dig — DNS lookup utility
dig [@server] [-b ] [address-c ] [class-f ] [filename-k ] [filename-m] [-p ] [port#-q ] [name-t ] [type-v] [-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. If no usable server addresses
are found, dig will send the query to the local
host.
When no command line arguments or options are given, dig 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
domain names. Either use the -t and
-c options to specify the type and class,
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; if an
address is found there, it queries the name server at
that address. If either of the -4 or
-6 options are in use, then
only addresses for the corresponding transport
will be tried. If no usable addresses are found,
dig will send the query to the
local host. 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 organized in
the same way they would be presented as queries to
dig using the command-line interface.
The -m option enables memory usage debugging.
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 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 is useful to distinguish the
name from other arguments.
The -v causes dig to
print the version number and exit.
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]aaflag
A synonym for +[no]aaonly.
+[no]aaonlySets the "aa" flag in the query.
+[no]additionalDisplay [do not display] the additional section of a reply. The default is to display it.
+[no]adflagSet [do not set] the AD (authentic data) bit in the query. This requests the server to return whether all of the answer and authority sections have all been validated as secure according to the security policy of the server. AD=1 indicates that all records have been validated as secure and the answer is not from a OPT-OUT range. AD=0 indicate that some part of the answer was insecure or not validated. This bit is set by default.
+[no]allSet or clear all display flags.
+[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]besteffortAttempt to display the contents of messages which are malformed. The default is to not display malformed answers.
+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.
+[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]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]commentsToggle the display of comment lines in the output. The default is to print comments.
+[no]cryptoToggle the display of cryptographic fields in DNSSEC records. The contents of these field are unnecessary to debug most DNSSEC validation failures and removing them makes it easier to see the common failures. The default is to display the fields. When omitted they are replaced by the string "[omitted]" or in the DNSKEY case the key id is displayed as the replacement, e.g. "[ key id = value ]".
+[no]defname
Deprecated, treated as a synonym for
+[no]search
+[no]dnssecRequests DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT record in the additional section of the query.
+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]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. EDNS is set to
0 by default.
+[no]expireSend an EDNS Expire option.
+[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 behavior.
+[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]ignoreIgnore truncation in UDP responses instead of retrying with TCP. By default, TCP retries are performed.
+[no]keepopen
Keep the TCP socket open between queries and reuse
it rather than creating a new TCP socket for each
lookup. The default is +nokeepopen.
+[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.
+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 if
+search is set.
+[no]nsidInclude an EDNS name server ID request when sending a query.
+[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]onesoaPrint only one (starting) SOA record when performing an AXFR. The default is to print both the starting and ending SOA records.
+[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]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.
+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.
+[no]rrcommentsToggle the display of per-record comments in the output (for example, human-readable key information about DNSKEY records). The default is not to print record comments unless multiline mode is active.
+[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.
'ndots' from resolv.conf (default 1)
which may be overridden by +ndots
determines if the name will be treated as relative
or not and hence whether a search is eventually
performed or not.
+[no]shortProvide a terse answer. The default is to print the answer in a verbose form.
+[no]showsearchPerform [do not perform] a search showing intermediate results.
+[no]sigchaseChase DNSSEC signature chains. Requires dig be compiled with -DDIG_SIGCHASE.
+[no]sit[=####]
Send a Source Identity Token EDNS option, with optional
value. Replaying a SIT from a previous response will
allow the server to identify a previous client. The
default is +nosit. Currently using
experimental value 65001 for the option code.
+split=W
Split long hex- or base64-formatted fields in resource
records into chunks of W
characters (where W is rounded
up to the nearest multiple of 4).
+nosplit or
+split=0 causes fields not to
be split at all. The default is 56 characters, or
44 characters when multiline mode is active.
+[no]statsThis 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]subnet=addr/prefixSend an EDNS Client Subnet option with the specified IP address or network prefix.
+[no]tcp
Use [do not use] TCP when querying name servers. The
default behavior is to use UDP unless an
ixfr=N query is requested, in which
case the default is TCP. AXFR queries always use
TCP.
+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.
+[no]topdownWhen chasing DNSSEC signature chains perform a top-down validation. Requires dig be compiled with -DDIG_SIGCHASE.
+[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.
+dnssec is also set when +trace is set to better emulate the default queries from a nameserver.
+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.
+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]ttlidDisplay [do not display] the TTL when printing the record.
+[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".
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.
BIND 9.10.2-P2