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Commands Reference, Volume 2
dig Command
Purpose
DNS lookup utility
Syntax
dig [@server]
[-b address] [-c class] [-f filename] [-k filename] [ -n ][-p port#] [-t type] [-x addr] [-y name:key] [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 queried name server(s). Most
DNS administrators use dig 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, 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).
Flags
-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. |
-c class |
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. |
-f filename |
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. |
-h |
A brief summary of its command-line arguments and options
is printed when the -h option is given. |
-k filename |
To sign the DNS queries sent by dig and their responses using transaction signatures (TSIG), specify a TSIG
key file using the -k option. |
-n |
By default, IPv6 addresses are looked up using the IP6.ARPA
domain and binary labels as defined in RFC2874. To use the older RFC1886 method
using the IP6.INT domain and nibble labels, specify
the -n (nibble) option. |
-p port# |
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. |
-t type |
Sets the query type to type. It can be any valid query type which 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, 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. |
-x addr |
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. |
-y name:key |
You can also specify the TSIG key itself on the command
line using the -y option; 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. |
Parameters
global-queryopt... |
Global query option. |
query |
Query. |
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 search list or domain
directive in resolv.conf (if any). The search list is
not used by default.
- +[no]defname
- Deprecated, treated as a synonym for +[no]search
- +[no]aaonly
- This option does nothing. It is provided for compatibility with old
versions of dig where it sets an unimplemented resolver
flag.
- +[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]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, 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 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=A
- Sets the number of times to retry UDP queries to server to A instead of the default, 3. If A is less
than or equal to zero, the number of retries is silently rounded up to 1.
- +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.
- +[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.
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.
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, 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
- 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.
Files
Related Information
The host and dnssec-keygen commands.
The named8 daemon.
RFC1035
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