dig - DNS lookup utility
dig
[@server] [ -b address]
[-c class]
[-f filename] [
-k filename] [
-q name] [ -t type]
[-x addr]
[-y [hmac:]name:key] [-4]
[-6] [name] [type] [class] [queryopt...]
dig
[-h]
dig
[global-queryopt...] [query...]
dig (domain information groper) is a flexible tool for interrogating DNS
name servers. It performs DNS lookups and displays the answers that are
returned from the name server(s) that were queried. Most DNS administrators
use
dig to troubleshoot DNS problems because of its flexibility, ease
of use and clarity of output. Other lookup tools tend to have less
functionality than
dig.
Although
dig is normally used with command-line arguments, it also has a
batch mode of operation for reading lookup requests from a file. A brief
summary of its command-line arguments and options is printed when the
-h option is given. Unlike earlier versions, the BIND 9 implementation
of
dig allows multiple lookups to be issued from the command line.
Unless it is told to query a specific name server,
dig will try each of
the servers listed in
/etc/resolv.conf.
When no command line arguments or options are given, will perform an NS query
for "." (the root).
It is possible to set per-user defaults for
dig via
${HOME}/.digrc. This file is read and any options in it are applied
before the command line arguments.
The IN and CH class names overlap with the IN and CH top level domains names.
Either use the
-t and
-c options to specify the type and class
or use the
-q the specify the domain name or use "IN." and
"CH." when looking up these top level domains.
A typical invocation of
dig looks like:
where:
server
is the name or IP address of the name server
to query. This can be an IPv4 address in dotted-decimal notation or an IPv6
address in colon-delimited notation. When the supplied server argument
is a hostname, dig resolves that name before querying that name server.
If no server argument is provided, dig consults
/etc/resolv.conf and queries the name servers listed there. The reply
from the name server that responds is displayed.
name
is the name of the resource record that is to
be looked up.
type
indicates what type of query is required
— ANY, A, MX, SIG, etc. type can be any valid query type. If no
type argument is supplied, dig will perform a lookup for an A
record.
The
-b option sets the source IP address of the query to
address.
This must be a valid address on one of the host's network interfaces or
"0.0.0.0" or "::".
The default query class (IN for internet) is overridden by the
-c option.
class is any valid class, such as HS for Hesiod records or CH for
Chaosnet records.
The
-f option makes
dig operate in batch mode by reading a list
of lookup requests to process from the file
filename. The file contains
a number of queries, one per line. Each entry in the file should be organized
in the same way they would be presented as queries to
dig using the
command-line interface.
The
-4 option forces
dig to only use IPv4 query transport. The
-6 option forces
dig to only use IPv6 query transport.
The
-t option sets the query type to
type. It can be any valid
query type which is supported in BIND 9. The default query type is
"A", unless the
-x option is supplied to indicate a reverse
lookup. A zone transfer can be requested by specifying a type of AXFR. When an
incremental zone transfer (IXFR) is required,
type is set to ixfr=N.
The incremental zone transfer will contain the changes made to the zone since
the serial number in the zone's SOA record was
N.
The
-q option sets the query name to
name. This useful do
distinguish the
name from other arguments.
Reverse lookups — mapping addresses to names — are simplified by
the
-x option.
addr is an IPv4 address in dotted-decimal
notation, or a colon-delimited IPv6 address. When this option is used, there
is no need to provide the
name,
class and
type arguments.
dig automatically performs a lookup for a name like
11.12.13.10.in-addr.arpa and sets the query type and class to PTR and IN
respectively. By default, IPv6 addresses are looked up using nibble format
under the IP6.ARPA domain. To use the older RFC1886 method using the IP6.INT
domain specify the
-i option. Bit string labels (RFC2874) are now
experimental and are not attempted.
To sign the DNS queries sent by
dig and their responses using transaction
signatures (TSIG), specify a TSIG key file using the
-k option. You can
also specify the TSIG key itself on the command line using the
-y
option;
hmac is the type of the TSIG, default HMAC-MD5,
name is
the name of the TSIG key and
key is the actual key. The key is a
base-64 encoded string, typically generated by
dnssec-keygen(8).
Caution should be taken when using the
-y option on multi-user systems
as the key can be visible in the output from
ps(1) or in the shell's
history file. When using TSIG authentication with
dig, the name server
that is queried needs to know the key and algorithm that is being used. In
BIND, this is done by providing appropriate
key and
server
statements in
named.conf.
dig provides a number of query options which affect the way in which
lookups are made and the results displayed. Some of these set or reset flag
bits in the query header, some determine which sections of the answer get
printed, and others determine the timeout and retry strategies.
Each query option is identified by a keyword preceded by a plus sign (+). Some
keywords set or reset an option. These may be preceded by the string no to
negate the meaning of that keyword. Other keywords assign values to options
like the timeout interval. They have the form
+keyword=value. The query
options are:
+[no]tcp
Use [do not use] TCP when querying name
servers. The default behavior is to use UDP unless an AXFR or IXFR query is
requested, in which case a TCP connection is used.
+[no]vc
Use [do not use] TCP when querying name
servers. This alternate syntax to +[no]tcp is provided for backwards
compatibility. The "vc" stands for "virtual
circuit".
+[no]ignore
Ignore truncation in UDP responses instead of
retrying with TCP. By default, TCP retries are performed.
+domain=somename
Set the search list to contain the single
domain somename, as if specified in a domain directive in
/etc/resolv.conf, and enable search list processing as if the
+search option were given.
+[no]search
Use [do not use] the search list defined by
the searchlist or domain directive in resolv.conf (if any). The search
list is not used by default.
+[no]showsearch
Perform [do not perform] a search showing
intermediate results.
+[no]defname
Deprecated, treated as a synonym for
+[no]search
+[no]aaonly
Sets the "aa" flag in the
query.
+[no]aaflag
A synonym for +[no]aaonly.
+[no]adflag
Set [do not set] the AD (authentic data) bit
in the query. The AD bit currently has a standard meaning only in responses,
not in queries, but the ability to set the bit in the query is provided for
completeness.
+[no]cdflag
Set [do not set] the CD (checking disabled)
bit in the query. This requests the server to not perform DNSSEC validation of
responses.
+[no]cl
Display [do not display] the CLASS when
printing the record.
+[no]ttlid
Display [do not display] the TTL when printing
the record.
+[no]recurse
Toggle the setting of the RD (recursion
desired) bit in the query. This bit is set by default, which means dig
normally sends recursive queries. Recursion is automatically disabled when the
+nssearch or +trace query options are used.
+[no]nssearch
When this option is set, dig attempts
to find the authoritative name servers for the zone containing the name being
looked up and display the SOA record that each name server has for the
zone.
+[no]trace
Toggle tracing of the delegation path from the
root name servers for the name being looked up. Tracing is disabled by
default. When tracing is enabled, dig makes iterative queries to
resolve the name being looked up. It will follow referrals from the root
servers, showing the answer from each server that was used to resolve the
lookup.
+[no]cmd
Toggles the printing of the initial comment in
the output identifying the version of dig and the query options that
have been applied. This comment is printed by default.
+[no]short
Provide a terse answer. The default is to
print the answer in a verbose form.
+[no]identify
Show [or do not show] the IP address and port
number that supplied the answer when the +short option is enabled. If
short form answers are requested, the default is not to show the source
address and port number of the server that provided the answer.
+[no]comments
Toggle the display of comment lines in the
output. The default is to print comments.
+[no]stats
This query option toggles the printing of
statistics: when the query was made, the size of the reply and so on. The
default behavior is to print the query statistics.
+[no]qr
Print [do not print] the query as it is sent.
By default, the query is not printed.
+[no]question
Print [do not print] the question section of a
query when an answer is returned. The default is to print the question section
as a comment.
+[no]answer
Display [do not display] the answer section of
a reply. The default is to display it.
+[no]authority
Display [do not display] the authority section
of a reply. The default is to display it.
+[no]additional
Display [do not display] the additional
section of a reply. The default is to display it.
+[no]all
Set or clear all display flags.
+time=T
Sets the timeout for a query to T
seconds. The default timeout is 5 seconds. An attempt to set T to less
than 1 will result in a query timeout of 1 second being applied.
+tries=T
Sets the number of times to try UDP queries to
server to T instead of the default, 3. If T is less than or
equal to zero, the number of tries is silently rounded up to 1.
+retry=T
Sets the number of times to retry UDP queries
to server to T instead of the default, 2. Unlike +tries, this
does not include the initial query.
+ndots=D
Set the number of dots that have to appear in
name to D 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.
+bufsize=B
Set the UDP message buffer size advertised
using EDNS0 to B bytes. The maximum and minimum sizes of this buffer
are 65535 and 0 respectively. Values outside this range are rounded up or down
appropriately. Values other than zero will cause a EDNS query to be
sent.
+edns=#
Specify the EDNS version to query with. Valid
values are 0 to 255. Setting the EDNS version will cause a EDNS query to be
sent. +noedns clears the remembered EDNS version.
+[no]multiline
Print records like the SOA records in a
verbose multi-line format with human-readable comments. The default is to
print each record on a single line, to facilitate machine parsing of the
dig output.
+[no]fail
Do not try the next server if you receive a
SERVFAIL. The default is to not try the next server which is the reverse of
normal stub resolver behavior.
+[no]besteffort
Attempt to display the contents of messages
which are malformed. The default is to not display malformed answers.
+[no]dnssec
Requests DNSSEC records be sent by setting the
DNSSEC OK bit (DO) in the OPT record in the additional section of the
query.
+[no]sigchase
Chase DNSSEC signature chains. Requires dig be
compiled with -DDIG_SIGCHASE.
+trusted-key=####
Specifies a file containing trusted keys to be
used with
+sigchase. Each DNSKEY record must be on its own line.
If not specified
dig will look for
/etc/trusted-key.key then
trusted-key.key in the current directory.
Requires dig be compiled with -DDIG_SIGCHASE.
When chasing DNSSEC signature chains perform a
top-down validation. Requires dig be compiled with -DDIG_SIGCHASE.
The BIND 9 implementation of
dig supports specifying multiple queries on
the command line (in addition to supporting the
-f batch file option).
Each of those queries can be supplied with its own set of flags, options and
query options.
In this case, each
query argument represent an individual query in the
command-line syntax described above. Each consists of any of the standard
options and flags, the name to be looked up, an optional query type and class
and any query options that should be applied to that query.
A global set of query options, which should be applied to all queries, can also
be supplied. These global query options must precede the first tuple of name,
class, type, options, flags, and query options supplied on the command line.
Any global query options (except the
+[no]cmd option) can be overridden
by a query-specific set of query options. For example:
dig +qr www.isc.org any -x 127.0.0.1 isc.org ns +noqr
shows how
dig could be used from the command line to make three lookups:
an ANY query for www.isc.org, a reverse lookup of 127.0.0.1 and a query for
the NS records of isc.org. A global query option of
+qr is applied, so
that
dig shows the initial query it made for each lookup. The final
query has a local query option of
+noqr which means that
dig
will not print the initial query when it looks up the NS records for isc.org.
If
dig has been built with IDN (internationalized domain name) support,
it can accept and display non-ASCII domain names.
dig 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
dig
runs.
/etc/resolv.conf
${HOME}/.digrc
host(1),
named(8),
dnssec-keygen(8), RFC1035.
There are probably too many query options.
Copyright © 2004-2007 Internet Systems Consortium, Inc. ("ISC")
Copyright © 2000-2003 Internet Software Consortium.
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