dnsquery(1Mtcp)

dnsquery -- query domain name servers using resolver

Synopsis

dnsquery [-n nameserver] [-t type] [-c class] [-r retry] [-p retry_period] [-d] [-s] [-v] host

Description

The dnsquery program is a general interface to nameservers via BIND resolver library calls. The program supports queries to the nameserver with an opcode of QUERY. This program is intended to replace or supplement programs like nslookup(1Mtcp). All arguments except for host and nameserver are treated without case-sensitivity.

The options are as follows:

-n nameserver

The nameserver to be used in the query. Nameservers can appear either as Internet addresses of the form w.x.y.z or as domain names. The default is specified in /etc/resolv.conf.

-t type

The type of resource record of interest. Types include:

A: address
NS: nameserver
CNAME: canonical name
PTR: domain name pointer
SOA: start of authority
WKS: well-known service
HINFO: host information
MINFO: mailbox information
MX: mail exchange
RP: responsible person
MG: mail group member
AFSDB: DCE or AFS server
ANY: wildcard

Note that any case may be used. The default is ANY.

-c class

The class of resource records of interest. Classes include:

IN: Internet
HS: Hesiod
CHAOS: Chaos
ANY: wildcard

Note that any case may be used. The default is IN.

-r retry

The number of times to retry if the nameserver is not responding. The default is 4.

-p retry_period

The period to wait before timing out. The default is RES_TIMEOUT.

-d

Turn on debugging. This sets the RES_DEBUG bit of the resolver's ``options'' field. The default is no debugging.

-s

Use a stream rather than a packet. This uses a TCP stream connection with the nameserver rather than a UDP datagram. This sets the RES_USEVC bit of the resolver's ``options'' field. The default is to use UDP.

-v

Synonym for -s.

host

The name of the host (or domain) of interest.

Queries of a class other than IN can have unpredicable results since ordinarily a nameserver only has a list of root nameservers for class IN resource records.

Query uses a call to inet_addr(3N) to determine if the argument for the -n option is a valid Internet address. Unfortunately, inet_addr seems to cause a segmentation fault with some (bad) addresses (for example, 1.2.3.4.5).

Files

/etc/resolv.conf: to get the default nameserver and search lists
arpa/nameser.h: list of usable RR types and classes
resolv.h: list of resolver flags

Diagnostics

If the resolver fails to answer the query and debugging has not been turned on, dnsquery will simply print a message similar to:

   Query failed (rc = 1) : Unknown host

The value of the return code is supplied by h_errno.

References

nslookup(1Mtcp) named(1Mtcp) resolver(3N)