User Commands HOST(1)



NAME
host - DNS lookup utility

SYNOPSIS
host [ -aCdlnrTwv ] [ -c class ] [ -N ndots ] [ -R number
] [ -t type ] [ -W wait ] name [ server ]

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

name 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 host will by default perform a
reverse lookup for that address. server is an optional
argument which is either the name or IP address of the name
server that host should query instead of the server or
servers listed in /etc/resolv.conf.

The -a (all) option is equivalent to setting the -v option
and asking host to make a query of type ANY.

When the -C option is used, host will attempt to display the
SOA records for zone name 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.

The -c option instructs to make a DNS query of class class.
This can be used to lookup Hesiod or Chaosnet class resource
records. The default class is IN (Internet).

Verbose output is generated by host when the -d or -v option
is used. The two options are equivalent. They have been pro-
vided for backwards compatibility. In previous versions, the
-d option switched on debugging traces and -v enabled ver-
bose output.

List mode is selected by the -l option. This makes host per-
form a zone transfer for zone name. The argument is provided
for compatibility with older implementations. This option is
equivalent to making a query of type AXFR.

The -n option specifies that reverse lookups of IPv6
addresses should use the IP6.INT domain and "nibble" labels
as defined in RFC1886. The default is to use IP6.ARPA and
binary labels as defined in RFC2874.

The -N option sets the number of dots that have to be in
name for it to be considered absolute. The default value is
that defined using the ndots statement in /etc/resolv.conf,



BIND9 Last change: Jun 30, 2000 1






User Commands HOST(1)



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 search or domain directive in
/etc/resolv.conf.

The number of UDP retries for a lookup can be changed with
the -R option. number indicates how many times host will
repeat a query that does not get answered. The default
number of retries is 1. If number is negative or zero, the
number of retries will default to 1.

Non-recursive queries can be made via the -r option. Set-
ting this option clears the RD - recursion desired - bit in
the query which host makes. This should mean that the name
server receiving the query will not attempt to resolve name.
The -r option enables host 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.

By default host uses UDP when making queries. The -T 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.

The -t option is used to select the query type. type can be
any recognised query type: CNAME, NS, SOA, SIG, KEY, AXFR,
etc. When no query type is specified, host automatically
selects an appropriate query type. By default it looks for A
records, but if the -C option was given, queries will be
made for SOA records, and if name is a dotted-decimal IPv4
address or colon-delimited IPv6 address, host will query for
PTR records.

The time to wait for a reply can be controlled through the
-W and -w options. The -W option makes host wait for wait
seconds. If wait is less than one, the wait interval is set
to one second. When the -w option is used, host will effec-
tively 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.

FILES
/etc/resolv.conf

SEE ALSO
dig(1), named(8).








BIND9 Last change: Jun 30, 2000 2