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### 4. The Host resolution tab

### 4.1 What is it?

The Host resolution tab allows the execution of a host resolution program (`host(1)` or `nslookup(8)`). This host resolution program will asks the Domain Name Server the answer to the question asked.

### 4.2 Description

This command looks for information about Internet hosts and domain names. It gets this information from a set of interconnected servers that are spread across the world. This set of interconnected servers are called the Domain Name Servers (DNS). The information is stored in the form of resource records belonging to hierarchically organized zones.

By default, the command simply converts between host names and Internet addresses. However, with the Search for options, it can be used to find all of the information about domain names that is maintained by the domain nameserver system. The information printed consists of various fields of the associated resource records that were retrieved.

The host field can be either host names (domain names) or numeric Internet addresses.

A numeric Internet address consists of four decimal numbers separated by dots, e.g. `192.16.199.1`, representing the four bytes of the 32-bit address. The default action is to look up the associated host name.

A host name or domain name consists of component names (labels) separated by dots, e.g. `nikhefh.nikhef.nl`. The default action is to look up all of its Internet addresses.

For single names without a trailing dot, the local domain is automatically tacked on the end. Thus a user in domain `nikhef.nl` can type in `nikhapo`, and it will actually look up `nikhapo.nikhef.nl`. In all other cases, the name is tried unchanged. Single names with trailing dot are considered top-level domain specifications, e.g. `nl.`

For a more precise description of the behaviour of this command, please see the underlying program's man-page `host(1)` or `nslookup(8)`.

### 4.3 Options

Search for

  This allows you to specify a particular type of resource record information to be looked up. Supported types are listed below.

Server

  This is the name (or the address) of the domain name server to ask.

#### Resource type

The resource type possible are:

`A` ___ the host's Internet address.

`PTR` _ the host name.

`NS` __ the name server for the named zone.

`MX` __ the mail exchanger.

`CNAME` the canonical name for an alias.

`SOA` _ the domain's ``start-of-authority'' information.

`ANY` _ all informations available.

#### Host's authors

This program is originally from Rutgers University. It has been rewritten by Eric Wassenaar, NIKHEF, <e07@nikhef.nl>.

#### NsLookup's authors

Andrew Cherenson

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