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<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><option>-4</option></arg>
  <arg><option>-6</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>.  Transfer the zone printing out the NS, PTR
and address records (A/AAAA).  If combined with <option>-a</option>
all records will be printed.  
</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>-4</option> option forces <command>host</command> to only
use IPv4 query transport.  The <option>-6</option> option forces
<command>host</command> to only use IPv6 query transport.
</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.  If a query type of IXFR is chosen the starting
serial number can be specified by appending an equal followed by the
starting serial number (e.g. -t IXFR=12345678).
</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>
