Purpose
DNS lookup utility.
Syntax
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...]
Description
The dig (domain information
groper) command is a flexible tool for interrogating DNS name servers.
It performs DNS lookups and displays the answers that are returned
from the queried name server(s). Most DNS administrators use the dig command to troubleshoot DNS problems because of its flexibility,
ease of use, and clarity of output. Although dig is normally
used with command-line arguments, it also has a batch mode for reading
lookup requests from a file. 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, the dig command tries each of the servers listed in the /etc/resolv.conf file. If you specify no command line arguments or options, the dig command performs an NS query for "." (the root).
It is possible to set per-user defaults for the dig command
through the ${HOME}/.digrc file. The dig command reads
this file and applies any options in it before the command line arguments.
The IN and CH class names overlap with the IN and CH top level domains names. When you look up these top
level domains, you can either use the -t and -c options
to specify the type and class or use the -q option to specify
the domain name or use the IN and CH names.
Flags
| Item |
Description |
|---|
| -b address |
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 "::". You can specify an optional port by appending
"#port". |
| -c class |
Overrides the default query class (IN for internet).
The class parameter value is any valid class, such as
HS for Hesiod records or CH for CHAOSNET records. |
| -f filename |
Makes the dig command operate in batch
mode by reading a list of lookup requests to process from the specified
file name. The file contains a number of queries; one per line. Each
entry in the file must be organized in the same way they are presented
as queries to the dig command using the command-line interface. |
| -h |
Prints a brief summary of command-line arguments
and options. |
| -k filename |
Specifies a TSIG key file using the -k option to sign the DNS queries sent by the dig command. |
| -p port# |
Queries a non-standard port number. The port# parameter value is the port number that the dig command sends
its queries to instead of the standard DNS port number 53. You can
use this option to test a name server that has been configured to
listen for queries on a non-standard port number. |
| -q name |
Distinguishes the name from other arguments.
Sets the query name to the name parameter value specified. |
| -t type |
Sets the query type to the type parameter value. It can be any valid query type that is supported
in BIND9. 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, the type parameter value is set to ixfr=N. The incremental zone
transfer contains the changes made to the zone because the serial
number in the zone's SOA record was N. |
| -x addr |
Simplifies reverse lookups (mapping addresses
to names). The addr parameter value is an IPv4 address
in dotted-decimal notation, or a colon-delimited IPv6 address. When
you use this option, there is no need to provide the name, class, and type arguments. The dig command 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. |
| -y [hmac:] name:key |
Specifies the TSIG key itself on the command
line; hmac is the type of the TSIG. The default value is HMAC-MD5.
The name parameter value is the name of the TSIG key
and the key parameter value is the actual key. The key
is a base-64 encoded string, typically generated by dnssec-keygen(8). Caution must 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 the dig command, 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 the named.conf file. |
| -4 |
Forces the dig command to only use the
IPv4 query transport. |
| -6 |
Forces the dig command to only use the
IPv6 query transport. |
Query Options
The
dig command provides a number of query options that 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 can
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 or 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 or 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 the /etc/resolv.conf file, and enable search list processing as if the +search option was given.
- +[no]search
- Use or do not use the search list defined by the search list or
domain directive in the /etc/resolv.conf file (if any). The
search list is not used by default.
- +[no]defname
- Deprecated, treated as a synonym for +[no]search.
- +[no]aaonly
- Sets the "aa" flag in the query.
- +[no]adflag
- Set or 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 or 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 or do not display the CLASS when printing the record.
- +[no]ttlid
- Display or do not display the TTL when printing the record.
- +[no]recursive
- 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, the dig command 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, the dig command makes iterative queries
to resolve the name being looked up. It follows referrals from the
root servers, showing the answer from each server that was used to
resolve the lookup.
- +[no]cmd
- Toggle 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
- Toggle 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 or do not print the query as it is sent. By default, the
query is not printed.
- +[no]question
- Print or 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 or do not display the answer section of a reply. The default
is to display it.
- +[no]authority
- Display or do not display the authority section of a reply. The
default is to display it.
- +[no]additional
- Display or 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
- Set the timeout for a query to T seconds. The default
time out is 5 seconds. An attempt to set the T parameter
value to less than 1 results in a query timeout of 1 second being
applied.
- +tries=A
- Set the number of times to try UDP queries to server to the A parameter value instead of the default, 3. If the A parameter value is less than or equal to zero, the number
of retries is silently rounded up to 1.
- +retry=T
- Set the number of times to retry UDP queries to server to the T parameter value 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 the D parameter value as it is considered absolute. The default
value is one that is defined using the ndots statement in the /etc/resolv.conf file, or 1 if no ndots statement is present.
Names with fewer dots are interpreted as relative names and is searched
for in the domains listed in the search or domain directive in the /etc/resolv.conf file.
- +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 of this range are rounded
up or down appropriately. Values other than zero cause an EDNS query
to be sent.
- +edns=#
- Specify the EDNS version to query with. Valid values are 0 to
255. Setting the EDNS version causes 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 not to try the next server which is the reverse of normal stub
resolver behavior.
- +[no]besteffort
- Attempt to display the contents of messages that are malformed.
The default is not to display malformed answers.
- +[no]dnssec
- Request DNSSEC records to 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. Require the dig command
to be compiled with -DDIG SIGCHASE.
- +trusted-key=####
- Specify a file containing trusted keys to be used with +sigchase. Each DNSKEY record must be on its own line. If not specified, the dig command looks for the /etc/trusted-key.key file then
the trusted-key.key file in the current directory. Require
the dig command to be compiled with -DDIG SIGCHASE.
- +[no]topdown
- When chasing DNSSEC signature chains, perform a top down validation.
Require the dig command to be compiled with -DDIG SIGCHASE.
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 represents
an individual query in the command-line syntax. Each consists of any
of the standard options and flags, the name to be looked up, an optional
query type, class, and any query options that must be applied to that
query.
A global set of query options,
which must 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
This
dig command string shows how the
dig command 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 the
dig command shows the initial
query it made for each lookup. The final query has a local query option
of
+noqr, which means that the
dig command does not
print the initial query when it looks up the NS records for
isc.org.
IDN SUPPORT
If the dig command has
been built with internationalized domain name (IDN) support, it can
accept and display non-ASCII domain names. The dig command
appropriately converts character encoding of domain name before sending
a request to the DNS server or displaying a reply from the server.
If you would like to turn off the IDN support for some reason, define
the IDN DISABLE environment variable; the following IDN support is
disabled if the variable is set when the dig command runs.
Examples
A typical invocation of
dig looks like:
dig @server name type
where:
- server
- 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, the dig command resolves that name before querying that name server.
If no server argument is provided, the dig command consults
the /etc/resolv.conf file and queries the name servers listed
there. The reply from the name server that responds is displayed.
- name
- The name of the resource record that is to be looked up.
- type
- Indicates what type of query is required — ANY, A, MX, SIG, and so on. The type argument value
can be any valid query type. If no type argument is supplied,
the dig command performs a lookup for an A record.
Files
| Item |
Description |
|---|
| /etc/resolv.conf |
|
| ${HOME}/.digrc |
|