons for this:

  ˇ  Ethernet attached setups (DSL, Cablemodem, LANs, etc)


  ˇ  Make sure you don't have both your INTERNAL and EXTERNAL networks
     running on the same network card with the "IP Alias" feature.  If
     you ARE doing this, it can be made to work but it will be
     excessively slow due to high levels of collisions, IRQ usage, etc.
     It is highly recommended to get another network card so that the
     internal and external networks have their own interface.

     Make sure you have the right Ethernet settings for both SPEED and
     DUPLEX.


  ˇ  Some 10Mb/s Ethernet cards and most 100Mb/s cards support FULL
     Duplex connections.  Direct connections from Ethernet card to, say,
     DSL modem (without any hubs in between) *CAN* be set to FULL DUPLEX
     but only if the DSL modem supports it.  You should also be sure
     that you have Ethernet cables with all eight wires used and they
     are good quality.

  ˇ  Internal networks that use HUBs -cannot- use Full Duplex.  You need
     either a 10 or 100Mb.s Ethernet SWITCH to be able to do this.

  ˇ  Both auto 10/100Mb/s SPEED negotiation and Full/Half DUPLEX
     negotiation on Ethernet cards can wreck havoc on networks.  I
     recommend to hard code both the NIC speed and duplex into the
     NIC(s) if possible.  This is directly possible via Linux NIC kernel
     modules but isn't directly possible in monolithic kernels.  You
     will need to either use MII utililies from ``'' or hardcode the
     kernel source.


  ˇ  Serial based modem users with PPP


  ˇ  If you have an external modem, make sure you have a good serial
     cable.  Also, many PCs have cheesy ribbon cables connecting the
     serial port from the motherboard or I/O card to the serial port
     connection.  If you have one of these, make sure it is in good
     condition.  Personally, I have ferrite coils (those grey-black
     metal like rings) around ALL of my ribbon cables.


  ˇ  Make sure your MTU is set to 1500 as described in the FAQ section
     of this HOWTO above


  ˇ  Make sure that your serial port is a 16550A or better UART.  Run
     "dmesg | more" to verify


  ˇ  Setup IRQ-Tune for your serial ports


  ˇ  On most PC hardware, the use of Craig Estey's IRQTUNE
     <http://www.best.com/~cae/irqtune/> tool and significantly increase
     serial port performance including SLIP and PPP connections.


  ˇ  Make sure that your serial port for your PPP connection is running
     at 115200 (or faster if both your modem and serial port can handle
     it.. a.k.a  ISDN terminal adapters)


  ˇ  2.0.x kernels:  The 2.0.x kernels are kind of an odd ball because
     you can't directly tell the kernel to clock the serial ports at
     115200.  So, in one of your startup scripts like the
     /etc/rc.d/rc.local or /etc/rc.d/rc.serial file, execute the
     following commands for a modem on COM2:


  ˇ  setserial /dev/ttyS1 spd_vhi


  ˇ  In your PPPd script, edit the actual pppd execution line to include
     the speed "38400" per the pppd man page.


  ˇ  2.2.x kernels:  Unlike the 2.0.x kernels, both the 2.1.x and 2.2.x
     kernels don't have this "spd_vhi" issue.



  ˇ  So, in your PPPd script, edit the actual pppd execution line to
     include the speed "115200" per the pppd man page.


  ˇ  All interface types:


  ˇ  Set the TCP Sliding window to at least 8192


  ˇ  Though this is COMPLETELY out of the scope of this document, this
     helps QUITE A BIT on ANY network link you have be it an internal or
     external PPP, Ethernet, TokenRing, etc. link.  For more details,
     check out the Network Optimization section of TrinityOS - Section
     16 for full details.


  7.17.  Now that I have IP Masquerading up, I'm getting all sorts of
  weird notices and errors in the SYSLOG log files.  How do I read the
  IPFWADM/IPCHAINS firewall errors?

  There is probably two common things that you are going to see:

  ˇ  MASQ: Failed TCP Checksum error:  You will see this error when a
     packet coming from the Internet gets corrupt in the data section of
     the packet but the rest of it "seems" ok.  When the Linux box
     receives this packet, it will calculate the CRC of the packet and
     determine that its corrupt.  On most machines running OSes like
     Microsoft Windows, they just silently drop the packets but Linux IP
     MASQ reports it.  If you get a LOT of them over your PPP link,
     first follow the FAQ entry above for "Masq is slow".


  ˇ  If all of those tips don't help, try adding the line "-vj" to your
     /etc/ppp/options file and restart PPPd.


  ˇ  Firewall hits:  Being on the Internet with a decent firewall, you
     are going to be surprised how many people are going to try to get
     into your Linux box!  So what do all these firewall logs mean?

     From the TrinityOS - Section 10
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri> doc:



             In the below rulesets, any lines that either DENY or REJECT any
             traffic also have a "-o" to LOG this firewall hit to the SYSLOG
             messages file found either in:

                     Redhat:         /var/log
                     Slackware:      /var/adm

             If you look at one of these firewall logs, do would see something like:

             ---------------------------------------------------------------------
             IPFWADM:
             Feb 23 07:37:01 Roadrunner kernel: IP fw-in rej eth0 TCP 12.75.147.174:1633
                100.200.0.212:23 L=44 S=0x00 I=54054 F=0x0040 T=254

             IPCHAINS:
             Packet log: input DENY eth0 PROTO=17 12.75.147.174:1633 100.200.0.212:23
               L=44 S=0x00 I=54054 F=0x0040 T=254
             ---------------------------------------------------------------------

       There is a LOT of information in this just one line.  Lets break out this example
       so refer back to the original firewall hit as you read this.  Please note that this
       example is for IPFWADM though it is DIRECTLY readable for IPCHAINS users.

             --------------

             - This firewall "hit" occurred on "Feb 23 07:37:01"

             - This hit was on the "RoadRunner" computer.

             - This hit occurred on the "IP" or TCP/IP protocol

             - This hit came IN to ("fw-in") the firewall
                     * Other logs can say "fw-out" for OUT or "fw-fwd" for FORWARD

             - This hit was then "rejECTED".
                     * Other logs can say "deny" or "accept"

             - This firewall hit was on the "eth0" interface (Internet link)

             - This hit was a "TCP" packet

             - This hit came from IP address "12.75.147.174" on return port "1633".

             - This hit was addressed to "100.200.0.212" on port "23" or TELNET.
                     * If you don't know that port 23 is for TELNET, look at your
                              /etc/services file to see what other ports are used for.

             - This packet was "44" bytes long

             - This packet did NOT have any "Type of Service" (TOS) set
                     --Don't worry if you don't understand this.. not required to know
                     * divide this by 4 to get the Type of Service for ipchains users

             - This packet had the "IP ID" number of "18"
                     --Don't worry if you don't understand this.. not required to know

             - This packet had a 16bit fragment offset including any TCP/IP packet
               flags of "0x0000"
                     --Don't worry if you don't understand this.. not required to know
                     * A value that started with "0x2..." or "0x3..." means the "More
                       Fragments" bit was set so more fragmented packet will be coming in
                       to complete this one BIG packet.
                     * A value which started with "0x4..." or "0x5..." means that the
                       "Don't Fragment" bit is set.
                     * Any other values is the Fragment offset (divided by 8) to be later
                       used to recombine into the original LARGE packet
             - This packet had a TimeToLive (TTL) of 20.
                     * Every hop over the Internet will subtract (1) from this number.  Usually,
                       packets will start with a number of (255) and if that number ever reaches
                       (0), it means that realistically the packet was lost and will be deleted.



  7.18.  Can I configure IP MASQ to allow Internet users to directly
  contact internal MASQed servers?

  Yes!  With IPPORTFW, you can allow ALL or only a select few Internet
  hosts to contact ANY of your internal MASQed computers.  This topic is
  completely covered in the ``'' section of this HOWTO.



  7.19.  I'm getting "kernel: ip_masq_new(proto=UDP): no free ports." in
  my SYSLOG files.  Whats up?

  One of your internal MASQed machine is creating an abnormally high
  number of packets destined for the Internet.  As the IP Masq server
  builds the MASQ table and forwards these packets out over the
  Internet, the table is quickly filling.  Once the table is full, it
  will give you this error.

  The only application that I known that temporarily creates this
  situation is a gaming program called "GameSpy".  Why?  Gamespy builds
  a server list and then pings all of the servers in the list (1000s of
  game servers).  By creating all these pings, it creates 10,000s of
  quick connections in a VERY short time.  Until these sessions timeout
  via the IP MASQ timeouts, the MASQ tables become "FULL".

  So what can you do about it?  Realistically, don't use programs that
  do things like this.  If you do get this error in your logs, find it
  and stop using it.  If you really like GameSpy, just don't do a lot of
  server refreshes.  Regardless, once you stop running this MASQ'ed
  program, this MASQ error will go away as these connections timeout in
  the MASQ tables.


  7.20.  I'm getting "ipfwadm: setsockopt failed: Protocol not avail­
  able" when I try to use IPPORTFW!

  If you get the error message "ipfwadm: setsockopt failed: Protocol not
  available", you AREN'T running your new kernel.  Make sure that you
  moved the new kernel over, re-run LILO, and then reboot again.

  Please see the end of the ``'' section for full details.


  7.21.  Microsoft File and Print Sharing and Microsoft Domain clients
  (SAMBA) don't work through IP Masq!

  To properly support Microsoft's SMB protocol, a IP Masq module would
  need to be written but there are three viable work-arounds.  For more
  detail, please see this Microsoft KnowledgeBase article.

  The first work-around is to configure IPPORTFW from the ``'' section
  and portfw TCP ports 137, 138, and 139 to the internal Windows
  machine's IP address.  Though this solution works, it will only works
  for ONE internal machine.
  The second solution is to install and configure Samba on the Linux
  MASQ server.  With Samba running, you can then map your internal
  Windows File and Print shares onto the Samba server.  Then, you can
  mount these newly mounted SMB shares to all of your external clients.
  Configuring Samba is fully covered in a HOWTO found in a Linux
  Documentation Project and in the TrinityOS document as well.

  The third solution is to configure a VPN (virtual private network)
  between the two Windows machines or between the two networks.  This
  can either be done via the PPTP or IPSEC VPN solutions.  There is a
  ``'' patch for Linux and also a full IPSEC implimentation available
  for both 2.0.x and 2.2.x kernels.  This solution will probably be the
  most reliable and secure method of all three solutions.

  All of these solutions are NOT covered by this HOWTO.  I recommend
  that you look at the TrinityOS documentation for IPSEC help and JJohn
  Hardin's PPTP page for more information.

  Also PLEASE understand that Microsoft's SMB protocol is VERY insecure.
  Because of this, running either Microsoft File and Print sharing or
  Windows Domain login traffic over the Internet without any encryption
  is a VERY BAD idea.



  7.22.  IRC won't work properly for MASQed IRC users.  Why?

  The main possible reason is because most common Linux distribution's
  IDENT or "Identity" servers can't deal with IP Masqueraded links.  No
  worries though, there are IDENTs out there that will work.

  Installing this software is beyond the scope of this HOWTO but each
  tool has its own documentation.  Here are some of the URLs:

  ˇ  Mident <ftp://ftp.code.org/pub/linux/midentd/> is heavily used by
     most IRC users out there.


  ˇ  Sident <http://insecurity.net/sidentd.gz>


  ˇ  Other Idents including Oidentd
     <ftp://sunsite.unc.edu/pub/Linux/system/network/daemons/>

  Please note that some Internet IRCs servers still won't allow multiple
  connections from the same host even if they get Ident info and the
  users are different though.  Complain to the remote sys admin.  :)


  7.23.  mIRC doesn't work with DCC Sends

  This is a configuration problem on your copy of mIRC.  To fix this,
  first disconnect mIRC from the IRC server.  Now in mIRC, go to File
  --> Setup and click on the "IRC servers tab".  Make sure that it is
  set to port 6667.  If you require other ports, see below.  Next, goto
  File --> Setup --> Local Info and clear the fields for Local Host and
  IP Address.  Now select the checkboxes for "LOCAL HOST" and "IP
  address" (IP address may be checked but disabled).  Next under "Lookup
  Method", configure it for "normal".  It will NOT work if "server" is
  selected.  That's it.  Try to the IRC server again.

  If you require IRC server ports other than 6667, (for example, 6969)
  you need to edit the /etc/rc.d/rc.firewall startup file where you load
  the IRC MASQ modules.  Edit this file and the line for "modprobe
  ip_masq_irc" and add to this line "ports=6667,6969".  You can add
  additional ports as long as they are separated with commas.
  Finally, close down any IRC clients on any MASQed machines and re-load
  the IRC MASQ module:

  /sbin/rmmod ip_masq_irc /etc/rc.d/rc.firewall


  7.24.  Can IP Masquerade work with only ONE Ethernet network card (IP
  Aliasing)?

  Yes and no. With the "IP Alias" kernel feature, users can setup
  multiple aliased interfaces such as eth0:1, eth0:2, etc but its is NOT
  recommended to use aliased interfaces for IP Masquerading.  Why?
  Providing a secure firewall becomes very difficult with a single NIC
  card.  In addition to this, you will experience an abnormal amount of
  errors on this link since incoming packets will almost simultaneously
  be sent out at the same time.  Because of all this and NIC cards now
  cost less than $10, I highly recommend to just get a NIC card for each
  MASQed network segment.

  Users should also understand that IP Masquerading will only work out a
  physical interface such as eth0, eth1, etc.  MASQing out an aliased
  interface such as "eth0:1, eth1:1, etc" will NOT work.  In other
  words, the following WILL NOT WORK:


  ˇ  /sbin/ipfwadm -F -a m -W eth0:1 -S 192.168.0.0/24 -D 0.0.0.0/0

  ˇ  /sbin/ipchains -A forward -i eth0:1 -s 192.168.0.0/24 -j MASQ"

  If you are still interested in using aliased interfaces, you need to
  enable the "IP Alias" feature in the kernel.  You will then need to
  re-compile and reboot.   Once running the new kernel, you need to
  configure Linux to use the new interface (i.e. /dev/eth0:1, etc.).
  After that, you can treat it as a normal Ethernet interface with some
  restrictions like the one above.


  7.25.  I'm trying to use the NETSTAT command to show my Masqueraded
  connections but its not working

  There is a problem with the "netstat" program.  After a Linux reboot,
  running "netstat -M" works fine but after a MASQed computer runs some
  successful ICMP traffic like ping, traceroute, etc., you might see
  something like:


  masq_info.c: Internal Error `ip_masquerade unknown type'.



  The workaround for this is to use the "/sbin/ipfwadm -M -l" command.
  You will also notice that once the listed ICMP masquerade entries
  timeout, "netstat" works again.



  7.26.  I would like to get Microsoft PPTP (GRE tunnels) and/or IPSEC
  (Linux SWAN) tunnels running through IP MASQ

  This IS possible.  Though it is somewhat out of the scope of this
  document, check out John Hardin's PPTP Masq page for all the details.



  7.27.  I want to get the XYZ network game to work through IP MASQ but
  it won't work.  Help!

  First, check Steve Grevemeyer's MASQ Applications page
  <http://www.tsmservices.com/masq>.  If your solution isn't listed
  there, try patching your Linux kernel with Glenn Lamb's LooseUDP
  <ftp://ftp.netcom.com/pub/mu/mumford/loose-udp-2.0.36.patch.gz> patch
  which is covered in the ``'' section above.  Also check out Dan
  Kegel's NAT Page <http://www.alumni.caltech.edu/~dank/peer-nat.html>
  for more information.

  If you are technically inclined, use the program "tcpdump" and sniff
  your network.  Try to find out what protocols and port numbers your
  XYZ game is using.  With this information in hand, subscribe to the IP
  Masq email list and email your results for help.


  7.28.  IP MASQ works fine for a while but then it stops working.  A
  reboot seems to fix this for a while.  Why?

  I bet you are using IPAUTOFW and/or you have it compiled into the
  kernel huh??  This is a known problem with IPAUTOFW.  It is recommend
  to NOT even configure IPAUTOFW into the Linux kernel and use IPPORTFW
  option instead.  This is all covered in more detail in the ``''
  section.


  7.29.  Internal MASQed computers cannot send SMTP or POP-3 mail!


  Though this isn't a Masquerading issue per se but many people do this
  so it should be mentioned.

  SMTP:  The issue is that you are probably using your Linux box as a
  SMTP relay server and get the following error:


       "error from mail server: we do not relay"


  Newer versions of Sendmail and other Mail Transfer Agents (MTAs) dis­
  able relaying by default (this is a good thing).  So do the following
  to fix this:


  ˇ  Sendmail:  Enable specific relaying for your internal MASQed
     machines by editing the /etc/sendmail.cw file and add the hostname
     and domain name of your internal MASQed machine.  You should also
     check to see that the /etc/hosts file has the IP address and Fully
     Qualified Domain Name (FQDN) configured in it.  Once this is done,
     you need to restart Sendmail for it to re-read its configuration
     files.  This is covered in TrinityOS - Section 25
     <http://www.ecst.csuchico.edu/~dranch/LINUX/TrinityOS.wri>

  POP-3:  Some users configure their internal MASQ'ed computer's POP-3
  clients to connect to some external SMTP server.  While this is fine,
  many SMTP servers out there will try to IDENT your connection on port
  113.  Most likely your problem stems around your default Masquerade
  policy being set to DENY.  This is BAD.  Set it to REJECT and re-run
  your rc.firewall ruleset.


  7.30.  I need different internal MASQed networks to exit on different
  external IP addresses (IPROUTE2)


  Say you have the following problem:

  LAN ----------> official IP 192.168.1.x --> 123.123.123.11 192.168.2.x
  -->123.123.123.12


  You have to first understand that both IPFWADM and IPCHAINS run
  *AFTER* the routing system has decided where to send a packet.  This
  ought to be stamped in big red letters on all IPFWADM/IPCHAINS/IPMASQ
  documentation.  You will need to get your routing right first and then
  add IPFWADM/IPCHAINS and/or Masq.

  In the case shown above, you need to persuade the routing system to
  direct packets from 192.168.1.x via 123.123.1233.11 and packets from
  192.168.2.x via 123.123.123.12.  That is the hard part and adding Masq
  on top of correct routing is easy.

  To do this fancy routing, you will use IPROUTE2.

  Primary FTP site is:


  ˇ  ftp://ftp.inr.ac.ru/ip-routing

     Mirrors are:

     ftp://linux.wauug.org/pub/net
     ftp://ftp.nc.ras.ru/pub/mirrors/ftp.inr.ac.ru/ip-routing/
     ftp://ftp.gts.cz/MIRRORS/ftp.inr.ac.ru/
     ftp://ftp.funet.fi/pub/mirrors/ftp.inr.ac.ru/ip-routing/ (STM1 to
     USA) ftp://sunsite.icm.edu.pl/pub/Linux/iproute/
     ftp://ftp.sunet.se/pub/Linux/ip-routing/
     ftp://ftp.nvg.ntnu.no/pub/linux/ip-routing/
     ftp://ftp.crc.ca/pub/systems/linux/ip-routing/ ftp://ftp.paname.org
     (France) ftp://donlug.ua/pub/mirrors/ip-route/
     ftp://omni.rk.tusur.ru/mirrors/ftp.inr.ac.ru/ip-routing/

     RPMs are available at ftp://omni.rk.tusur.ru/Tango/ and at
     ftp://ftp4.dgtu.donetsk.ua/pub/RedHat/Contrib-Donbass/KAD/


  NOTE:  The following instructions are given below ONLY because
  currently there is very little documentation to the IPROUTE2 tool
  available.  Check out http://www.compendium.com.ar/policy-routing.txt
  for the beginnings of a IPROUTE2 howto.


  The "iprule" and "iproute" commands are the same as "ip rule" and "ip
  route" commands (I prefer the former since it is easier to search
  for.)  All the commands below are completely untested, if they do not
  work, please contact the author of IPROUTE2.. not David Ranch  or
  anyone on the Masq email list as it has NOTHING to do with IP
  Masquerading.

  The first few commands only need to be done once at boot, say in
  /etc/rc.d/rc.local file.



  # Allow internal LANs to route to each other, no masq.
    /sbin/iprule add from 192.168.0.0/16 to 192.168.0.0/16 table main pref 100
  # All other traffic from 192.168.1.x is external, handle by table 101
    /sbin/iprule add from 192.168.1.0/24 to 0/0 table 101 pref 102
  # All other traffic from 192.168.2.x is external, handle by table 102
    /sbin/iprule add from 192.168.2.0/24 to 0/0 table 102 pref 102

  These commands need to be issued when eth0 is configured, perhaps in
  /etc/sysconfig/network-scripts/ifup-post (for Redhat systems).  Be sure to
  do them by hand first to make sure they work.

  # Table 101 forces all assigned packets out via 123.123.123.11
    /sbin/iproute add table 101 via 62123.123.123.11
  # Table 102 forces all assigned packets out via 123.123.123.12
    /sbin/iproute add table 102 via 62123.123.123.12

  At this stage, you should find that packets from 192.168.1.x to the
  outside world are being routed via 123.123.123.11, packets from
  192.168.2.x are routed via 123.123.123.12.

  Once routing is correct, now you can add any IPFWADM or IPCHAINS rules.
  The following examples are for IPCHAINS:


  /sbin/ipchains -A forward -i ppp+ -j MASQ

  If everything hangs together, the masq code will see packets being
  routed out on 123.123.123.11 and 123.123.123.12 and will use those addresses
  as the masq source address.



  7.31.  Why do the new 2.1.x and 2.2.x kernels use IPCHAINS instead of
  IPFWADM?

  IPCHAINS supports the following features that IPFWADM doesn't:


  ˇ  "Quality of Service" (QoS  support)


  ˇ  A TREE style chains system vs. LINEAR system like IPFWADM  (Eg.
     this allows something like "if it is ppp0, jump to this chain
     (which contains its own difference set of rules)"


  ˇ  IPCHAINS is more flexible with configuration.  For example, it has
     the "replace" command (in addition to "insert" and "add").  You can
     also negate rules (e.g. "discard any outbound packets that don't
     come from my registered IP" so that you aren't the source of
     spoofed attacks).


  ˇ  IPCHAINS can filter any IP protocol explicitly, not just TCP, UDP,
     ICMP


  7.32.  I've just upgraded to the 2.2.x kernels, why isn't IP Masquer­
  ade working?

  There are several things you should check assuming your Linux IP Masq
  box already have proper connection to the Internet and your LAN:


  ˇ  Make sure you have the necessary features and modules are compiled
     and loaded.  See earlier sections for detail.


  ˇ  Check /usr/src/linux/Documentation/Changes and make sure you have
     the minimal requirement for the network tools installed.


  ˇ  Make sure you followed all the tests in the ``'' section of the
     HOWTO.


  ˇ  You should use ipchains <http://www.rustcorp.com/linux/ipchains/>
     to manipulate IP Masq and firewalling rules.


  ˇ  The standard IPAUTOFW and IPPORTFW port forwarders have been
     replaced by IPMASQADM <http://juanjox.kernelnotes.org/>.  You'll
     need to apply these patches to the kernel, re-compile the kernel,
     compile the new IPMASQADM tool and then convert your old
     IPAUTOFW/IPPORTFW firewall rulesets to the new syntax.  This is
     completely covered in the ``'' section.


  ˇ  Go through all setup and configuration again!  A lot of time it's
     just a typo or a simple mistake you are overlooking.


  7.33.  I've just upgraded to a 2.0.38+ kernels later, why isn't IP
  Masquerade working?

  There are several things you should check assuming your Linux IP Masq
  box already have proper connection to the Internet and your LAN:


  ˇ  Make sure you have the necessary features and modules are compiled
     and loaded.  See earlier sections for detail.


  ˇ  Check /usr/src/linux/Documentation/Changes and make sure you have
     the minimal requirement for the network tools installed.


  ˇ  Make sure you followed all the tests in the ``'' section of the
     HOWTO.


  ˇ  You should use ipfwadm <http://www.xos.nl/> to manipulate IP Masq
     and firewalling rules.  If you want to use IPCHAINS, you'll need to
     apply a patch the 2.0.x kernels.


  ˇ  Go through all setup and configuration again!  A lot of time it's
     just a typo or a simple mistake you overlooked.


  7.34.  I need help with EQL connections and IP Masq

  EQL has nothing to do with IP Masq though they are commonly teamed up
  on Linux boxes.  Because of this, I recommend to check out the NEW
  version of Robert Novak's EQL HOWTO for all your EQL needs.



  7.35.  I can't get IP Masquerade to work!  What options do I have for
  Windows Platforms?

  Giving up a free, reliable, high performance solution that works on
  minimal hardware and pay a fortune for something that needs more
  hardware, lower performance and less reliable?  (IMHO.  And yes, I
  have real life experience with these ;-)

  Okay, it's your call.  If you want a Windows NAT and/or proxy
  solution, here is a decent listing.  I have no preference of these
  tools since I haven't used them before.


  ˇ  Firesock (from the makers of Trumpet Winsock)

  ˇ  Does Proxy

  ˇ  http://www.trumpet.com.au



  ˇ  Iproute

  ˇ  DOS program designed to run on 286+ class computers

  ˇ  requires another box like Linux MASQ

  ˇ  http://www.mischler.com/iproute/



  ˇ  Microsoft Proxy

  ˇ  Requires Windows NT Server

  ˇ  Quite expensive

  ˇ  http://www.microsoft.com



  ˇ  NAT32

  ˇ  Windows 95/98/NT compatible

  ˇ  http://www.nat32.com

  ˇ  Roughly $25 for Win9x and $47 for Win9x and WinNT



  ˇ  SyGate

  ˇ  http://www.sygate.com



  ˇ  Wingate

  ˇ  Does proxy

  ˇ  Costs roughly $30 for 2-3 IPs

  ˇ  http://www.wingate.com


  ˇ  Winroute

  ˇ  Does NAT

  ˇ  http://www.winroute.cz/en/


  Lastly, do a web search on "MS Proxy Server", "Wingate", "WinProxy",
  or goto www.winfiles.com <http://www.winfiles.com>.  And definitely
  DON'T tell anyone that we sent you.


  7.36.  I want to help on IP Masquerade development.  What can I do?

  Join the Linux IP Masquerading DEVELOPERS list and ask the developers
  there what you can help with.  For more details on joining the lists,
  check out the ``'' FAQ section.

  Please DON'T ask NON-IP-Masquerade development related questions
  there!!!!


  7.37.  Where can I find more information on IP Masquerade?

  You can find more information on IP Masquerade at the Linux IP
  Masquerade Resource <http://ipmasq.cjb.net/> that David Ranch
  maintains.

  You can also find more information at Dranch's Linux page
  <http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html> where
  the TrinityOS and other Linux documents are kept.

  You may also find more information at The Semi-Original Linux IP
  Masquerading Web Site <http://www.indyramp.com/masq/> maintained by
  Indyramp Consulting, who also provides the IP Masq mailing lists.

  Lastly, you can look for specific questions in the IP MASQ and IP MASQ
  DEV email archives or ask a specific question on these lists.  Check
  out the ``'' FAQ item for more details.


  7.38.  I want to translate this HOWTO to another language, what should
  I do?

  Make sure the language you want to translate to is not already covered
  by someone else.  But, most of the translated HOWTOs are now OLD and
  need to be updated.  A list of available HOWTO translations are
  available at the Linux IP Masquerade Resource
  <http://ipmasq.cjb.net/>.

  If a copy of a current IP MASQ HOWTO isn't in your proposed language,
  please download the newest copy of the IP-MASQ HOWTO SGML code from
  the Linux IP Masquerade Resource <http://ipmasq.cjb.net/>.  From
  there, begin your work while maintaining good SGML coding.  For more
  help on SGML, check out www.sgmltools.org <http://www.sgmltools.org>


  7.39.  This HOWTO seems out of date, are you still maintaining it?
  Can you include more information on ...?  Are there any plans for mak­
  ing this better?

  Yes, this HOWTO is still being maintained.  In the past, we've been
  guilty of being too busy working on two jobs and don't have much time
  to work on this, my apology.  As of v1.50, David Ranch has begun to
  revamp the document and get it current again.

  If you think of a topic that could be included in the HOWTO, please
  send email to ambrose@writeme.com and dranch@trinnet.net.  It will be
  even better if you can provide that information.  We will then include
  the information into the HOWTO once it is both found appropriate and
  tested.  Many thanks for your contributions!

  We have a lot of new ideas and plans for improving the HOWTO, such as
  case studies that will cover different network setup involving IP
  Masquerade, more on security via strong IPFWADM/IPCHAINS firewall
  rulesets, IPCHAINS usage, more FAQ entries, etc.  If you think you can
  help, please do!  Thanks.


  7.40.  I got IP Masquerade working, it's great!  I want to thank you
  guys, what can I do?


  ˇ  Can you translate the newer version of the HOWTO to another
     language?

  ˇ  Thank the developers and appreciate the time and effort they spent
     on this.

  ˇ  Join the IP Masquerade email list and support new MASQ users

  ˇ  Send an email to us and let us know how happy you are

  ˇ  Introduce other people to Linux and help them when they have
     problems.


  8.  Miscellaneous



  8.1.  Useful Resources


  ˇ  IP Masquerade Resource page <http://ipmasq.cjb.net/> Will have all
     the current information for setting up IP Masquerade on 2.0.x,
     2.2.x, and even old 1.2 kernels!


  ˇ  Juan Jose Ciarlante's WWW site <http://juanjox.kernelnotes.org> who
     is the current Linux IP Masquerade maintainer.


  ˇ  IP Masquerade mailing list Archives
     <http://www.indyramp.com/lists/masq> contains the recent messages
     sent to the mailing lists.


  ˇ  David Ranch's Linux page including the TrinityOS Linux document and
     current versions of the IP-MASQ-HOWTO.
     <http://www.ecst.csuchico.edu/~dranch/LINUX/index-linux.html>.
     Topics such as IP MASQ, strong IPFWADM/IPCHAINS rulesets, PPP,
     Diald, Cablemodems, DNS, Sendmail, Samba, NFS, Security, etc. are
     covered.


  ˇ  The IP Masquerading Applications page
     <http://www.tsmservices.com/masq>: A comprehensive list of
     applications that work or can be tuned to work through a Linux IP
     masquerading server.


  ˇ  For people setting up IP Masq on MkLinux, email Taro Fukunaga at
     tarozax@earthlink.net for a copy of his short MkLinux version of
     this HOWTO.


  ˇ  IP masquerade FAQ <http://www.indyramp.com/masq/ip_masquerade.txt>
     has some general information


  ˇ  Paul Russel's http://www.rustcorp.com/linux/ipchains/ doc and its
     possibly older backup at Linux IPCHAINS HOWTO.  This HOWTO has lots
     of information for IPCHAINS usage, as well as source and binaries
     for the ipchains tool.


  ˇ  X/OS Ipfwadm page <http://www.xos.nl/linux/ipfwadm/> contains
     sources, binaries, documentation, and other information about the
     ipfwadm package


  ˇ  Check out the GreatCircle's Firewall mailing list for a great
     resource for strong firewall rulesets.


  ˇ  The LDP Network Administrator's Guide
     <http://metalab.unc.edu/mdw/LDP/nag/nag.html> is a MUST for the
     beginner Linux administrator trying to set up a network.


  ˇ  The Linux NET-3 HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/NET-3-HOWTO.html> is also another
     comprehensive document on how to setup and configure Linux
     networking.


  ˇ  Linux ISP Hookup HOWTO <http://metalab.unc.edu/mdw/HOWTO/ISP-
     Hookup-HOWTO.html> and Linux PPP HOWTO
     <http://metalab.unc.edu/mdw/HOWTO/PPP-HOWTO.html> gives you
     information on how to connect your Linux host to the Internet


  ˇ  Linux Ethernet-Howto <http://metalab.unc.edu/mdw/HOWTO/Ethernet-
     HOWTO.html> is a good source of information about setting up a LAN
     running over Ethernet.


  ˇ  Donald Becker's NIC drivers and Support Utils
     <http://cesdis.gsfc.nasa.gov/linux/drivers/>


  ˇ  You may also be interested in Linux Firewalling and Proxy Server
     HOWTO <http://metalab.unc.edu/mdw/HOWTO/Firewall-HOWTO.html>


  ˇ  Linux Kernel HOWTO <http://metalab.unc.edu/mdw/HOWTO/Kernel-
     HOWTO.html> will guide you through the kernel compilation process


  ˇ  Other Linux HOWTOs <http://metalab.unc.edu/mdw/HOWTO/HOWTO-
     INDEX-3.html> such as Kernel HOWTO


  ˇ  Posting to the USENET newsgroup: comp.os.linux.networking



  8.2.  Linux IP Masquerade Resource


  The Linux IP Masquerade Resource  <http://ipmasq.cjb.net/> is a
  website dedicated to Linux IP Masquerade information also maintained
  by Ambrose Au.  It has the latest information related to IP Masquerade
  and may have information that is not being included in the HOWTO.

  You may find the Linux IP Masquerade Resource at the following
  locations:

  ˇ  http://ipmasq.cjb.net/, Primary Site, redirected to
     http://ipmasq.cjb.net/


  ˇ  http://ipmasq2.cjb.net/, Secondary Site, redirected to
     http://www.geocities.com/SiliconValley/Heights/2288/



  8.3.  Thanks to the following people..


  In Alphabetical order:

  ˇ  Gabriel Beitler, gabrielb@voicenet.com
     on providing section 3.3.8 (setting up Novell)


  ˇ  Juan Jose Ciarlante, irriga@impsat1.com.ar
     on contributing his work on his IPMASQADM port forward tool, his
     work on the 2.1.x and 2.2.x kernel code, the original LooseUDP
     patch, etc.


  ˇ  Steven Clarke, steven@monmouth.demon.co.uk
     on contributing his IPPORTFW IP port forwarder tool


  ˇ  Andrew Deryabin, djsf@usa.net
     on contributing his ICQ MASQ module


  ˇ  Ed Doolittle, dolittle@math.toronto.edu
     on suggestion to -V option in ipfwadm command for improved security


  ˇ  Matthew Driver, mdriver@cfmeu.asn.au
     on helping extensively on this HOWTO, and providing section 3.3.1
     (setting up Windows 95)


  ˇ  Ken Eves, ken@eves.com
     on the FAQ that provides invaluable information for this HOWTO


  ˇ  John Hardin, jhardin@wolfenet.com
     for his PPTP and IPSEC forwarding tools


  ˇ  Glenn Lamb, mumford@netcom.com
     for the LooseUDP patch


  ˇ  Ed. Lott, edlott@neosoft.com
     for a long list of tested system and software
  ˇ  Nigel Metheringham, Nigel.Metheringham@theplanet.net
     on contributing his version of IP Packet Filtering and IP
     Masquerading HOWTO, which make this HOWTO a better and technical
     in-depth document
     section 4.1, 4.2, and others


  ˇ  Keith Owens, kaos@ocs.com.au
     on providing an excellent guide on ipfwadm section 4.2
     on correction to ipfwadm -deny option which avoids a security hole,
     and clarified the status of ping over IP Masquerade


  ˇ  Michael Owings, mikey@swampgas.com
     on providing section for CU-SeeMe and Linux IP-Masquerade Teeny
     How-To


  ˇ  Rob Pelkey, rpelkey@abacus.bates.edu
     on providing section 3.3.6 and 3.3.7 (setting up MacTCP and Open
     Transport)


  ˇ  Harish Pillay, h.pillay@ieee.org
     on providing section 4.5 (dial-on-demand using Diald)


  ˇ  Mark Purcell, purcell@rmcs.cranfield.ac.uk
     on providing section 4.6 (IPautofw)


  ˇ  David Ranch, dranch@trinnet.net
     help updating and maintaining this HOWTO and the Linux IP
     Masquerade Resource Page, the TrinityOS document , ..., too many to
     list here :-)


  ˇ  Paul Russell, rusty@rustcorp.com.au
     for all his work on IP CHAINS, IP Masquerade kernel patches, etc


  ˇ  Ueli Rutishauser, rutish@ibm.net
     on providing section 3.3.9 (setting up OS/2 Warp)


  ˇ  Steve Grevemeyer, grevemes@tsmservices.com
     for taking over the IP Masq Applications page from Lee Nevo and
     updating it to a full DB backend.


  ˇ  Fred Viles, fv@episupport.com


  ˇ  John B. (Brent) Williams, forerunner@mercury.net
     on providing section 3.3.7 (setting up Open Transport)


  ˇ  Enrique Pessoa Xavier, enrique@labma.ufrj.br
     on the BOOTp setup suggestion


  ˇ  All the people on the IP-MASQ email list, masq@tiffany.indyramp.com
     for their help and support for all the new Linux MASQ users.



  ˇ  Other code and documentation developers of IP Masquerade for this
     great feature



       ˇ  Delian Delchev, delian@wfpa.acad.bg

       ˇ  David DeSimone (FuzzyFox), fox@dallas.net

       ˇ  Jeanette Pauline Middelink, middelin@polyware.iaf.nl

       ˇ  Miquel van Smoorenburg, miquels@q.cistron.nl

       ˇ  Jos Vos, jos@xos.nl

       ˇ  And more who I may have failed to mention here (please
          let me know)



  ˇ  All users sending feedback and suggestion to the mailing list,
     especially the ones who reported errors in the document and the
     clients that are supported and not supported


  ˇ  We apologize if we have omitted any important names, not included
     information that some fellow users have sent us yet, etc.  There
     are many suggestions and ideas sent but there isn't have enough
     time to verify and integrate these changes.  David Ranch is
     constantly trying his best to incorporate all the information sent
     to me into the HOWTO.  I thank you for the effort, and I hope you
     understand our situation.



  8.4.  Reference


  ˇ  Original IP masquerade FAQ by Ken Eves

  ˇ  IP masquerade mailing list archive by Indyramp Consulting

  ˇ  IP Masquerade WWW site by Ambrose Au

  ˇ  Ipfwadm page by X/OS

  ˇ  Various networking related Linux HOWTOs

  ˇ  Some topics covered in TrinityOS by David Ranch


  8.5.  Changes


  ˇ  TO do - HOWTO:

  ˇ  Add the scripted IPMASQADM example to the Forwarders section.  Also
     confirm the syntax.

  ˇ  Add a little section on having multiple subnets behind a MASQ
     server

  ˇ  Confirm the IPCHAINS ruleset and make sure it is consistant with
     the IPFWADM ruleset


     TO DO - WWW page:

  ˇ  Update all PPTP urls from lowrent to
     ftp://ftp.rubyriver.com/pub/jhardin/masquerade/ip_masq_vpn.html

  ˇ  Update the PPTP patch on the masq site

  ˇ  Update the portfw FTP patch

     Changes from 1.82 to 1.85 - 05/29/00

  ˇ  Ambrose Au's name has been taken off the title page as DAvid Ranch
     has been the primary maintainer for the HOWTO for over a year.
     Ambrose will still be involved with the WWW site though.

  ˇ  Deleted a stray SPACE in section 6.4

  ˇ  Re-ordered the compatible MASQ'ed OS section and added instructions
     for setting up a AS/400 system running on OS/400.  Thanks to
     jaco@libero.it for the notes.

  ˇ  Added an additional PORFW-FTP patch URL for FTP access if HTTP
     access fails.

  ˇ  Updated the kernel versions for Redhat 5.1 & 6.1 in the FAQ

  ˇ  Added FloppyFW to the list of MASQ-enabled Linux distros

  ˇ  Fixed an issue in the Stronger IPFWADM rule set where there were
     spaces between "ppp_ip" and the "=".

  ˇ  In the kernel compiling section for 2.2.x kernels, I removed the
     reference to enable "CONFIG_IP_ALWAYS_DEFRAG".  This option was
     removed from the compiling section and enabled by default with MASQ
     enabled in 2.2.12.

  ˇ  Because of the above change in the kernel behavior, I have added
     the enabling of ip_always_defrag to all the rc.firewall examples.

  ˇ  Updated the status of support for H.323.  There is now ALPHA
     versions of modules to support H.323 on both 2.0.x and 2.2.x
     kernels.

  ˇ  Added Debian v2.2 to the supported MASQ distributions list

  ˇ  Fixed a long standing issue where the section that covered explict
     filtering of IP addresses for IPCHAINS had old IPFWADM syntax.
     I've also cleaned this section up a little and made it a little
     more understandable.

  ˇ  Doh!  Added Juan Ciarlante's URL to the important MASQ resources
     section.  Man.. you guys need to make me more honest than this!!

  ˇ  Updated the HOWTO to reflect kernels 2.0.38 and 2.2.15

  ˇ  Rerversed the order shown to compile kernels to show 2.2.x kernels
     first as 2.0.x is getting pretty old.

  ˇ  Updated the 2.2.x kernel compiling section to reflect the changed
     options for the latter 2.2.x kernels.

  ˇ  Added a a possible solution for people that fail to get past MASQ
     test #5.

     Changes from 1.81 to 1.82 - 01/22/00

  ˇ  Added a missing subsection for /proc/sys/net/ipv4/ip_dynaddr in the
     stronger IPCHAINS ruleset.  Section 6.5

  ˇ  Changed the IP Masq support for Debian 2.1 to YES

  ˇ  Reorganized and updated the "Masq is slow" FAQ section to include
     fixing Ethernet speed and duplex issues.

  ˇ  Added a link to Donald Becker's MII utilities for Ethernet NIC
     cards

  ˇ  Added a missing ")" for the 2.2.x section (previously fixed it only
     for the 2.0.x version) to the ICQ portfw script and changed the
     evaluation from -lt to -le

  ˇ  Added Caldera eServer v2.3 to the MASQ supported list

  ˇ  Added Mandrake 6.0, 6.1, 7.0 to the MASQ supported list

  ˇ  Added Slackware v7.0 to the MASQ supported list

  ˇ  Added Redhat 6.1 to the MASQ supported list

  ˇ  Added TurboLinux 4.0 Lite to the MASQ supported list

  ˇ  Added SuSe 6.3 to the MASQ supported list

  ˇ  Updated the recommended stable 2.2.x kernel to be anything newer
     than 2.2.11

  ˇ  In section 3.3, the HOWTO forgot how to tell the user how to load
     the /etc/rc.d/rc.firewall upon each reboot.  This has now been
     covered for Redhat (and Redhat-based distros) and Slackware.

  ˇ  Added clarification in the Windows WFWG v3.x and NT setup sections
     why users should NOT configure the DHCP, WINS, and Forwarding
     options.

  ˇ  Added a FAQ section on how to fix FTP problems with MASQed
     machines.

  ˇ  Fixed a typo in the Stronger firewall rulesets.  The "extip"
     variabl cannot have the SPACE between the variable name and the "="
     sign.  Thanks to johnh@mdscomp.com for the sharp eye.

  ˇ  Updated the compatibly section:  Mandrake 7.0 is based on 2.2.14
     and TurboLinux v6.0 runs 2.2.12

     Changes from 1.80 to 1.81 - 01/09/00

  ˇ  Updated the ICQ section to reflect that the new ICQ Masq module
     supports file transfer and real-time chat.  The 2.0.x module still
     has those limitations.

  ˇ  Updated Steven E. Grevemeyer's email address.  He is the maintainer
     of the IP Masq Applications page.

  ˇ  Fixed a few lines that were missing the work AREN'T for the
     "setsockopt" errors.

  ˇ  Updated a error the strong IPCHAINS ruleset where it was using the
     variable name "ppp_ip" instead of "extip".

  ˇ  Fixed a "." vs a "?" typo in section 3.3.1 in the DHCP comment
     section.

  ˇ  Added a missing ")" to the ICQ portfw script and changed the
     evaluation from -lt to -le

  ˇ  Updated the Quake Module syntax to NOT use the "ports=" verbage



     Changes from 1.79 to 1.80 - 12/26/99

  ˇ  Fixed a space typo when setting the "ppp_ip" address.

  ˇ  Fixed a typo in the simple IPCHAINS ruleset.  "deny" to "DENY"

  ˇ  Updated the URLs for Bjorn's "modutils" for Linux

  ˇ  Added verbage about NetFilter and IPTables and gave URLs until it
     is added to this HOWTO or a different HOWTO.

  ˇ  Updated the simple /etc/rc.d/rc.firewall examples to notify users
     about the old Quake module bug.

  ˇ  Updated the STRONG IPFWADM /etc/rc.d/rc.firewall to clarify users
     about dynamic IP addresses (PPP & DHCP), newer DHCPCD syntax, and
     the old Quake module bug.

  ˇ  Updated the STRONG IPCHAINS /etc/rc.d/rc.firewall to ADD a missing
     section on dynamic IP addresses (PPP & DHCP) and the old Quake
     module bug.

  ˇ  Added a note in the "Applications that DO NOT work" section that
     there IS a beta module for Microsoft NetMeeting (H.323 based) v2.x
     on 2.0.x kernels.  There is NO versions available for Netmeeting
     3.x and/or 2.2.x kernels as of yet.



     Changes from 1.78 to 1.79 - 10/21/99

  ˇ  Updated the HOWTO name to reflect that it isn't a MINI anymore!

     Changes from 1.77 to 1.78 - 8/24/99

  ˇ  Fixed a typeo in "Section 6.6 - Multiple Internal Networks" where
     the -a policy was ommited.

  ˇ  Deleted the 2.2.x kernel configure option "Drop source routed
     frames" since it is now enabled by default and the kernel compile
     option was removed.

  ˇ  Updated the 2.2.x and all other IPCHAINS sections to notify users
     of the IPCHAINS fragmentation bug.

  ˇ  Updated all the URLs point at Lee Nevo's old IP Masq Applications
     page to Seg's new page.

     Changes from 1.76 to 1.77 - 7/26/99

  ˇ  Fixed a typo in the Port fowarding section that used "ipmasqadm
     ipportfw -C" instead of "ipmasqadm portfw -f"

     Changes from 1.75 to 1.76 - 7/19/99

  ˇ  Updated the "ipfwadm: setsockopt failed: Protocol not available"
     message in the FAQ to be more clear instead of making the user hunt
     for the answer in the Forwarders section.

  ˇ  Fixed incorrect syntax in section 6.7 for IPMASQADM and "portfw"

     Changes from 1.72 to 1.75 - 6/19/99

  ˇ  Fixed the quake module port setup order for the weak IPFWADM &
     IPCHAINS ruleset and the strong IPFWADM ruleset as well.

  ˇ  Added a user report about port forwarding ICQ 4000 directly in and
     using ICQ's default settings WITHOUT enabling the "Non-Sock" proxy
     setup.

  ˇ  Updated the URLs for the IPMASQADM tool

  ˇ  Added references to Taro Fukunaga, tarozax@earthlink.net for his
     MkLinux port of the HOWTO

  ˇ  Updated the blurb about Sonny Parlin's FWCONFIG tool to note new
     IPCHAINS support

  ˇ  Noted that Fred Vile's patch for portfw'ed FTP access is ONLY
     available for the 2.0.x kernels

  ˇ  Updated the 2.2.x kernel step with a few clarifications on the
     Experiemental tag

  ˇ  Added Glen Lamb's name to the credits for the LooseUDP patch

  ˇ  Added a clarification on installing the LooseUDP patch that it
     should use "cat" for non-compressed patches.

  ˇ  Fixed a typo in the IPAUTO FAQ section

  ˇ  I had the DHCP client port numbers reversed for the IPFWADM and
     IPCHAINS rulesets.  The order I had was if your Linux server was a
     DHCP SERVER.

  ˇ  Added explict /sbin path to all weak and strong ruleset examples.

  ˇ  Made some clarifications in the strong IPFWADM section regarding
     Dynamic IP addresses for PPP and DHCP users.  I also noted that the
     strong rulesets should be re-run when PPP comes up or when a DHCP
     lease is renewed.

  ˇ  Added reference in the 2.2.x requirements, updated the ICQ FAQ
     section, and added Andrew Deryabin to credits section for his ICQ
     MASQ module.

  ˇ  Added some clarifcation in the FAQ section why the 2.1.x and 2.2.x
     kernels went to IPCHAINS.

  ˇ  Added a little FAQ section on Microsoft File/Print/Domain services
     (Samba) through a MASQ server.  I also added a URL to a Microsoft
     Knowledge base document for more details.

  ˇ  Added clarification in the FAQ section that NO Debian distribution
     supports IP masq out of the box.

  ˇ  Updated the supported MASQ distributions in the FAQ section.

  ˇ  Added to the Aliased NIC section of the FAQ that you CANNOT masq
     out of an aliased interface.

  ˇ  Wow.. never caught this before but the "ppp-ip" variable in the
     strong ruleset section is an invalid variable name!  It has been
     renamed to "ppp_ip"

  ˇ  In both the IPFWADM and IPCHAINS simple ruleset setup areas, I had
     a commented out section on enabling DHCP traffic.  Problem is, it
     was below the final reject line!  Doh!  I moved both up a section.

  ˇ  In the simple IPCHAINS setup, the #ed out line for DHCP users, I
     was using the IPFWADM "-W" command instead of IPCHAINS's "-i"
     parameter.

  ˇ  Added a little blurb to the Forwarders section the resolution to
     the famous "ipfwadm: setsockopt failed: Protocol not available"
     error.  This also includes a little /proc test to let people
     confirm if IPPORTFW is enabled in the kernel.  I also added this
     error to a FAQ section for simple searching.

  ˇ  Added a Strong IPCHAINS ruleset to the HOWTO

  ˇ  Added a FAQ section explaining the "kernel: ip_masq_new(proto=UDP):
     no free ports." error.

  ˇ  Added an example of scripting IPMASQADM PORTFW rules

  ˇ  Updated a few of the Linux Documentation Project (LDP) URLs

  ˇ  Added Quake III support in the module loading sections of all the
     rc.firewall rulesets.

  ˇ  Fixed the IPMASQADM forwards for ICQ


  ˇ  1.72 - 4/14/99 - Dranch:  Added a large list of Windows NAT/Proxy
     alternatives with rough pricing and URLs to the FAQ.


  ˇ  1.71 - 4/13/99 - Dranch:  Added IPCHAINS setups for multiple
     internal MASQed networks.  Changed the ICQ setup to use ICQ's
     default 60 second timeout and change IPFWADM/IPCHAINS timeout to
     160 seconds.  Updated the MASQ and MASQ-DEV email list and archive
     subscription instructions.


  ˇ  1.70 - 3/30/99 - Dranch: Added two new FAQ sections that cover
     SMTP/POP-3 timeout problems and how to masquerade multiple internal
     networks out different external IP addresses with IPROUTE2.


  ˇ  1.65 - 3/29/99 - Dranch: Typo fixes, clarifications of required
     2.2.x kernel options, added dynamic PPP IP address support to the
     strong firewall section, additional quake II module ports, noted
     that the LooseUDP patch is built into later 2.2.x kernels and its
     from Glenn Lamb and not Dan Kegel, added more game info in the
     compatibility section.


  ˇ  1.62 - Dranch:  Make the final first-draft changes to the doc and
     now announce it the the MASQ email list.


  ˇ  1.61 - Dranch:  Make editorial changes, cleaned things up and fixed
     some errors in the Windows95 and NT setups.


  ˇ  1.58 - Dranch:  Addition of the port forwarding sections; LooseUDP
     setup; Ident servers for IRC users, how to read firewall logs,
     deleted the CuSeeme Mini-HOWTO since it is rarely used.


  ˇ  1.55 - Dranch: Complete overhaul, feature and FAQ addition, and
     editing sweep of the v1.50 HOWTO.  Completed the 2.2.x kernel and
     IPCHAINS configurations.  Did a conversion from IPAUTOFW to
     IPPORTFW for the examples that applied.  Added many URLs to various
     other documentation and utility sites.  There are so many changes..
     I hope everyone likes it.  Final publishing of this new rev of the
     HOWTO to the LDP project won't happen until the doc is looked over
     and approved by the IP MASQ email list (then v2.00).


  ˇ  1.50 - Ambrose: A serious update to the HOWTO and the initial
     addition of the 2.2.0 and IPCHAINS configurations.


  ˇ  1.20 - Ambrose: One of the more recent HOWTO versions that solely
     dealt with < 2.0.x kernels and IPFWADM.



