dig - Online in the Cloud

PROGRAM:

NAME

dig - DNS lookup utility

SYNOPSIS

dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m] [-p port#]
[-q name] [-t type] [-v] [-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. If no usable server addresses are found, dig will send the query to
the local host.

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 domain 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; if an address is
found there, it queries the name server at that address. If either of the -4 or -6
options are in use, then only addresses for the corresponding transport will be tried.
If no usable addresses are found, dig will send the query to the local host. 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

-4
Use IPv4 only.

-6
Use IPv6 only.

-b address[#port]
Set the source IP address of the query. The address 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>"

-c class
Set the query class. The default class is IN; other classes are HS for Hesiod records
or CH for Chaosnet records.

-f file
Batch mode: dig reads a list of lookup requests to process from the given file. Each
line in the file should be organized in the same way they would be presented as
queries to dig using the command-line interface.

-i
Do reverse IPv6 lookups using the obsolete RFC1886 IP6.INT domain, which is no longer
in use. Obsolete bit string label queries (RFC2874) are not attempted.

-k keyfile
Sign queries using TSIG using a key read from the given file. Key files can be
generated using tsig-keygen(8). 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.

-m
Enable memory usage debugging.

-p port
Send the query to a non-standard port on the server, instead of the defaut port 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.

-q name
The domain name to query. This is useful to distinguish the name from other arguments.

-t type
The resource record type to query. 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, set the type 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.

-v
Print the version number and exit.

-x addr
Simplified reverse lookups, for mapping addresses to names. The addr is an IPv4
address in dotted-decimal notation, or a colon-delimited IPv6 address. When the -x is
used, there is no need to provide the name, class and type arguments. dig
automatically performs a lookup for a name like 94.2.0.192.in-addr.arpa and sets the
query type and class to PTR and IN respectively. IPv6 addresses are looked up using
nibble format under the IP6.ARPA domain (but see also the -i option).

-y [hmac:]keyname:secret
Sign queries using TSIG with the given authentication key. keyname is the name of the
key, and secret is the base64 encoded shared secret. hmac is the name of the key
algorithm; valid choices are hmac-md5, hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, or hmac-sha512. If hmac is not specified, the default is hmac-md5.

NOTE: You should use the -k option and avoid the -y option, because with -y the shared
secret is supplied as a command line argument in clear text. This may be visible in
the output from ps(1) or in a history file maintained by the user's shell.

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. Keywords may be abbreviated, provided the abbreviation is
unambiguous; for example, +cd is equivalent to +cdflag. The query options are:

+[no]aaflag
A synonym for +[no]aaonly.

+[no]aaonly
Sets the "aa" flag in the query.

+[no]additional
Display [do not display] the additional section of a reply. The default is to display
it.

+[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. This bit is set
by default.

+[no]all
Set or clear all display flags.

+[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]besteffort
Attempt to display the contents of messages which are malformed. The default is to not
display malformed answers.

+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.

+[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]class
Display [do not display] the CLASS when printing the record.

+[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]comments
Toggle the display of comment lines in the output. The default is to print comments.

+[no]crypto
Toggle the display of cryptographic fields in DNSSEC records. The contents of these
field are unnecessary to debug most DNSSEC validation failures and removing them makes
it easier to see the common failures. The default is to display the fields. When
omitted they are replaced by the string "[omitted]" or in the DNSKEY case the key id
is displayed as the replacement, e.g. "[ key id = value ]".

+[no]defname
Deprecated, treated as a synonym for +[no]search

+[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.

+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]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. EDNS is set to 0 by default.

+[no]ednsflags[=#]
Set the must-be-zero EDNS flags bits (Z bits) to the specified value. Decimal, hex and
octal encodings are accepted. Setting a named flag (e.g. DO) will silently be ignored.
By default, no Z bits are set.

+[no]ednsnegotiation
Enable / disable EDNS version negotiation. By default EDNS version negotiation is
enabled.

+[no]ednsopt[=code[:value]]
Specify EDNS option with code point code and optionally payload of value as a
hexadecimal string. +noednsopt clears the EDNS options to to be sent.

+[no]expire
Send an EDNS Expire option.

+[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]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]ignore
Ignore truncation in UDP responses instead of retrying with TCP. By default, TCP
retries are performed.

+[no]keepopen
Keep the TCP socket open between queries and reuse it rather than creating a new TCP
socket for each lookup. The default is +nokeepopen.

+[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.

+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 if +search is set.

+[no]nsid
Include an EDNS name server ID request when sending a query.

+[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]onesoa
Print only one (starting) SOA record when performing an AXFR. The default is to print
both the starting and ending SOA records.

+[no]opcode=value
Set [restore] the DNS message opcode to the specified value. The default value is
QUERY (0).

+[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]rdflag
A synonym for +[no]recurse.

+[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.

+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.

+[no]rrcomments
Toggle the display of per-record comments in the output (for example, human-readable
key information about DNSKEY records). The default is not to print record comments
unless multiline mode is active.

+[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.

´ndots' from resolv.conf (default 1) which may be overridden by +ndots determines if
the name will be treated as relative or not and hence whether a search is eventually
performed or not.

+[no]short
Provide a terse answer. The default is to print the answer in a verbose form.

+[no]showsearch
Perform [do not perform] a search showing intermediate results.

+[no]sigchase
Chase DNSSEC signature chains. Requires dig be compiled with -DDIG_SIGCHASE.

+[no]sit[=####]
Send a Source Identity Token EDNS option, with optional value. Replaying a SIT from a
previous response will allow the server to identify a previous client. The default is
+nosit. Currently using experimental value 65001 for the option code.

+split=W
Split 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 at all. The default is 56 characters, or 44 characters
when multiline mode is active.

+[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]subnet=addr/prefix
Send an EDNS Client Subnet option with the specified IP address or network prefix.

+[no]tcp
Use [do not use] TCP when querying name servers. The default behavior is to use UDP
unless an ixfr=N query is requested, in which case the default is TCP. AXFR queries
always use TCP.

+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.

+[no]topdown
When chasing DNSSEC signature chains perform a top-down validation. Requires dig be
compiled with -DDIG_SIGCHASE.

+[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.

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
nameserver.

+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.

+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]ttlid
Display [do not display] the TTL when printing the record.

+[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".

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.

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