dig Command
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. |
Parameters
| Item | Description |
|---|---|
| global-queryopt... | Global query option (see Multiple Queries). |
| query | Query option (see Query Options). |
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]tcpis 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
+searchoption 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
+nssearchor+tracequery 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
+shortoption 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 timeout 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 +noqrIDN 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- 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 |