Use IPv4 only for query transport. See also the -6 option.

Use IPv6 only for query transport. See also the -4 option.

"All". The -a option is normally equivalent to -v -t ANY. It also affects the behaviour of the -l list zone option.

"Almost all". The -A option is equivalent to -a except RRSIG, NSEC, and NSEC3 records are omitted from the output.

Query class: This can be used to lookup HS (Hesiod) or CH (Chaosnet) class resource records. The default class is IN (Internet).

Check consistency: host will query 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.

Print debugging traces. Equivalent to the -v verbose option.

Obsolete. Use the IP6.INT domain for reverse lookups of IPv6 addresses as defined in RFC1886 and deprecated in RFC4159. The default is to use IP6.ARPA as specified in RFC3596.

List zone: The host command performs a zone transfer of zone name and prints out the NS, PTR and address records (A/AAAA).

Together, the -l -a options print all records in the zone.

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.

Non-recursive query: Setting this option clears the RD (recursion desired) bit in the query. 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 can be referrals to other name servers.

Number of retries for UDP queries: If number is negative or zero, the number of retries will default to 1. The default value is 1, or the value of the attempts option in /etc/resolv.conf, if set.

Do not send the query to the next nameserver if any server responds with a SERVFAIL response, which is the reverse of normal stub resolver behavior.

Query type: The type argument can be any recognized query type: CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc.

When no query type is specified, host automatically selects an appropriate query type. By default, it looks for A, AAAA, and MX records. If the -C option is given, queries will be made for SOA records. 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 (like -t IXFR=12345678).

TCP/UDP: 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. Type ANY queries default to TCP but can be forced to UDP initially using -U.

Memory usage debugging: the flag can be record, usage, or trace. You can specify the -m option more than once to set multiple flags.

Verbose output. Equivalent to the -d debug option. Verbose output can also be enabled by setting the debug option in /etc/resolv.conf.

Print the version number and exit.

Wait forever: The query timeout is set to the maximum possible. See also the -W option.

Timeout: Wait for up to wait seconds for a reply. If wait is less than one, the wait interval is set to one second.

By default, host will wait for 5 seconds for UDP responses and 10 seconds for TCP connections. These defaults can be overridden by the timeout option in /etc/resolv.conf.

See also the -w option.