host

host
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Name

host — DNS lookup utility

Synopsis

host [-aCdlnrsTwv] [-c class] [-N ndots] [-R number] [-t type] [-W wait] [-m flag] [-4] [-6] {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 provided for backwards - compatibility. In previous versions, the -d option - switched on debugging traces and -v enabled verbose - output. -

- List mode is selected by the -l option. This makes - host perform a zone transfer for zone - name. Transfer the zone printing out - the NS, PTR - and address records (A/AAAA). If combined with -a - all records will be printed. -

- The -i - 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. -

- 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, 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. - Setting 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 behavior 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 -4 option forces host to only - use IPv4 query transport. The -6 option forces - host to only use IPv6 query transport. -

- The -t option is used to select the query type. - type can be any recognized 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. 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). -

- 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 - 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. -

- The -s option tells host - not to send the query to the next nameserver - if any server responds with a SERVFAIL response, which is the - reverse of normal stub resolver behavior. -

- The -m can be used to set the memory usage debugging - flags - record, usage and - trace. -

IDN SUPPORT

- If host has been built with IDN (internationalized - domain name) support, it can accept and display non-ASCII domain names. - host appropriately converts character encoding of - domain name before sending a request to DNS server or displaying a - reply from the server. - If you'd like to turn off the IDN support for some reason, defines - the IDN_DISABLE environment variable. - The IDN support is disabled if the variable is set when - host runs. -

FILES

/etc/resolv.conf -

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Name

Synopsis

DESCRIPTION

IDN SUPPORT

FILES

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