  DNS HOWTO
  Nicolai Langfeldt janl@math.uio.no
  v2.2, 11 February 1999

  HOWTO become a totally small time DNS admin.
  ______________________________________________________________________

  Table of Contents


  1. Preamble

     1.1 Legal stuff
     1.2 Credits and request for help.
     1.3 Dedication

  2. Introduction.

  3. A caching only name server.

     3.1 Starting named
     3.2 Making it even better
     3.3 Congratulations

  4. A

     4.1 But first some dry theory
     4.2 Our own domain
     4.3 The reverse zone
     4.4 Words of caution
     4.5 Why reverse lookups don't work.
        4.5.1 The reverse zone isn't delegated.
        4.5.2 You've got a classless subnet

  5. A real domain example

     5.1 /etc/named.conf (or /var/named/named.conf)
     5.2 /var/named/root.hints
     5.3 /var/named/zone/127.0.0
     5.4 /var/named/zone/land-5.com
     5.5 /var/named/zone/206.6.177

  6. Maintenance

  7. Converting from version 4 to version 8

  8. Questions and Answers

  9. How to become a bigger time DNS admin.



  ______________________________________________________________________

  1.  Preamble

  Keywords: DNS, bind, bind-4, bind-8, named, dialup, ppp, slip, isdn,
  Internet, domain, name, hosts, resolving, caching.


  This document is part of the Linux Documentation Project.



  1.1.  Legal stuff

  (C)opyright 1995-1999 Nicolai Langfeldt. Do not modify without
  amending copyright, distribute freely but retain copyright message.


  1.2.  Credits and request for help.

  I want to thank Arnt Gulbrandsen whom I cause to suffer through the
  drafts to this work and whom provided many useful suggestions.  I also
  want to thank the numerous people that have e-mailed suggestions and
  notes.


  This will never be a finished document, please send me mail about your
  problems and successes, it can make this a better HOWTO.  So please
  send comments and/or questions or money to janl@math.uio.no.  If you
  send e-mail and want an answer please show the simple courtesy of
  making sure that the return address is correct and working.  Also,
  please read the ``QnA'' section before mailing me.  Another thing, I
  can only understand Norwegian and English.



  If you want to translate this HOWTO please notify me so I can keep
  track of what languages it has been published in, and also I can
  notify you when the HOWTO has been updated.


  1.3.  Dedication

  This HOWTO is dedicated to Anne Line Norheim Langfeldt.  Though she
  will probably never read it since she's not that kind of girl.


  2.  Introduction.

  What this is and isn't.


  DNS is is the Domain Name System.  DNS converts machine names to the
  IP addresses that all machines on the net have.  It maps from name to
  address and from address to name, and some other things.  This HOWTO
  documents how to define such mappings using a Linux system.  A mapping
  is simply a association between two things, in this case a machine
  name, like ftp.linux.org, and the machines IP number (or address)
  199.249.150.4.


  DNS is, to the uninitiated (you ;-), one of the more opaque areas of
  network administration.  This HOWTO will try to make a few things
  clearer.  It describes how to set up a simple DNS name server.
  Starting with a caching only server and going on to setting up a
  primary DNS server for a domain.  For more complex setups you can
  check the ``QnA'' section of this document.  If it's not described
  there you will need to read the Real Documentation.  I'll get back to
  what this Real Documentation consists of in ``the last chapter''.


  Before you start on this you should configure your machine so that you
  can telnet in and out of it, and successfully make all kinds of
  connections to the net, and you should especially be able to do telnet
  127.0.0.1 and get your own machine (test it now!).  You also need a
  good /etc/nsswitch.conf (or /etc/host.conf), /etc/resolv.conf and
  /etc/hosts files as a starting point, since I will not explain their
  function here.  If you don't already have all this set up and working
  the NET-3-HOWTO and/or the PPP-HOWTO explains how to set it up.  Read
  them.


  When I say `your machine' I mean the machine you are trying to set up
  DNS on.  Not any other machine you might have that's involved in your
  networking effort.


  I assume you're not behind any kind of firewall that blocks name
  queries.  If you are you will need a special configuration, see the
  section on ``QnA''.


  Name serving on Unix is done by a program called named.  This is a
  part of the ``bind'' package which is coordinated by Paul Vixie for
  The Internet Software Consortium.  Named is included in most Linux
  distributions and is usually installed as /usr/sbin/named.  If you
  have a named you can probably use it; if you don't have one you can
  get a binary off a Linux ftp site, or get the latest and greatest
  source from ftp.isc.org:/isc/bind/src/cur/bind-8/.  This HOWTO is
  about bind version 8.  The old version of the HOWTO, about bind 4 is
  still available at http://www.math.uio.no/~janl/DNS/ in case you use
  bind 4.  If the named man page talks about (at the very end, the FILES
  section) named.conf you have bind 8, if it talks about named.boot you
  have bind 4.  If you have 4 and are security conscious you really
  ought to upgrade to a recent 8.


  DNS is a net-wide database.  Take care about what you put into it.  If
  you put junk into it, you, and others will get junk out of it.  Keep
  your DNS tidy and consistent and you will get good service from it.
  Learn to use it, admin it, debug it and you will be another good admin
  keeping the net from falling to it's knees by mismanagement.


  In this document I state flatly a couple of things that are not
  completely true (they are at least half truths though).  All in the
  interest of simplification.  Things will (probably ;-) work if you
  believe what I say.


  Tip: Make backup copies of all the files I instruct you to change if
  you already have them, so if after going through this nothing works
  you can get it back to your old, working state.


  3.  A caching only name server.

  A first stab at DNS config, very useful for dialup users.


  A caching only name server will find the answer to name queries and
  remember the answer the next time you need it.  This will shorten the
  waiting time the next time significantly, especially if you're on a
  slow connection.


  First you need a file called /etc/named.conf.  This is read when named
  starts.  For now it should simply contain:



  ______________________________________________________________________
  // Config file for caching only name server

  options {
          directory "/var/named";

          // Uncommenting this might help if you have to go through a
          // firewall and things are not working out:

          // query-source port 53;
  };

  zone "." {
          type hint;
          file "root.hints";
  };

  zone "0.0.127.in-addr.arpa" {
          type master;
          file "pz/127.0.0";
  };
  ______________________________________________________________________



  The `directory' line tells named where to look for files.  All files
  named subsequently will be relative to this.  Thus pz is a directory
  under /var/named, i.e., /var/named/pz.  /var/named is the right
  directory according to the Linux File system Standard.


  The file named /var/named/root.hints is named in this.
  /var/named/root.hints should contain this:



  ______________________________________________________________________
  ;
  ; There might be opening comments here if you already have this file.
  ; If not don't worry.
  ;
  .                     6D IN NS        G.ROOT-SERVERS.NET.
  .                     6D IN NS        J.ROOT-SERVERS.NET.
  .                     6D IN NS        K.ROOT-SERVERS.NET.
  .                     6D IN NS        L.ROOT-SERVERS.NET.
  .                     6D IN NS        M.ROOT-SERVERS.NET.
  .                     6D IN NS        A.ROOT-SERVERS.NET.
  .                     6D IN NS        H.ROOT-SERVERS.NET.
  .                     6D IN NS        B.ROOT-SERVERS.NET.
  .                     6D IN NS        C.ROOT-SERVERS.NET.
  .                     6D IN NS        D.ROOT-SERVERS.NET.
  .                     6D IN NS        E.ROOT-SERVERS.NET.
  .                     6D IN NS        I.ROOT-SERVERS.NET.
  .                     6D IN NS        F.ROOT-SERVERS.NET.

  G.ROOT-SERVERS.NET.     5w6d16h IN A    192.112.36.4
  J.ROOT-SERVERS.NET.     5w6d16h IN A    198.41.0.10
  K.ROOT-SERVERS.NET.     5w6d16h IN A    193.0.14.129
  L.ROOT-SERVERS.NET.     5w6d16h IN A    198.32.64.12
  M.ROOT-SERVERS.NET.     5w6d16h IN A    202.12.27.33
  A.ROOT-SERVERS.NET.     5w6d16h IN A    198.41.0.4
  H.ROOT-SERVERS.NET.     5w6d16h IN A    128.63.2.53
  B.ROOT-SERVERS.NET.     5w6d16h IN A    128.9.0.107
  C.ROOT-SERVERS.NET.     5w6d16h IN A    192.33.4.12
  D.ROOT-SERVERS.NET.     5w6d16h IN A    128.8.10.90
  E.ROOT-SERVERS.NET.     5w6d16h IN A    192.203.230.10
  I.ROOT-SERVERS.NET.     5w6d16h IN A    192.36.148.17
  F.ROOT-SERVERS.NET.     5w6d16h IN A    192.5.5.241
  ______________________________________________________________________



  The file describes the root name servers in the world.  This changes
  over time and must be maintained.  See the ``maintenance section'' for
  how to keep it up to date.


  The next section in named.conf is the last zone. I will explain its
  use in a later chapter, for now just make this a file named 127.0.0 in
  the subdirectory pz:


  ______________________________________________________________________
  @               IN      SOA     ns.linux.bogus. hostmaster.linux.bogus. (
                                  1       ; Serial
                                  8H      ; Refresh
                                  2H      ; Retry
                                  1W      ; Expire
                                  1D)     ; Minimum TTL
                          NS      ns.linux.bogus.
  1                       PTR     localhost.
  ______________________________________________________________________



  Next, you need a /etc/resolv.conf looking something like this:



  ______________________________________________________________________
  search subdomain.your-domain.edu your-domain.edu
  nameserver 127.0.0.1
  ______________________________________________________________________



  The `search' line specifies what domains should be searched for any
  host names you want to connect to.  The `nameserver' line specifies
  the address of your nameserver, in this case your own machine since
  that is where your named runs (127.0.0.1 is right, no matter if your
  machine has an other address too).  If you want to list several name
  servers put in one `nameserver' line for each. (Note: Named never
  reads this file, the resolver that uses named does.)


  To illustrate what this file does: If a client tries to look up foo,
  then foo.subdomain.your-domain.edu is tried first, then foo.your-
  fomain.edu, finally foo.  If a client tries to look up
  sunsite.unc.edu, sunsite.unc.edu.subdomain.your-domain.edu is tried
  first (yes, it's silly, but that's the way it works), then
  sunsite.unc.edu.your-domain.edu, and finally sunsite.unc.edu.  You may
  not want to put in too many domains in the search line, it takes time
  to search them all.


  The example assumes you belong in the domain subdomain.your-
  domain.edu, your machine then, is probably called your-
  machine.subdomain.your-domain.edu.  The search line should not contain
  your TLD (Top Level Domain, `edu' in this case).  If you frequently
  need to connect to hosts in another domain you can add that domain to
  the search line like this:


  ______________________________________________________________________
  search subdomain.your-domain.edu your-domain.edu other-domain.com
  ______________________________________________________________________



  and so on. Obviously you need to put real domain names in instead.
  Please note the lack of periods at the end of the domain names.  This
  is important, please note the lack of periods at the end of the domain
  names.


  Next, depending on your libc version you either need to fix
  /etc/nsswitch.conf or /etc/host.conf.  If you already have
  nsswitch.conf that's what we'll fix, if not, we'll fix host.conf.


  /etc/nsswitch.conf


  This is a long file specifying where to get different kinds of data
  types, from what file or database.  It usually contains helpful
  comments at the top, which you should consider reading.  After that
  find the line starting with `hosts:', it should read


  ______________________________________________________________________
  hosts:      files dns
  ______________________________________________________________________


  If there is no line starting with `hosts:' then put in the one above.
  It says that programs should first look in the /etc/hosts file, then
  check DNS according to resolv.conf.


  /etc/host.conf


  It probably contains several lines, one should start with order and it
  should look like this:


  ______________________________________________________________________
  order hosts,bind
  ______________________________________________________________________



  If there is no `order' line you should add one.  It tells the host
  name resolving routines to first look in /etc/hosts, then ask the name
  server (which you in resolv.conf said is at 127.0.0.1).


  3.1.  Starting named

  After all this it's time to start named.  If you're using a dialup
  connection connect first.  Type `ndc start', and press return, no
  options.  If that does not work try `/usr/sbin/ndc start' instead.  If
  that back-fires see the ``QnA'' section.  If you view your syslog
  message file (usually called /var/adm/messages, but another directory
  to look in is /var/log and another file to look in is syslog) while
  starting named (do tail -f /var/log/messages) you should see something
  like:


  (the lines ending in \ continue on the next line)



       Feb 15 01:26:17 roke named[6091]: starting.  named 8.1.1 Sat Feb 14 \
         00:18:20 MET 1998 ^Ijanl@roke.uio.no:/var/tmp/bind-8.1.1/src/bin/named
       Feb 15 01:26:17 roke named[6091]: cache zone "" (IN) loaded (serial 0)
       Feb 15 01:26:17 roke named[6091]: master zone "0.0.127.in-addr.arpa" \
         (IN) loaded (serial 1)
       Feb 15 01:26:17 roke named[6091]: listening [127.0.0.1].53 (lo)
       Feb 15 01:26:17 roke named[6091]: listening [129.240.230.92].53 (ippp0)
       Feb 15 01:26:17 roke named[6091]: Forwarding source address is [0.0.0.0].1040
       Feb 15 01:26:17 roke named[6092]: Ready to answer queries.



  If there are any messages about errors then there is a mistake.  Named
  will name the file it is in (one of named.conf and root.hints I hope
  :-) Kill named and go back and check the file.


  Now you can test your setup.  Start nslookup to examine your work.



  $ nslookup
  Default Server:  localhost
  Address:  127.0.0.1

  >



  If that's what you get it's working.  We hope.  Anything else, go back
  and check everything.  Each time you change the named.conf file you
  need to restart named using the ndc restart command.


  Now you can enter a query.  Try looking up some machine close to you.
  pat.uio.no is close to me, at the University of Oslo:



       > pat.uio.no
       Server:  localhost
       Address:  127.0.0.1

       Name:    pat.uio.no
       Address:  129.240.130.16



  nslookup now asked your named to look for the machine pat.uio.no.  It
  then contacted one of the name server machines named in your
  root.hints file, and asked its way from there.  It might take tiny
  while before you get the result as it may need to search all the
  domains you named in /etc/resolv.conf.


  If you ask the same again you get this:



       > pat.uio.no
       Server:  localhost
       Address:  127.0.0.1

       Non-authoritative answer:
       Name:    pat.uio.no
       Address:  129.240.2.50



  Note the ``Non-authoritative answer:'' line we got this time around.
  That means that named did not go out on the network to ask this time,
  the information is in the cache now.  But the cached information might
  be out of date (stale).  So you are informed of this (very slight)
  possibility by it saying `Non-authorative answer:'.  When nslookup
  says this the second time you ask for a host it's a sure sign that
  named caches the information and that it's working.  You exit nslookup
  by giving the command `exit'.



  3.2.  Making it even better

  In large, well organized, academic or ISP (Internet Service Provider)
  networks you will sometimes find that the network people has set up a
  forwarder hierarchy of DNS servers which helps lighten the internal
  network load and on the outside servers as well.  It's not easy to
  know if you're inside such a network or not.  It is however not
  important and by using the DNS server of your network provider as a
  ``forwarder'' you can make the responses to queries faster and less of
  a load on your network.  If you use a modem this can be quite a win.
  For the sake of this example we assume that your network provider has
  two name servers they want you to use, with IP numbers 10.0.0.1 and
  10.1.0.1.  Then, in your named.conf file, inside the opening section
  called ``options'' insert these lines:


  ______________________________________________________________________
             forward first;
             forwarders {
                  10.0.0.1;
                  10.1.0.1;
              };
  ______________________________________________________________________



  Restart your nameserver and test it with nslookup.  Should work fine.


  3.3.  Congratulations

  Now you know how to set up a caching named.  Take a beer, milk, or
  whatever you prefer to celebrate it.


  4.  A simple  domain.

  How to set up your own domain.


  4.1.  But first some dry theory

  Before we really start this section I'm going to serve you some theory
  on and an example of how DNS works.  And you're going to read it
  because it's good for you.  If you don't want to you should at least
  skim it very quickly.  Stop skimming when you get to what should go in
  your named.conf file.


  DNS is a hierarchical, tree structured, system.  The top is written
  `.' and pronounced `root'.  Under . there are a number of Top Level
  Domains (TLDs), the best known ones are ORG, COM, EDU and NET, but
  there are many more.  Just like a tree it has a root and it branches
  out.  If you have any computer science background you will recognize
  DNS as a search tree, and you will be able to find nodes, leaf nodes
  and edges.


  When looking for a machine the query proceeds recursively into the
  hierarchy starting at the top.  If you want to find out the address of
  prep.ai.mit.edu your name server has to find a name server that serves
  edu.  It asks a . server (it already knows the .  servers, that's what
  the root.hints file is for), the .  server gives a list of edu
  servers:

       $ nslookup
       Default Server:  localhost
       Address:  127.0.0.1



  Start asking a root server:



       > server c.root-servers.net.
       Default Server:  c.root-servers.net
       Address:  192.33.4.12



  Set the Query type to NS (name server records):



       > set q=ns



  Ask about edu:



       > edu.



  The trailing . here is significant, it tells nslookup we're asking
  that edu is right under . (and not under any of our search domains, it
  speeds the search).



       edu     nameserver = A.ROOT-SERVERS.NET
       edu     nameserver = H.ROOT-SERVERS.NET
       edu     nameserver = B.ROOT-SERVERS.NET
       edu     nameserver = C.ROOT-SERVERS.NET
       edu     nameserver = D.ROOT-SERVERS.NET
       edu     nameserver = E.ROOT-SERVERS.NET
       edu     nameserver = I.ROOT-SERVERS.NET
       edu     nameserver = F.ROOT-SERVERS.NET
       edu     nameserver = G.ROOT-SERVERS.NET
       A.ROOT-SERVERS.NET      internet address = 198.41.0.4
       H.ROOT-SERVERS.NET      internet address = 128.63.2.53
       B.ROOT-SERVERS.NET      internet address = 128.9.0.107
       C.ROOT-SERVERS.NET      internet address = 192.33.4.12
       D.ROOT-SERVERS.NET      internet address = 128.8.10.90
       E.ROOT-SERVERS.NET      internet address = 192.203.230.10
       I.ROOT-SERVERS.NET      internet address = 192.36.148.17
       F.ROOT-SERVERS.NET      internet address = 192.5.5.241
       G.ROOT-SERVERS.NET      internet address = 192.112.36.4



  This tells us that all ROOT-SERVERS.NET servers serves EDU., so we can
  go on asking any of them.  We'll continue asking C.  Now we want to
  know who serves the next level of the domain name: mit.edu.:



       > mit.edu.
       Server:  c.root-servers.net
       Address:  192.33.4.12

       Non-authoritative answer:
       mit.edu nameserver = W20NS.mit.edu
       mit.edu nameserver = BITSY.mit.edu
       mit.edu nameserver = STRAWB.mit.edu

       Authoritative answers can be found from:
       W20NS.mit.edu   internet address = 18.70.0.160
       BITSY.mit.edu   internet address = 18.72.0.3
       STRAWB.mit.edu  internet address = 18.71.0.151



  steawb, w20ns and bitsy all serves mit.edu, we select one and inquire
  about the name one more level up: ai.mit.edu:



       > server W20NS.mit.edu.



  Host names are not case sensitive, but I use my mouse to cut and paste
  so it gets copied as-is from the screen.



  Server:  W20NS.mit.edu
  Address:  18.70.0.160

  > ai.mit.edu.
  Server:  W20NS.mit.edu
  Address:  18.70.0.160

  Non-authoritative answer:
  ai.mit.edu      nameserver = ALPHA-BITS.AI.MIT.EDU
  ai.mit.edu      nameserver = GRAPE-NUTS.AI.MIT.EDU
  ai.mit.edu      nameserver = TRIX.AI.MIT.EDU
  ai.mit.edu      nameserver = MUESLI.AI.MIT.EDU
  ai.mit.edu      nameserver = LIFE.AI.MIT.EDU
  ai.mit.edu      nameserver = BEET-CHEX.AI.MIT.EDU
  ai.mit.edu      nameserver = MINI-WHEATS.AI.MIT.EDU
  ai.mit.edu      nameserver = COUNT-CHOCULA.AI.MIT.EDU
  ai.mit.edu      nameserver = MINTAKA.LCS.MIT.EDU

  Authoritative answers can be found from:
  AI.MIT.EDU      nameserver = ALPHA-BITS.AI.MIT.EDU
  AI.MIT.EDU      nameserver = GRAPE-NUTS.AI.MIT.EDU
  AI.MIT.EDU      nameserver = TRIX.AI.MIT.EDU
  AI.MIT.EDU      nameserver = MUESLI.AI.MIT.EDU
  AI.MIT.EDU      nameserver = LIFE.AI.MIT.EDU
  AI.MIT.EDU      nameserver = BEET-CHEX.AI.MIT.EDU
  AI.MIT.EDU      nameserver = MINI-WHEATS.AI.MIT.EDU
  AI.MIT.EDU      nameserver = COUNT-CHOCULA.AI.MIT.EDU
  AI.MIT.EDU      nameserver = MINTAKA.LCS.MIT.EDU
  ALPHA-BITS.AI.MIT.EDU   internet address = 128.52.32.5
  GRAPE-NUTS.AI.MIT.EDU   internet address = 128.52.36.4
  TRIX.AI.MIT.EDU internet address = 128.52.37.6
  MUESLI.AI.MIT.EDU       internet address = 128.52.39.7
  LIFE.AI.MIT.EDU internet address = 128.52.32.80
  BEET-CHEX.AI.MIT.EDU    internet address = 128.52.32.22
  MINI-WHEATS.AI.MIT.EDU  internet address = 128.52.54.11
  COUNT-CHOCULA.AI.MIT.EDU        internet address = 128.52.38.22
  MINTAKA.LCS.MIT.EDU     internet address = 18.26.0.36



  So museli.ai.mit.edu is a nameserver for ai.mit.edu:



       > server MUESLI.AI.MIT.EDU
       Default Server:  MUESLI.AI.MIT.EDU
       Address:  128.52.39.7



  Now I change query type, we've found the name server so now we're
  going to ask about everything wheaties knows about prep.ai.mit.edu.



  > set q=any
  > prep.ai.mit.edu.
  Server:  MUESLI.AI.MIT.EDU
  Address:  128.52.39.7

  prep.ai.mit.edu CPU = dec/decstation-5000.25    OS = unix
  prep.ai.mit.edu
          inet address = 18.159.0.42, protocol = tcp
            ftp  telnet  smtp  finger
  prep.ai.mit.edu preference = 1, mail exchanger = gnu-life.ai.mit.edu
  prep.ai.mit.edu internet address = 18.159.0.42
  ai.mit.edu      nameserver = beet-chex.ai.mit.edu
  ai.mit.edu      nameserver = alpha-bits.ai.mit.edu
  ai.mit.edu      nameserver = mini-wheats.ai.mit.edu
  ai.mit.edu      nameserver = trix.ai.mit.edu
  ai.mit.edu      nameserver = muesli.ai.mit.edu
  ai.mit.edu      nameserver = count-chocula.ai.mit.edu
  ai.mit.edu      nameserver = mintaka.lcs.mit.edu
  ai.mit.edu      nameserver = life.ai.mit.edu
  gnu-life.ai.mit.edu     internet address = 128.52.32.60
  beet-chex.ai.mit.edu    internet address = 128.52.32.22
  alpha-bits.ai.mit.edu   internet address = 128.52.32.5
  mini-wheats.ai.mit.edu  internet address = 128.52.54.11
  trix.ai.mit.edu internet address = 128.52.37.6
  muesli.ai.mit.edu       internet address = 128.52.39.7
  count-chocula.ai.mit.edu        internet address = 128.52.38.22
  mintaka.lcs.mit.edu     internet address = 18.26.0.36
  life.ai.mit.edu internet address = 128.52.32.80



  So starting at . we found the successive name servers for the each
  level in the domain name.  If you had used your own DNS server instead
  of using all those other servers, your named would of-course cache all
  the information it found while digging this out for you, and it would
  not have to ask again for a while.


  In the tree analogue each ``.'' in the name is a branching point.  And
  each part between the ``.''s are the names of individual branches in
  the tree.


  We climb the tree by taking the name we want (prep.ai.mit.edu) first
  finding the root (.) and then looking for the next branch to climb, in
  this case edu.  Once we have found it we climb it by switching to the
  server that knows about that part of the name.  Next we look for the
  mit branch over the edu branch (the combined name is mit.edu) and
  climb it by switching to a server that knows about mit.edu.  Again we
  look for the next branch, it's ai.mit.edu and again we switch to the
  server that knows about it.  Now we have arrived at the right server,
  at the right branching point.  The last part is finding
  prep.ai.mit.edu, which is simple.  In computer science we usually call
  prep a leaf on the tree.


  A much less talked about, but just as important domain is in-
  addr.arpa.  It too is nested like the `normal' domains.  in-addr.arpa
  allows us to get the hosts name when we have its address.  A important
  thing here is to note that ip addresses are written in reverse order
  in the in-addr.arpa domain.  If you have the address of a machine:
  192.128.52.43 named proceeds just like for the prep.ai.mit.edu
  example: find arpa. servers.  Find in-addr.arpa. servers, find 192.in-
  addr.arpa. servers, find 128.192.in-addr.arpa. servers, find
  52.128.192.in-addr.arpa.  servers.  Find needed records for
  43.52.128.192.in-addr.arpa.  Clever huh? (Say `yes'.)  The reversion
  of the numbers can be confusing for years though.


  I have just told a lie.  DNS does not work precisely the way I just
  told you.  But it's close enough.


  4.2.  Our own domain

  Now to define our own domain.  We're going to make the domain
  linux.bogus and define machines in it.  I use a totally bogus domain
  name to make sure we disturb no-one Out There.


  One more thing before we start: Not all characters are allowed in host
  names.  We're restricted to the characters of the English alphabet: a-
  z, and numbers: 0-9 and the character '-' (dash).  Keep to those
  characters.  Upper and lower-case characters are the same for DNS, so
  pat.uio.no is identical to Pat.UiO.No.


  We've already started this part with this line in named.conf:


  ______________________________________________________________________
  zone "0.0.127.in-addr.arpa" {
          type master;
          file "pz/127.0.0";
  };
  ______________________________________________________________________



  Please note the lack of `.' at the end of the domain names in this
  file.  This says that now we will define the zone 0.0.127.in-
  addr.arpa, that we're the master server for it and that it is stored
  in a file called pz/127.0.0.  We've already set up this file, it
  reads:


  ______________________________________________________________________
  @               IN      SOA     ns.linux.bogus. hostmaster.linux.bogus. (
                                  1       ; Serial
                                  8H      ; Refresh
                                  2H      ; Retry
                                  1W      ; Expire
                                  1D)     ; Minimum TTL
                          NS      ns.linux.bogus.
  1                       PTR     localhost.
  ______________________________________________________________________



  Please note the `.' at the end of all the full domain names in this
  file, in contrast to the named.conf file above. Some people like to
  start each zone file with a $ORIGIN directive, but this is
  superfluous.  The origin (where in the DNS hierarchy it belongs) of a
  zone file is specified in the zone section of the named.conf file, in
  this case it's 0.0.127.in-addr.arpa.



  This `zone file' contains 3 `resource records' (RRs): A SOA RR.  A NS
  RR and a PTR RR.  SOA is short for Start Of Authority.  The `@' is a
  special notation meaning the origin, and since the `domain' column for
  this file says 0.0.127.in-addr.arpa the first line really means



       0.0.127.in-addr.arpa.   IN      SOA ...



  NS is the Name Server RR.  There is no '@' at the start of this line,
  it is implicit since the last line started with a '@'.  Saves some
  typing that.  So the NS line could also be written



       0.0.127.in-addr.arpa.   IN      NS      ns.linux.bogus



  It tells DNS what machine is the name server of the domain 0.0.127.in-
  addr.arpa, it is ns.linux.bogus.  'ns' is a customary name for name-
  servers, but as with web servers who are customarily named
  www.something the name may be anything.

  And finally the PTR record says that the host at address 1 in the
  subnet 0.0.127.in-addr.arpa, i.e., 127.0.0.1 is named localhost.


  The SOA record is the preamble to all zone files, and there should be
  exactly one in each zone file.  It describes the zone, where it comes
  from (a machine called ns.linux.bogus), who is responsible for its
  contents (hostmaster@linux.bogus, you should insert your e-mail
  address here), what version of the zone file this is (serial: 1), and
  other things having to do with caching and secondary DNS servers.  For
  the rest of the fields (refresh, retry, expire and minimum) use the
  numbers used in this HOWTO and you should be safe.


  Now restart your named (the command is ndc restart) and use nslookup
  to examine what you've done:



       $ nslookup

       Default Server:  localhost
       Address:  127.0.0.1

       > 127.0.0.1
       Server:  localhost
       Address:  127.0.0.1

       Name:    localhost
       Address:  127.0.0.1



  so it manages to get localhost from 127.0.0.1, good.  Now for our main
  task, the linux.bogus domain, insert a new 'zone' section in
  named.conf:


  ______________________________________________________________________
  zone "linux.bogus" {
          notify no;
          type master;
          file "pz/linux.bogus";
  };
  ______________________________________________________________________



  Note again the lack of ending `.' on the domain name in the named.conf
  file.


  In the linux.bogus zone file we'll put some totally bogus data:


  ______________________________________________________________________
  ;
  ; Zone file for linux.bogus
  ;
  ; The full zone file
  ;
  @       IN      SOA     ns.linux.bogus. hostmaster.linux.bogus. (
                          199802151       ; serial, todays date + todays serial #
                          8H              ; refresh, seconds
                          2H              ; retry, seconds
                          1W              ; expire, seconds
                          1D )            ; minimum, seconds
  ;
                  NS      ns              ; Inet Address of name server
                  MX      10 mail.linux.bogus     ; Primary Mail Exchanger
                  MX      20 mail.friend.bogus.   ; Secondary Mail Exchanger
  ;
  localhost       A       127.0.0.1
  ns              A       192.168.196.2
  mail            A       192.168.196.4
  ______________________________________________________________________



  Two things must be noted about the SOA record.  ns.linux.bogus must be
  a actual machine with a A record.  It is not legal to have a CNAME
  record for he machine mentioned in the SOA record.  It's name need not
  be `ns', it could be any legal host name.  Next,
  hostmaster.linux.bogus should be read as hostmaster@linux.bogus, this
  should be a mail alias, or a mailbox, where the person(s) maintaining
  DNS should read mail frequently.  Any mail regarding the domain will
  be sent to the address listed here.  The name need not be
  `hostmaster', it can be your normal e-mail address, but the e-mail
  address `hostmaster' is often expected to work as well.


  There is one new RR type in this file, the MX, or Mail eXchanger RR.
  It tells mail systems where to send mail that is addressed to
  someone@linux.bogus, namely too mail.linux.bogus or mail.friend.bogus.
  The number before each machine name is that MX RRs priority.  The RR
  with the lowest number (10) is the one mail should be sent to if
  possible.  If that fails the mail can be sent to one with a higher
  number, a secondary mail handler, i.e., mail.friend.bogus which has
  priority 20 here.
  Restart named by running ndc restart.  Examine the results with
  nslookup:



       $ nslookup
       > set q=any
       > linux.bogus
       Server:  localhost
       Address:  127.0.0.1

       linux.bogus
               origin = ns.linux.bogus
               mail addr = hostmaster.linux.bogus
               serial = 199802151
               refresh = 28800 (8 hours)
               retry   = 7200 (2 hours)
               expire  = 604800 (7 days)
               minimum ttl = 86400 (1 day)
       linux.bogus     nameserver = ns.linux.bogus
       linux.bogus     preference = 10, mail exchanger = mail.linux.bogus.linux.bogus
       linux.bogus     preference = 20, mail exchanger = mail.friend.bogus
       linux.bogus     nameserver = ns.linux.bogus
       ns.linux.bogus  internet address = 192.168.196.2
       mail.linux.bogus        internet address = 192.168.196.4



  Upon careful examination you will discover a bug.  The line



       linux.bogus     preference = 10, mail exchanger = mail.linux.bogus.linux.bogus



  is all wrong.  It should be



       linux.bogus     preference = 10, mail exchanger = mail.linux.bogus



  I deliberately made a mistake so you could learn from it :-) Looking
  in the zone file we find that the line



                       MX      10 mail.linux.bogus     ; Primary Mail Exchanger



  is missing a period.  Or has a 'linux.bogus' too many.  If a machine
  name does not end in a period in a zone file the origin is added to
  its end causing the double linux.bogus.linux.bogus.  So either



  ______________________________________________________________________
                  MX      10 mail.linux.bogus.    ; Primary Mail Exchanger
  ______________________________________________________________________



  or


  ______________________________________________________________________
                  MX      10 mail                 ; Primary Mail Exchanger
  ______________________________________________________________________



  is correct.  I prefer the latter form, it's less to type.  There are
  some bind experts that disagree, and some that agree with this.  In a
  zone file the domain should either be written out and ended with a `.'
  or it should not be included at all, in which case it defaults to the
  origin.


  I must stress that in the named.conf file there should not be `.'s
  after the domain names.  You have no idea how many times a `.' too
  many or few have fouled up things and confused the h*ll out of people.


  So having made my point here is the new zone file, with some extra
  information in it as well:



  ______________________________________________________________________
  ;
  ; Zone file for linux.bogus
  ;
  ; The full zone file
  ;
  @       IN      SOA     ns.linux.bogus. hostmaster.linux.bogus. (
                          199802151       ; serial, todays date + todays serial #
                          8H              ; refresh, seconds
                          2H              ; retry, seconds
                          1W              ; expire, seconds
                          1D )            ; minimum, seconds
  ;
                  TXT     "Linux.Bogus, your DNS consultants"
                  NS      ns              ; Inet Address of name server
                  NS      ns.friend.bogus.
                  MX      10 mail         ; Primary Mail Exchanger
                  MX      20 mail.friend.bogus. ; Secondary Mail Exchanger

  localhost       A       127.0.0.1

  gw              A       192.168.196.1
                  HINFO   "Cisco" "IOS"
                  TXT     "The router"

  ns              A       192.168.196.2
                  MX      10 mail
                  MX      20 mail.friend.bogus.
                  HINFO   "Pentium" "Linux 2.0"
  www             CNAME   ns

  donald          A       192.168.196.3
                  MX      10 mail
                  MX      20 mail.friend.bogus.
                  HINFO   "i486"      "Linux 2.0"
                  TXT     "DEK"

  mail            A       192.168.196.4
                  MX      10 mail
                  MX      20 mail.friend.bogus.
                  HINFO   "386sx" "Linux 1.2"

  ftp             A       192.168.196.5
                  MX      10 mail
                  MX      20 mail.friend.bogus.
                  HINFO   "P6" "Linux 2.1.86"
  ______________________________________________________________________



  There are a number of new RRs here: HINFO (Host INFOrmation) has two
  parts, it's a good habit to quote each.  The first part is the
  hardware or CPU on the machine, and the second part the software or OS
  on the machine.  The machine called 'ns' has a Pentium CPU and runs
  Linux 2.0.  CNAME (Canonical NAME) is a way to give each machine
  several names.  So www is an alias for ns.


  CNAME record usage is a bit controversial.  But it's safe to follow
  the rule that a MX, CNAME or SOA record should never refer to a CNAME
  record, they should only refer to something with a A record, so it is
  inadvisable to have



  ______________________________________________________________________
  foobar          CNAME   www                     ; NO!
  ______________________________________________________________________



  but correct to have


  ______________________________________________________________________
  foobar          CNAME   ns                      ; Yes!
  ______________________________________________________________________



  It's also safe to assume that a CNAME is not a legal host name for a
  e-mail address: webmaster@www.linux.bogus is an illegal e-mail address
  given the setup above.  You can expect quite a few mail admins Out
  There to enforce this rule even if it works for you.  The way to avoid
  this is to use A records (and perhaps some others too, like a MX
  record) instead:


  ______________________________________________________________________
  www             A       192.168.196.2
  ______________________________________________________________________



  A number of the arch-bind-wizards, recommend not using CNAME at all.
  But the discussion of why or why not is beyond this HOWTO.


  But as you see, this HOWTO and many sites does not follow this rule.


  Load the new database by running ndc reload, this causes named to read
  its files again.



       $ nslookup
       Default Server:  localhost
       Address:  127.0.0.1

       > ls -d linux.bogus



  This means that all records should be listed.  It results in this:



  [localhost]
  $ORIGIN linux.bogus.
  @                       1D IN SOA       ns hostmaster (
                                          199802151       ; serial
                                          8H              ; refresh
                                          2H              ; retry
                                          1W              ; expiry
                                          1D )            ; minimum

                          1D IN NS        ns
                          1D IN NS        ns.friend.bogus.
                          1D IN TXT       "Linux.Bogus, your DNS consultants"
                          1D IN MX        10 mail
                          1D IN MX        20 mail.friend.bogus.
  gw                      1D IN A         192.168.196.1
                          1D IN HINFO     "Cisco" "IOS"
                          1D IN TXT       "The router"
  mail                    1D IN A         192.168.196.4
                          1D IN MX        10 mail
                          1D IN MX        20 mail.friend.bogus.
                          1D IN HINFO     "386sx" "Linux 1.0.9"
  localhost               1D IN A         127.0.0.1
  www                     1D IN CNAME     ns
  donald                  1D IN A         192.168.196.3
                          1D IN MX        10 mail
                          1D IN MX        20 mail.friend.bogus.
                          1D IN HINFO     "i486" "Linux 1.2"
                          1D IN TXT       "DEK"
  ftp                     1D IN A         192.168.196.5
                          1D IN MX        10 mail
                          1D IN MX        20 mail.friend.bogus.
                          1D IN HINFO     "P6" "Linux 1.3.59"
  ns                      1D IN A         192.168.196.2
                          1D IN MX        10 mail
                          1D IN MX        20 mail.friend.bogus.
                          1D IN HINFO     "Pentium" "Linux 1.2"



  That's good.  As you see it looks a lot like the zone file itself.
  Let's check what it says for www alone:



       > set q=any
       > www.linux.bogus.
       Server:  localhost
       Address:  127.0.0.1

       www.linux.bogus canonical name = ns.linux.bogus
       linux.bogus     nameserver = ns.linux.bogus
       linux.bogus     nameserver = ns.friend.bogus
       ns.linux.bogus  internet address = 192.168.196.2



  In other words, the real name of www.linux.bogus is ns.linux.bogus,
  and it gives you some of the information it has about ns as well,
  enough to connect to it if you were a program.



  Now we're halfway.


  4.3.  The reverse zone

  Now programs can convert the names in linux.bogus to addresses which
  they can connect to.  But also required is a reverse zone, one making
  DNS able to convert from an address to a name.  This name is used buy
  a lot of servers of different kinds (FTP, IRC, WWW and others) to
  decide if they want to talk to you or not, and if so, maybe even how
  much priority you should be given.  For full access to all services on
  the Internet a reverse zone is required.


  Put this in named.conf:


  ______________________________________________________________________
  zone "196.168.192.in-addr.arpa" {
          notify no;
          type master;
          file "pz/192.168.196";
  };
  ______________________________________________________________________



  This is exactly as with the 0.0.127.in-addr.arpa, and the contents are
  similar:


  ______________________________________________________________________
  @       IN      SOA     ns.linux.bogus. hostmaster.linux.bogus. (
                          199802151 ; Serial, todays date + todays serial
                          8H      ; Refresh
                          2H      ; Retry
                          1W      ; Expire
                          1D)     ; Minimum TTL
                  NS      ns.linux.bogus.

  1               PTR     gw.linux.bogus.
  2               PTR     ns.linux.bogus.
  3               PTR     donald.linux.bogus.
  4               PTR     mail.linux.bogus.
  5               PTR     ftp.linux.bogus.
  ______________________________________________________________________



  Now you restart your named (ndc restart) and examine your work with
  nslookup again:


  ______________________________________________________________________
  > 192.168.196.4
  Server:  localhost
  Address:  127.0.0.1

  Name:    mail.linux.bogus
  Address:  192.168.196.4
  ______________________________________________________________________



  so, it looks OK, dump the whole thing to examine that too:


  ______________________________________________________________________
  > ls -d 196.168.192.in-addr.arpa
  [localhost]
  $ORIGIN 196.168.192.in-addr.arpa.
  @                       1D IN SOA       ns.linux.bogus. hostmaster.linux.bogus. (
                                          199802151       ; serial
                                          8H              ; refresh
                                          2H              ; retry
                                          1W              ; expiry
                                          1D )            ; minimum

                          1D IN NS        ns.linux.bogus.
  1                       1D IN PTR       gw.linux.bogus.
  2                       1D IN PTR       ns.linux.bogus.
  3                       1D IN PTR       donald.linux.bogus.
  4                       1D IN PTR       mail.linux.bogus.
  5                       1D IN PTR       ftp.linux.bogus.
  @                       1D IN SOA       ns.linux.bogus. hostmaster.linux.bogus. (
                                          199802151       ; serial
                                          8H              ; refresh
                                          2H              ; retry
                                          1W              ; expiry
                                          1D )            ; minimum
  ______________________________________________________________________



  Looks good!  If your output didn't look like that look for error-
  messages in your syslog, I explained how to do that at the very
  beginning of this chapter.


  4.4.  Words of caution

  There are some things I should add here.  The IP numbers used in the
  examples above are taken from one of the blocks of 'private nets',
  i.e., they are not allowed to be used publicly on the internet.  So
  they are safe to use in an example in a HOWTO.  The second thing is
  the notify no; line.  It tells named not to notify its secondary
  (slave) servers when it has gotten a update to one of its zone files.
  In bind-8 the named can notify the other servers listed in NS records
  in the zone file when a zone is updated.  This is handy for ordinary
  use, but for private experiments with zones this feature should be
  off, we don't want the experiment to pollute the Internet do we?


  And, of course, this domain is highly bogus, and so are all the
  addresses in it.  For a real example of a real-life domain see the
  next main-section.


  4.5.  Why reverse lookups don't work.

  There are a couple of ``gotchas'' that normally are avoided with name
  lookups that are often seen when setting up reverse zones.  Before you
  go on you need reverse lookups of your machines working on your own
  nameserver.  If it isn't go back and fix it before continuing.


  I will discuss two failures of reverse lookups as seen from outside
  your network:

  4.5.1.  The reverse zone isn't delegated.

  When you ask a service provider for a network-address range and a
  domain name the domain name is normally delegated as a matter of
  course.  A delegation is the glue NS record that helps you get from
  one nameserver to another as explained in the dry theory section
  above.  You read that, right?  If your reverse zone dosn't work go
  back and read it.  Now.


  The reverse zone also needs to be delegated.  If you got the
  192.168.196 net with the linux.bogus domain from your provider they
  need to put NS records in for your reverse zone as well as for your
  forward zone.  If you follow the chain from in-addr.arpa and up to
  your net you will probably find a break in the chain.  Most probably
  at your service provider.  Having found the break in the chain contact
  your service-provider and ask them to correct the error.


  4.5.2.  You've got a classless subnet

  This is a somewhat advanced topic, but classless subnets are very
  common these days and you probably have one unless you're a medium
  sized company.


  A classless subnet is what keeps the Internet going these days.  Some
  years ago there was much ado about the shortage of ip numbers.  The
  smart people in IETF (the Internet Engineering Task Force, they keep
  the Internet working) stuck their heads together and solved the
  problem.  At a price.  The price is that you'll get less than a ``C''
  subnet and some things may break.  Please see Ask Mr. DNS at
  http://www.acmebw.com/askmrdns/00007.htm for an good explanation of
  this and how to handle it.


  Did you read it?  I'm not going to explain it so please read it.


  The first part of the problem is that your ISP must understand the
  technique described by Mr. DNS.  Not all small ISPs have a working
  understanding of this.  If so you might have to explain to them and be
  persistent.  But be sure you understand it first ;-).  They will then
  set up a nice reverse zone at their server which you can examine for
  correctness with nslookup.


  The second and last part of the problem is that you must understand
  the technique.  If you're unsure go back and read about it again.
  Then you can set up your own classless reverse zone as described by
  Mr. DNS.


  There is another trap lurking here.  Old resolvers will not be able to
  follow the CNAME trick in the resolving chain and will fail to
  reverse-resolve your machine.  This can result in the service
  assigning it an incorrect access class, deny access or something along
  those lines.  If you stumble into such a service the only solution
  (that I know of) is for your ISP to insert your PTR record directly
  into their trick classless zone file instead of the trick CNAME
  record.


  Some ISPs will offer other ways to handle this, like Web based forms
  for you to input your reverse-mappings in or other automagical
  systems.
  5.  A real domain example

  Where we list some real zone files


  Users have suggested that I include a real example of a working domain
  as well as the tutorial example.


  I use this example with permission from David Bullock of LAND-5.
  These files were current 24th of September 1996, and were then edited
  to fit bind 8 restrictions and use extensions by me.  So, what you see
  here differs a bit from what you find if you query LAND-5's name
  servers now.


  5.1.  /etc/named.conf (or /var/named/named.conf)

  Here we find master zone sections for the two reverse zones needed:
  the 127.0.0 net, as well as LAND-5's 206.6.177 subnet. And a primary
  line for land-5's forward zone land-5.com. Also note that instead of
  stuffing the files in a directory called pz, as I do in this HOWTO, he
  puts them in a directory called zone.


  ______________________________________________________________________
  // Boot file for LAND-5 name server

  options {
          directory "/var/named";
  };

  zone "." {
          type hint;
          file "root.hints";
  };

  zone "0.0.127.in-addr.arpa" {
          type master;
          file "zone/127.0.0";
  };

  zone "land-5.com" {
          type master;
          file "zone/land-5.com";
  };

  zone "177.6.206.in-addr.arpa" {
          type master;
          file "zone/206.6.177";
  };
  ______________________________________________________________________



  If you put this in your named.conf file to play with PLEASE put
  ``notify no;'' in the zone sections for the two land-5 zones so as to
  avoid accidents.


  5.2.  /var/named/root.hints

  Keep in mind that this file is dynamic, and the one listed here is
  old. You're better off using one produced now, with dig, as explained
  earlier.
  ______________________________________________________________________
  ; <<>> DiG 8.1 <<>> @A.ROOT-SERVERS.NET.
  ; (1 server found)
  ;; res options: init recurs defnam dnsrch
  ;; got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10
  ;; flags: qr aa rd; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 13
  ;; QUERY SECTION:
  ;;      ., type = NS, class = IN

  ;; ANSWER SECTION:
  .                     6D IN NS        G.ROOT-SERVERS.NET.
  .                     6D IN NS        J.ROOT-SERVERS.NET.
  .                     6D IN NS        K.ROOT-SERVERS.NET.
  .                     6D IN NS        L.ROOT-SERVERS.NET.
  .                     6D IN NS        M.ROOT-SERVERS.NET.
  .                     6D IN NS        A.ROOT-SERVERS.NET.
  .                     6D IN NS        H.ROOT-SERVERS.NET.
  .                     6D IN NS        B.ROOT-SERVERS.NET.
  .                     6D IN NS        C.ROOT-SERVERS.NET.
  .                     6D IN NS        D.ROOT-SERVERS.NET.
  .                     6D IN NS        E.ROOT-SERVERS.NET.
  .                     6D IN NS        I.ROOT-SERVERS.NET.
  .                     6D IN NS        F.ROOT-SERVERS.NET.

  ;; ADDITIONAL SECTION:
  G.ROOT-SERVERS.NET.     5w6d16h IN A    192.112.36.4
  J.ROOT-SERVERS.NET.     5w6d16h IN A    198.41.0.10
  K.ROOT-SERVERS.NET.     5w6d16h IN A    193.0.14.129
  L.ROOT-SERVERS.NET.     5w6d16h IN A    198.32.64.12
  M.ROOT-SERVERS.NET.     5w6d16h IN A    202.12.27.33
  A.ROOT-SERVERS.NET.     5w6d16h IN A    198.41.0.4
  H.ROOT-SERVERS.NET.     5w6d16h IN A    128.63.2.53
  B.ROOT-SERVERS.NET.     5w6d16h IN A    128.9.0.107
  C.ROOT-SERVERS.NET.     5w6d16h IN A    192.33.4.12
  D.ROOT-SERVERS.NET.     5w6d16h IN A    128.8.10.90
  E.ROOT-SERVERS.NET.     5w6d16h IN A    192.203.230.10
  I.ROOT-SERVERS.NET.     5w6d16h IN A    192.36.148.17
  F.ROOT-SERVERS.NET.     5w6d16h IN A    192.5.5.241

  ;; Total query time: 215 msec
  ;; FROM: roke.uio.no to SERVER: A.ROOT-SERVERS.NET.  198.41.0.4
  ;; WHEN: Sun Feb 15 01:22:51 1998
  ;; MSG SIZE  sent: 17  rcvd: 436
  ______________________________________________________________________



  5.3.  /var/named/zone/127.0.0

  Just the basics, the obligatory SOA record, and a record that maps
  127.0.0.1 to localhost.  Both are required.  No more should be in this
  file.  It will probably never need to be updated, unless your
  nameserver or hostmaster address changes.



  ______________________________________________________________________
  @               IN      SOA     land-5.com. root.land-5.com. (
                                  199609203       ; Serial
                                  28800   ; Refresh
                                  7200    ; Retry
                                  604800  ; Expire
                                  86400)  ; Minimum TTL
                          NS      land-5.com.

  1                       PTR     localhost.
  ______________________________________________________________________



  5.4.  /var/named/zone/land-5.com

  Here we see the mandatory SOA record, the needed NS records.  We can
  see that he has a secondary name server at ns2.psi.net.  This is as it
  should be, always have a off site secondary server as backup.  We can
  also see that he has a master host called land-5 which takes care of
  many of the different Internet services, and that he's done it with
  CNAMEs (a alternative is using A records).


  As you see from the SOA record, the zone file originates at
  land-5.com, the contact person is root@land-5.com. hostmaster is
  another oft used address for the contact person.  The serial number is
  in the customary yyyymmdd format with todays serial number appended;
  this is probably the sixth version of zone file on the 20th of
  September 1996.  Remember that the serial number must increase
  monotonically, here there is only one digit for todays serial#, so
  after 9 edits he has to wait until tomorrow before he can edit the
  file again.  Consider using two digits.



  ______________________________________________________________________
  @       IN      SOA     land-5.com. root.land-5.com. (
                          199609206       ; serial, todays date + todays serial #
                          8H              ; refresh, seconds
                          2H              ; retry, seconds
                          1W              ; expire, seconds
                          1D )            ; minimum, seconds
                  NS      land-5.com.
                  NS      ns2.psi.net.
                  MX      10 land-5.com.  ; Primary Mail Exchanger
                  TXT     "LAND-5 Corporation"

  localhost       A       127.0.0.1

  router          A       206.6.177.1

  land-5.com.     A       206.6.177.2
  ns              A       206.6.177.3
  www             A       207.159.141.192

  ftp             CNAME   land-5.com.
  mail            CNAME   land-5.com.
  news            CNAME   land-5.com.

  funn            A       206.6.177.2

  ;
  ;       Workstations
  ;
  ws-177200       A       206.6.177.200
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177201       A       206.6.177.201
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177202       A       206.6.177.202
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177203       A       206.6.177.203
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177204       A       206.6.177.204
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177205       A       206.6.177.205
                  MX      10 land-5.com.   ; Primary Mail Host
  ; {Many repetitive definitions deleted - SNIP}
  ws-177250       A       206.6.177.250
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177251       A       206.6.177.251
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177252       A       206.6.177.252
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177253       A       206.6.177.253
                  MX      10 land-5.com.   ; Primary Mail Host
  ws-177254       A       206.6.177.254
                  MX      10 land-5.com.   ; Primary Mail Host
  ______________________________________________________________________



  If you examine land-5s nameserver you will find that the host names
  are of the form ws_number.  As of late bind 4 versions named started
  enforcing the restrictions on what characters may be used in host
  names.  So that does not work with bind-8 at all, and I substituted
  '-' (dash) for '_' (underline) for use in this HOWTO.


  Another thing to note is that the workstations don't have individual
  names, but rather a prefix followed by the two last parts of the IP
  numbers.  Using such a convention can simplify maintenance
  significantly, but can be a bit impersonal, and, in fact, be a source
  of irritation among your customers.


  We also see that funn.land-5.com is an alias for land-5.com, but using
  an A record, not a CNAME record.  This is a good policy as noted
  earlier.


  5.5.  /var/named/zone/206.6.177

  I'll comment on this file below


  ______________________________________________________________________
  @               IN      SOA     land-5.com. root.land-5.com. (
                                  199609206       ; Serial
                                  28800   ; Refresh
                                  7200    ; Retry
                                  604800  ; Expire
                                  86400)  ; Minimum TTL
                          NS      land-5.com.
                          NS      ns2.psi.net.
  ;
  ;       Servers
  ;
  1       PTR     router.land-5.com.
  2       PTR     land-5.com.
  2       PTR     funn.land-5.com.
  ;
  ;       Workstations
  ;
  200     PTR     ws-177200.land-5.com.
  201     PTR     ws-177201.land-5.com.
  202     PTR     ws-177202.land-5.com.
  203     PTR     ws-177203.land-5.com.
  204     PTR     ws-177204.land-5.com.
  205     PTR     ws-177205.land-5.com.
  ; {Many repetitive definitions deleted - SNIP}
  250     PTR     ws-177250.land-5.com.
  251     PTR     ws-177251.land-5.com.
  252     PTR     ws-177252.land-5.com.
  253     PTR     ws-177253.land-5.com.
  254     PTR     ws-177254.land-5.com.
  ______________________________________________________________________



  The reverse zone is the bit of the setup that seems to cause the most
  grief.  It is used to find the host name if you have the IP number of
  a machine.  Example: you are an IRC server and accept connections from
  IRC clients.  However you are a Norwegian IRC server and so you only
  want to accept connections from clients in Norway and other
  Scandinavian countries.  When you get a connection from a client the C
  library is able to tell you the IP number of the connecting machine
  because the IP number of the client is contained in all the packets
  that are passed over the network.  Now you can call a function called
  gethostbyaddr that looks up the name of a host given the IP number.
  Gethostbyaddr will ask a DNS server, which will then traverse the DNS
  looking for the machine.  Supposing the client connection is from
  ws-177200.land-5.com.  The IP number the C library provides to the IRC
  server is 206.6.177.200.  To find out the name of that machine we need
  to find 200.177.6.206.in-addr.arpa.  The DNS server will first find
  the arpa. servers, then find in-addr.arpa.  servers, following the
  reverse trail through 206, then 6 and at last finding the server for
  the 177.6.206.in-addr.arpa zone at LAND-5.  From which it will finally
  get the answer that for 200.177.6.206.in-addr.arpa we have a ``PTR
  ws-177200.land-5.com'' record, meaning that the name that goes with
  206.6.177.200 is ws-177200.land-5.com.  As with the explanation of how
  prep.ai.mit.edu is looked up, this is slightly fictitious.


  Getting back to the IRC server example.  The IRC server only accepts
  connections from the Scandinavian countries, i.e., *.no, *.se, *.dk,
  the name ws-177200.land-5.com clearly does not match any of those, and
  the server will deny the connection.  If there was no reverse mapping
  of 206.2.177.200 through the in-addr.arpa zone the server would have
  been unable to find the name at all and would have to settle to
  comparing 206.2.177.200 with *.no, *.se and *.dk, none of which will
  match.


  Some people will tell you that reverse lookup mappings are only
  important for servers, or not important at all.  Not so: Many ftp,
  news, IRC and even some http (WWW) servers will not accept connections
  from machines of which they are not able to find the name.  So reverse
  mappings for machines are in fact mandatory.


  6.  Maintenance

  Keeping it working.


  There is one maintenance task you have to do on nameds, other than
  keeping them running.  That's keeping the root.hints file updated.
  The easiest way is using dig, first run dig with no arguments, you
  will get the root.hints according to your own server.  Then ask one of
  the listed root servers with dig @rootserver.  You will note that the
  output looks terribly like a root.hints file.  Save it to a file (dig
  @e.root-servers.net . ns >root.hints.new) and replace the old
  root.hints with it.


  Remember to reload named after replacing the cache file.


  Al Longyear sent me this script, that can be run automatically to
  update root.hints, install a crontab entry to run it once a month and
  forget it.  The script assumes you have mail working and that the
  mail-alias `hostmaster' is defined.  You must hack it to suit your
  setup.



  ______________________________________________________________________
  #!/bin/sh
  #
  # Update the nameserver cache information file once per month.
  # This is run automatically by a cron entry.
  #
  # Original by Al Longyear
  # Updated for bind 8 by Nicolai Langfeldt
  # Miscelanious error-conditions reported by David A. Ranch
  # Ping test suggested by Martin Foster
  #
  (
   echo "To: hostmaster <hostmaster>"
   echo "From: system <root>"
   echo "Subject: Automatic update of the root.hints file"
   echo

   PATH=/sbin:/usr/sbin:/bin:/usr/bin:
   export PATH
   cd /var/named

   # Are we online?  Ping a server at your ISP
   case `ping -qnc some.machine.net` in
     *'100% packet loss'*)
          echo "The network is DOWN. root.hints NOT updated"
          echo
          exit 0
          ;;
   esac

   dig @rs.internic.net . ns >root.hints.new 2>&1

   case `cat root.hints.new` in
     *NOERROR*)
          # It worked
          :;;
     *)
          echo "The root.hints file update has FAILED."
          echo "This is the dig output reported:"
          echo
          cat root.hints.new
          exit 0
          ;;
   esac

   echo "The root.hints file has been updated to contain the following
  information:"
   echo
   cat root.hints.new

   chown root.root root.hints.new
   chmod 444 root.hints.new
   rm -f root.hints.old
   mv root.hints root.hints.old
   mv root.hints.new root.hints
   ndc restart
   echo
   echo "The nameserver has been restarted to ensure that the update is complete."
   echo "The previous root.hints file is now called
  /var/named/root.hints.old."
  ) 2>&1 | /usr/lib/sendmail -t
  exit 0
  ______________________________________________________________________



  Some of you might have picked up that the root.hints file is also
  available by ftp from Internic.  Please don't use ftp to update
  root.hints, the above method is much more friendly to the net, and
  Internic.


  7.  Converting from version 4 to version 8

  This was originally a section on using bind 8 written by David E.
  Smith (dave@bureau42.ml.org).  I have edited it some to fit the new
  section name.


  There's not much to it. Except for using named.conf instead of
  named.boot, everything is identical. And bind8 comes with a perl
  script that converts old-style files to new. Example named.boot (old
  style) for a cache-only name server:


  ______________________________________________________________________
  directory /var/named
  cache   .                                     root.hints
  primary 0.0.127.IN-ADDR.ARPA                    127.0.0.zone
  primary localhost                               localhost.zone
  ______________________________________________________________________



  On the command line, in the bind8/src/bin/named directory (this
  assumes you got a source distribution.  If you got a binary package
  the script is probably around, I'm not sure where it would be though.
  -ed.), type:


  ______________________________________________________________________
  ./named-bootconf.pl < named.boot > named.conf
  ______________________________________________________________________



  Which creates named.conf:


  ______________________________________________________________________
  // generated by named-bootconf.pl

  options {
          directory "/var/named";
  };

  zone "." {
          type hint;
          file "root.hints";
  };

  zone "0.0.127.IN-ADDR.ARPA" {
          type master;
          file "127.0.0.zone";
  };

  zone "localhost" {
          type master;
          file "localhost.zone";
  };
  ______________________________________________________________________

  It works for everything that can go into a named.boot file, although
  it doesn't add all of the new enhancements and configuration options
  that bind8 allows.  Here's a more complete named.conf that does the
  same things, but a little more efficiently.


  ______________________________________________________________________
  // This is a configuration file for named (from BIND 8.1 or later).
  // It would normally be installed as /etc/named.conf.
  // The only change made from the `stock' named.conf (aside from this
  // comment :) is that the directory line was uncommented, since I
  // already had the zone files in /var/named.

  options {
          directory "/var/named";
          datasize 20M;
  };

  zone "localhost" IN {
          type master;
          file "localhost.zone";
  };

  zone "0.0.127.in-addr.arpa" IN {
          type master;
          file "127.0.0.zone";
  };

  zone "." IN {
          type hint;
          file "root.hints";
  };
  ______________________________________________________________________



  In the bind 8 distributions directory bind8/src/bin/named/test you
  find this, and copies of the zone files, that many people can just
  drop in and use instantly.


  The formats for zone files and root.hints files are identical, as are
  the commands for updating them.


  8.  Questions and Answers

  Please read this section before mailing me.


  1. My named wants a named.boot file


     You are reading the wrong HOWTO.  Please see the old version of
     this HOWTO, which covers bind 4, at
     http://www.math.uio.no/~janl/DNS/


  2. How do use DNS from inside a firewall?


     A hint: forward only;, You will probably also need



     ___________________________________________________________________
       query-source port 53;

     ___________________________________________________________________



  inside the ``options'' part of the named.conf file as suggested in the
  example ``caching'' section.


  3. How do I make DNS rotate through the available addresses for a
     service, say www.busy.site to obtain a load balancing effect, or
     similar?


     Make several A records for www.busy.site and use bind 4.9.3 or
     later.  Then bind will round-robin the answers.  It will not work
     with earlier versions of bind.


  4. I want to set up DNS on a (closed) intranet.  What do I do?


     You drop the root.hints file and just do zone files.  That also
     means you don't have to get new hint files all the time.


  5. How do I set up a secondary (slave) name server?


     If the primary/master server has address 127.0.0.1 you put a line
     like this in the named.conf file of your secondary:


     ___________________________________________________________________
       zone "linux.bogus" {
             type slave;
             file "sz/linux.bogus";
             masters { 127.0.0.1; };
       };

     ___________________________________________________________________



  You may list several alternate master servers the zone can be copied
  from inside the masters list, separated by ';' (semicolon).


  6. I want bind running when I'm disconnected from the net.


     There are three items regarding this:


  o  I have received this mail from Ian Clark <ic@deakin.edu.au> where
     he explains his way of doing this:



  I run named on my 'Masquerading' machine here. I have
  two root.hints files, one called root.hints.real which contains
  the real root server names and the other called root.hints.fake
  which contains...

  ----
  ; root.hints.fake
  ; this file contains no information
  ----

  When I go off line I copy the root.hints.fake file to root.hints and
  restart named.

  When I go online I copy root.hints.real to root.hints and restart
  named.

  This is done from ip-down & ip-up respectively.

  The first time I do a query off line on a domain name named doesn't
  have details for it puts an entry like this in messages..

  Jan 28 20:10:11 hazchem named[10147]: No root nameserver for class IN

  which I can live with.

  It certainly seems to work for me. I can use the nameserver for
  local machines while off the 'net without the timeout delay for
  external domain names and I while on the 'net queries for external
  domains work normally



  o  I have also received information about how bind interacts with NFS
     and the portmapper on a mostly offline machine from Karl-Max
     Wanger:



       I use to run my own named on all my machines which are only
       occasionally connected to the Internet by modem. The nameserver only
       acts as a cache, it has no area of authority and asks back for
       everything at the name servers in the root.cache file. As is usual with
       Slackware, it is started before nfsd and mountd.

       With one of my machines (a Libretto 30 notebook) I had the problem
       that sometimes I could mount it from another system connected to my
       local LAN, but most of the time it didn't work.  I had the same effect
       regardless of using PLIP, a PCMCIA ethernet card or PPP over a serial
       interface.

       After some time of guessing and experimenting I found out that
       apparently named messed with the process of registration nfsd and
       mountd have to carry out with the portmapper upon startup (I start
       these daemons at boot time as usual). Starting named after nfsd and
       mountd eliminated this problem completely.

       As there are no disadvantages to expect from such a modified boot
       sequence I'd advise everybody to do it that way to prevent potential
       trouble.



  o  Finally, there is HOWTO information about this at Ask Mr. DNS at
     http://www.acmebw.com/askmrdns/#linux-ns.  It is about bind 4
     though, so you have to adapt what he says to bind 8.



  7. Where does the caching name server store its cache? Is there any
     way I can control the size of the cache?


     The cache is completely stored in memory, it is not written to disk
     at any time.  Every time you kill named the cache is lost.  The
     cache is not controllable in any way.  named manages it according
     to some simple rules and that is it.  You cannot control the cache
     or the cache size in any way for any reason. If you want to you can
     ``fix'' this by hacking named.  This is however not recommended.


  8. Does named save the cache between restarts?  Can I make it save it?


     No, named does not save the cache when it dies.  That means that
     the cache must be built anew each time you kill and restart named.
     There is no way to make named save the cache in a file.  If you
     want you can ``fix'' this by hacking named.  This is however not
     recommended.


  9. How can I get a domian? I want to set up my own domain called (for
     example) linux-rules.net.  How can I get the domain I want assigned
     to me?


     Please contact your network service provider.  They will be able to
     help you with this.  Please note that in most parts of the world
     you need to pay money to get a domain.



  9.  How to become a bigger time DNS admin.

  Documentation and tools.


  Real Documentation exists.  Online and in print.  The reading of
  several of these is required to make the step from small time DNS
  admin to a big time one.  In print the standard book is DNS and BIND
  by C. Liu and P. Albitz from O'Reilly & Associates, Sebastopol, CA,
  ISBN 0-937175-82-X.  I read this, it's excellent, though based on bind
  4, this is not a real problem though.  There is also a section in on
  DNS in TCP/IP Network Administration, by Craig Hunt from O'Reilly...,
  ISBN 0-937175-82-X.  Another must for Good DNS administration (or good
  anything for that matter) is Zen and the Art of Motorcycle Maintenance
  by Robert M. Pirsig :-) Available as ISBN 0688052304 and others.


  Online you will find stuff on  <http://www.dns.net/dnsrd/> (DNS
  Resources Directory),  <http://www.isc.org/bind.html>; A FAQ, a
  reference manual (BOG; Bind Operations Guide) as well as papers and
  protocol definitions and DNS hacks (these, and most, if not all, of
  the RFCs mentioned below, are also contained in the bind
  distribution).  I have not read most of these, but then I'm not a big-
  time DNS admin either.  Arnt Gulbrandsen on the other hand has read
  BOG and he's ecstatic about it :-).  The newsgroup comp.protocols.tcp-
  ip.domains is about DNS.  In addition there are a number of RFCs about
  DNS, the most important are probably these:



     RFC 2052
        A. Gulbrandsen, P. Vixie, A DNS RR for specifying the location
        of services (DNS SRV), October 1996


     RFC 1918
        Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de Groot, E. Lear,
        Address Allocation for Private Internets, 02/29/1996.


     RFC 1912
        D. Barr, Common DNS Operational and Configuration Errors,
        02/28/1996.


     RFC 1912 Errors
        B. Barr Errors in RFC 1912, this is available at
        <http://www.cis.ohio-state.edu/~barr/rfc1912-errors.html>


     RFC 1713
        A. Romao, Tools for DNS debugging, 11/03/1994.


     RFC 1712
        C. Farrell, M. Schulze, S. Pleitner, D. Baldoni, DNS Encoding of
        Geographical Location, 11/01/1994.


     RFC 1183
        R. Ullmann, P. Mockapetris, L. Mamakos, C. Everhart, New DNS RR
        Definitions, 10/08/1990.


     RFC 1035
        P. Mockapetris, Domain names - implementation and specification,
        11/01/1987.


     RFC 1034
        P. Mockapetris, Domain names - concepts and facilities,
        11/01/1987.


     RFC 1033
        M. Lottor, Domain administrators operations guide, 11/01/1987.


     RFC 1032
        M. Stahl, Domain administrators guide, 11/01/1987.


     RFC 974
        C. Partridge, Mail routing and the domain system, 01/01/1986.



