dig — DNS lookup utility
dig [@server] [-b ] [address-c ] [class-f ] [filename-k ] [filename-p ] [port#-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 BIND9 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:
dig @server name type
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.
nameis 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 "::". An optional
port
may be specified by appending "#<port>"
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 organised in
the same way they would be presented as queries to
dig using the command-line interface.
If a non-standard port number is to be queried, the
-p option is used. port# is
the port number that dig will send its
queries
instead of the standard DNS port number 53. This option would be used
to test a name server that has been configured to listen for queries
on a non-standard port number.
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 BIND9. The default query type "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 distingish 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]tcpUse [do not use] TCP when querying name servers. The default behaviour 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]ignoreIgnore 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]showsearchPerform [do not perform] a search showing intermediate results.
+[no]defname
Deprecated, treated as a synonym for +[no]search
+[no]aaonlySets the "aa" flag in the query.
+[no]aaflag
A synonym for +[no]aaonly.
+[no]adflagSet [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]cdflagSet [do not set] the CD (checking disabled) bit in the query. This requests the server to not perform DNSSEC validation of responses.
+[no]clDisplay [do not display] the CLASS when printing the record.
+[no]ttlidDisplay [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]nssearchWhen 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]traceToggle 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]cmdtoggles 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]shortProvide 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]commentsToggle the display of comment lines in the output. The default is to print comments.
+[no]statsThis query option toggles the printing of statistics: when the query was made, the size of the reply and so on. The default behaviour is to print the query statistics.
+[no]qrPrint [do not print] the query as it is sent. By default, the query is not printed.
+[no]questionPrint [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]answerDisplay [do not display] the answer section of a reply. The default is to display it.
+[no]authorityDisplay [do not display] the authority section of a reply. The default is to display it.
+[no]additionalDisplay [do not display] the additional section of a reply. The default is to display it.
+[no]allSet or clear all display flags.
+time=T
Sets the timeout for a query to
T seconds. The default time
out 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]multilinePrint 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]failDo 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 behaviour.
+[no]besteffortAttempt to display the contents of messages which are malformed. The default is to not display malformed answers.
+[no]dnssecRequests DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT record in the additional section of the query.
+[no]sigchaseChase 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.
+[no]topdownWhen 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.