NAME
dig - DNS lookup utility
SYNOPSIS
dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m]
[-p port#] [-q name] [-t type] [-x addr] [-y [hmac:]name:key] [-4]
[-6] [name] [type] [class] [queryopt...]
dig [-h]
dig [global-queryopt...] [query...]
DESCRIPTION
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, 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 domains
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.
SIMPLE USAGE
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.
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.
OPTIONS
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 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.
QUERY OPTIONS
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. 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.
+[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.
+[no]topdown
When chasing DNSSEC signature chains perform a top-down validation.
Requires dig be compiled with -DDIG_SIGCHASE.
+[no]nsid
Include an EDNS name server ID request when sending a query.
MULTIPLE QUERIES
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.
IDN SUPPORT
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.
FILES
/etc/resolv.conf
${HOME}/.digrc
SEE ALSO
host(1), named(8), dnssec-keygen(8), RFC1035.
BUGS
There are probably too many query options.
COPYRIGHT
Copyright (C) 2004-2009 Internet Systems Consortium, Inc. ("ISC")
Copyright (C) 2000-2003 Internet Software Consortium.