<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN">

<refentry>

<refentryinfo>

<date>Jun 30, 2000</date>

</refentryinfo>

<refmeta>

<refentrytitle>host</refentrytitle>

<manvolnum>1</manvolnum>

<refmiscinfo>BIND9</refmiscinfo>

</refmeta>

<refnamediv>

<refname>host</refname>

<refpurpose>DNS lookup utility</refpurpose>

</refnamediv>

<refsynopsisdiv>

<cmdsynopsis>

<command>host</command>

<arg><option>-aCdlnrTwv</option></arg>

<arg><option>-c <replaceable class="parameter">class</replaceable></option></arg>

<arg><option>-N <replaceable class="parameter">ndots</replaceable></option></arg>

<arg><option>-R <replaceable class="parameter">number</replaceable></option></arg>

<arg><option>-t <replaceable class="parameter">type</replaceable></option></arg>

<arg><option>-W <replaceable class="parameter">wait</replaceable></option></arg>

<arg choice=req>name</arg>

<arg choice=opt>server</arg>

</cmdsynopsis>

</refsynopsisdiv>

<refsect1>

<title>DESCRIPTION</title>

<para>

<command>host</command>

is a simple utility for performing DNS lookups.

It is normally used to convert names to IP addresses and vice versa.

When no arguments or options are given,

<command>host</command>

prints a short summary of its command line arguments and options.

</para>

<para>

<parameter>name</parameter> is the domain name that is to be looked

up. It can also be a dotted-decimal IPv4 address or a colon-delimited

IPv6 address, in which case <command>host</command> will by default

perform a reverse lookup for that address.

<parameter>server</parameter> is an optional argument which is either

the name or IP address of the name server that <command>host</command>

should query instead of the server or servers listed in

<filename>/etc/resolv.conf</filename>.

</para>

<para>

The <option>-a</option> (all) option is equivalent to setting the

<option>-v</option> option and asking <command>host</command> to make

a query of type ANY.

</para>

<para>

When the <option>-C</option> option is used, <command>host</command>

will attempt to display the SOA records for zone

<parameter>name</parameter> from all the listed authoritative name

servers for that zone. The list of name servers is defined by the NS

records that are found for the zone.

</para>

<para>

The <option>-c</option> option instructs to make a DNS query of class

<parameter>class</parameter>. This can be used to lookup Hesiod or

Chaosnet class resource records. The default class is IN (Internet).

</para>

<para>

Verbose output is generated by <command>host</command> when the

<option>-d</option> or <option>-v</option> option is used. The two

options are equivalent. They have been provided for backwards

compatibility. In previous versions, the <option>-d</option> option

switched on debugging traces and <option>-v</option> enabled verbose

output.

</para>

<para>

List mode is selected by the <option>-l</option> option. This makes

<command>host</command> perform a zone transfer for zone

<parameter>name</parameter>. The argument is provided for

compatibility with older implemementations. This option is equivalent

to making a query of type AXFR.

</para>

<para>

The <option>-i</option>

option specifies that reverse lookups of IPv6 addresses should

use the IP6.INT domain as defined in RFC1886.

The default is to use IP6.ARPA.

</para>

<para>

The <option>-N</option> option sets the number of dots that have to be

in <parameter>name</parameter> for it to be considered absolute. The

default value is that defined using the ndots statement in

<filename>/etc/resolv.conf</filename>, or 1 if no ndots statement is

present. Names with fewer dots are interpreted as relative names and

will be searched for in the domains listed in the <type>search</type>

or <type>domain</type> directive in

<filename>/etc/resolv.conf</filename>.

</para>

<para>

The number of UDP retries for a lookup can be changed with the

<option>-R</option> option. <parameter>number</parameter> indicates

how many times <command>host</command> will repeat a query that does

not get answered. The default number of retries is 1. If

<parameter>number</parameter> is negative or zero, the number of

retries will default to 1.

</para>

<para>

Non-recursive queries can be made via the <option>-r</option> option.

Setting this option clears the <type>RD</type> &mdash; recursion

desired &mdash; bit in the query which <command>host</command> makes.

This should mean that the name server receiving the query will not

attempt to resolve <parameter>name</parameter>. The

<option>-r</option> option enables <command>host</command> to mimic

the behaviour of a name server by making non-recursive queries and

expecting to receive answers to those queries that are usually

referrals to other name servers.

</para>

<para>

By default <command>host</command> uses UDP when making queries. The

<option>-T</option> option makes it use a TCP connection when querying

the name server. TCP will be automatically selected for queries that

require it, such as zone transfer (AXFR) requests.

</para>

<para>

The <option>-t</option> option is used to select the query type.

<parameter>type</parameter> can be any recognised query type: CNAME,

NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,

<command>host</command> automatically selects an appropriate query

type. By default it looks for A records, but if the

<option>-C</option> option was given, queries will be made for SOA

records, and if <parameter>name</parameter> is a dotted-decimal IPv4

address or colon-delimited IPv6 address, <command>host</command> will

query for PTR records.

</para>

<para>

The time to wait for a reply can be controlled through the

<option>-W</option> and <option>-w</option> options. The

<option>-W</option> option makes <command>host</command> wait for

<parameter>wait</parameter> seconds. If <parameter>wait</parameter>

is less than one, the wait interval is set to one second. When the

<option>-w</option> option is used, <command>host</command> will

effectively wait forever for a reply. The time to wait for a response

will be set to the number of seconds given by the hardware's maximum

value for an integer quantity.

</para>

</refsect1>

<refsect1>

<title>FILES</title>

<para>

<filename>/etc/resolv.conf</filename>

</para>

</refsect1>

<refsect1>

<title>SEE ALSO</title>

<para>

<citerefentry>

<refentrytitle>dig</refentrytitle><manvolnum>1</manvolnum>

</citerefentry>,

<citerefentry>

<refentrytitle>named</refentrytitle><manvolnum>8</manvolnum>

</citerefentry>.

</para>

</refsect1>

</refentry>