dig Command

Purpose

DNS lookup utility.

Syntax

dig [@server] [-b address] [-c class] [-f filename] [-k keyfile] [-m] [-p port#] [-q name] [-t type] [-u] [-v] [-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 servers. 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 no usable server addresses are found, the dig command sends the query to the local host. 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[#port]	Sets the source IP address of the query-to address. The specified address 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 keyfile	Specifies a TSIG key file using the -k option to sign the DNS queries sent by the dig command. You can generate key files by using the tsig-keygen command. When you use the TSIG authentication with the dig command, the name server that is queried must identify the key and algorithm that is being used. In BIND, this operation is performed by specifying appropriate key and server statements in the named.conf file.
-m	Enables memory usage debugging.
-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. All resource record types can be expressed as TYPEnn, where nn is the number of `type`. If the resource record type is not supported in BIND 9, the result is displayed as described in RFC 3597.
-u	Indicates that print query times must be specified in microseconds instead of milliseconds.
-v	Prints the version number and exits.
-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]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 or +[no]aaflag

Sets the "aa" flag in the query.

+[no]adflag

Set or do not set the AD (authentic data) bit in the query. This query requests the server to return whether all of the answer and authority sections have 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 an OPT-OUT range. AD=0 indicates that some part of the answer was insecure or not validated. This bit is set by default.

+[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]class

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. Addresses of servers that did not respond are also printed.

+[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.

If @server is also specified, it affects only the initial query for the root zone name servers. +dnssec is also set when +trace is set to better emulate the default queries from a name server.

+[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 option always has a global effect. It cannot be set globally and then overridden on a per-lookup basis. This comment is printed by default.

+[no]short

Provide a terse answer. The default is to print the answer in a verbose form. This option always has a global effect; it cannot be set globally and then overridden on a per-lookup basis.

+[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 with information about the packet header and options pseudo-section, and the names of the response section. Comments are displayed by default. Other types of comments in the output are not affected by this option, but can be controlled by using other command-line switches, such as +[no]cmd, +[no]question, +[no]stats, and +[no]rrcomments.

+[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.

+[no]badcookie

Retries the lookup operation with a new server cookie if a BADCOOKIE response is received.

+[no]cookie=####

Sets or does not set a COOKIE EDNS option, with an optional value. Replaying a COOKIE from a previous response allows the server to identify a previous client. The default value is +cookie. +cookie is also set when +trace is set to better emulate the default queries from a name server.

+bufsize[=B]

Sets the buffer size of the advertised UDP message by using EDNS0 to B bytes. The maximum and minimum sizes of this buffer are 65535 and 0. The +bufsize=0 query disables Extension Mechanisms for DNS (EDNS). Use +bufsize=0 +edns to send an EDNS message with an advertised size of 0 bytes. The +bufsize query restores the default buffer size.

+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.

+[no]crypto

Toggles the display of cryptographic fields in DNSSEC records. The contents of these fields are not required for debugging most DNSSEC validation failures. If you remove the cryptographic fields, you can easily view the common failures. The cryptographic fields are displayed by default. When these cryptographic fields are omitted, they are replaced by the string [omitted] or in case of DNSKEY, the key ID is displayed. For example: [key id = value].

+dscp=value

Sets the DSCP code point that must be used while sending the query. Valid DSCP code points are in the range 0 - 63. By default, no code point is explicitly set.

+[no]edns[=#]

Specifies the EDNS version to query. Valid values are in the range 0 - 255. Setting the EDNS version causes an EDNS query to be sent. +noedns clears the stored EDNS version information. EDNS is set to 0 by default.

+[no]ednsflags[=#]

Sets the must-be-zero EDNS flags bits (Z bits) to the specified value. Decimal, hex, and octal encoding are accepted. Setting a named flag (for example, DO) is silently ignored. By default, no Z bits are set.

+[no]ednsnegotiation

Enables or disables EDNS version negotiation. By default, EDNS version negotiation is enabled.

+[no]ednsopt[=code[:value]]

Specifies the EDNS option with code point and an optional payload with value as a hexadecimal string. code can be either an EDNS option name (for example, NSID or ECS) or an arbitrary numeric value. +noednsopt clears the EDNS options.

+[no]expire

Sends an EDNS Expire option.

+[no]header-only

Sends a query with a DNS header without a question section. The question section is added by default. The query type and query name are ignored when this option is set.

+[no]idnin

Processes or does not process IDN domain names based on input. This option requires IDN SUPPORT to be enabled at compile time. By default, IDN input is processed when standard output is a tty. The IDN processing based on input is disabled when the output of the dig command is redirected to files, pipes, and other non-tty file descriptors.

+[no]keepalive

Sends or does not send an EDNS keepalive option.

+[no]keepopen

Keeps or does not keep the TCP socket open between queries and reuses it instead of creating a new TCP socket for each lookup operation. The default value is +nokeepopen.

+[no]mapped

Allows or does not allow the usage of mapped IPv4-over-IPv6 addresses for DNS lookup. The default value is +mapped.

+[no]nsid

When enabled, includes an EDNS name server ID request while sending a query.

+[no]onesoa

When enabled, prints only one (starting) SOA record while performing an AXFR query. By default, both the starting and ending SOA records are printed.

+[no]opcode=value

When enabled, sets or restores the DNS message opcode to the specified value. The default value is QUERY (0).

+padding=value

Pads the size of the query packet by using the EDNS padding option to blocks of value bytes. For example, +padding=32 causes a 48-byte query to be padded with 64 bytes. The default block size is 0, which disables padding; the maximum value is 512. Values are typically expected to be powers of two, such as 128; however, it is not mandatory. Responses to padded queries might also be padded, but only if the query uses TCP or DNS COOKIE.

+[no]raflag

Sets or does not set the RA (recursion available) bit in the query. The default value is +noraflag. This bit is ignored by the server for QUERY.

+[no]rdflag

Similar to +[no]recurse.

+[no]recurse

Toggles the setting of the RD (recursion desired) bit in the query. This bit is set by default, which means the dig command typically sends recursive queries. Recursion is automatically disabled when the +nssearch or +trace query option is used.

+[no]rrcomments

Toggles the display of per-record comments in the output (for example, human-readable key information about DNSKEY records). By default, record comments are printed unless multi-line mode is active.

+[no]showsearch

Performs or does not perform a search showing intermediate results.

+split=W

Splits 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. The default value is 56 characters, or 44 characters when multi-line mode is active.

+[no]subnet=addr[/prefix-length]

Sends or does not send an EDNS CLIENT-SUBNET option with the specified IP address or network prefix.

dig +subnet=0.0.0.0/0, or simply dig +subnet=0 for short, sends an EDNS CLIENT-SUBNET option with an empty address and a source prefix-length of zero, which signals a resolver that the client’s address information must not be used when resolving this query.

+[no]tcflag

Sets or does not set the TC (TrunCation) bit in the query. The default value is +notcflag. This bit is ignored by the server for QUERY.

+timeout=T

Sets the timeout value for a query to T seconds. The default timeout value is 5 seconds. An attempt to set T to less than 1 is silently set to 1.

+tries=T

Sets the number of times to try UDP and TCP queries on a 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.

+[no]ttlunits

Displays or does not display the TTL in time units of s, m, h, d, and w, representing seconds, minutes, hours, days, and weeks. This implies +ttlid.

+[no]unexpected

Accepts or does not accept answers from unexpected sources. By default, the dig command will not accept a reply from a source other than the source to which it sent the query.

+[no]unknownformat

Prints all RDATA in unknown RR type presentation format (RFC 3597). By default, RDATA for known types is printed in the type’s presentation format.

+[no]yaml

When enabled, this option prints responses (and, if +qr is in use, also the outgoing queries) in a detailed YAML format.

+[no]zflag

Sets or does not set the last unassigned DNS header flag in a DNS query. This flag is set to off by default.

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

/etc/resolv.conf

${HOME}/.digrc