This tutorial explains Linux “dig” command, options and its usage with examples.
dig (domain information groper) is a network administration command-line tool for querying Domain Name System (DNS) name servers. Dig is useful for network troubleshooting and for educational purposes. Dig can operate in interactive command line mode or in batch mode by reading requests from an operating system file. When a specific name server is not specified in the command invocation, it will use the operating systems default resolver, usually configured via the resolv.conf file. Without any arguments it queries the DNS root zone.
Dig supports Internationalized Domain Name (IDN) queries. Dig is part of the BIND domain name server software suite. Dig replaces older tools such as nslookup and the host program.
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.
A typical invocation of dig looks like:
dig @server name type
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 and queries the name servers listed there. 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.
dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m] [-p port#] [-q name] [-t type] [-x addr] [-y [hmac:]name:key] [-4] [-6] [name] [type] [class] [queryopt…]
dig [global-queryopt…] [query…]
The -b option 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 “::”. An optional port may be specified by appending “#”
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.
The -f option 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.
The -m option enables memory usage debugging.
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.
The -4 option forces dig to only use IPv4 query transport. The -6 option forces dig to only use IPv6 query transport.
The -t option sets the query type to type. 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, 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.
The -q option sets the query name to name. This useful do distinguish the name from other arguments.
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 184.108.40.206.in-addr.arpa and sets the query type and class to PTR and IN respectively. By default, IPv6 addresses are looked up using nibble format under the IP6.ARPA domain.
To sign the DNS queries sent by dig and their responses using transaction signatures (TSIG), specify a TSIG key file using the -k option. You can also specify the TSIG key itself on the command line using the -y option; hmac is the type of the TSIG, default HMAC-MD5, name is the name of the TSIG key and key is the actual key.
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:
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.
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”.
Ignore truncation in UDP responses instead of retrying with TCP. By default, TCP retries are performed.
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.
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.
Perform [do not perform] a search showing intermediate results.
Deprecated, treated as a synonym for +[no]search
Sets the “aa” flag in the query.
A synonym for +[no]aaonly.
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.
Set [do not set] the CD (checking disabled) bit in the query. This requests the server to not perform DNSSEC validation of responses.
Display [do not display] the CLASS when printing the record.
Display [do not display] the TTL when printing the record.
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.
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.
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.
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.
Provide a terse answer. The default is to print the answer in a verbose form.
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.
Toggle the display of comment lines in the output. The default is to print comments.
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.
Print [do not print] the query as it is sent. By default, the query is not printed.
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.
Display [do not display] the answer section of a reply. The default is to display it.
Display [do not display] the authority section of a reply. The default is to display it.
Display [do not display] the additional section of a reply. The default is to display it.
Set or clear all display flags.
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.
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.
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.
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.
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.
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.
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.
Print only one (starting) SOA record when performing an AXFR. The default is to print both the starting and ending SOA records.
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.
Attempt to display the contents of messages which are malformed. The default is to not display malformed answers.
Requests DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT record in the additional section of the query.
Chase DNSSEC signature chains. Requires dig be compiled with -DDIG_SIGCHASE.
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.
When chasing DNSSEC signature chains perform a top-down validation. Requires dig be compiled with -DDIG_SIGCHASE.
Include an EDNS name server ID request when sending a query.
1. Trace Usage
See how domains are resolved using root servers i.e. turn on tracing of the delegation path from the root name servers for the name being looked up. When tracing is enabled, dig makes iterative queries to resolve the name being looked up.
$ dig +trace sanfoundry.com ; <> DiG 9.9.2-P1 <> +trace sanfoundry.com ;; global options: +cmd . 5 IN NS m.root-servers.net. . 5 IN NS k.root-servers.net. . 5 IN NS j.root-servers.net. . 5 IN NS c.root-servers.net. . 5 IN NS h.root-servers.net. . 5 IN NS i.root-servers.net. . 5 IN NS e.root-servers.net. . 5 IN NS b.root-servers.net. . 5 IN NS d.root-servers.net. . 5 IN NS a.root-servers.net. . 5 IN NS g.root-servers.net. . 5 IN NS f.root-servers.net. . 5 IN NS l.root-servers.net. ;; Received 512 bytes from 127.0.1.1#53(127.0.1.1) in 6343 ms com. 172800 IN NS e.gtld-servers.net. com. 172800 IN NS h.gtld-servers.net. com. 172800 IN NS d.gtld-servers.net. com. 172800 IN NS g.gtld-servers.net. com. 172800 IN NS c.gtld-servers.net. com. 172800 IN NS f.gtld-servers.net. com. 172800 IN NS j.gtld-servers.net. com. 172800 IN NS m.gtld-servers.net. com. 172800 IN NS a.gtld-servers.net. com. 172800 IN NS l.gtld-servers.net. com. 172800 IN NS i.gtld-servers.net. com. 172800 IN NS b.gtld-servers.net. com. 172800 IN NS k.gtld-servers.net. com. 86400 IN DS 30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766 com. 86400 IN RRSIG DS 8 1 86400 20131226000000 20131218230000 59085 . Y+htFwr11OK/gLaTkhlrzWSxf9mmFcXe1tXtuAtp2dRPzxcpTUULzzZo FjW2gfwGkTz/iTMp9tgkEz5g+3l5FulL5ScAhhhof615jH0iaSJu2fnb Ag2sn9w2KPii4eFREUbZ4VtU5OVOritEq7l4PnFoTjvaa+t3e8K/Lrnr udE= ;; Received 738 bytes from 220.127.116.11#53(18.104.22.168) in 10748 ms sanfoundry.com. 172800 IN NS ns1.mcqworld.com. sanfoundry.com. 172800 IN NS ns2.mcqworld.com. CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q5NFFJS5FUB0F2DNA098SBN0O663V NS SOA RRSIG DNSKEY NSEC3PARAM CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20131224054042 20131217043042 22625 com. SurvkR3vDjZP0cqltFX89tsYg127kb0bpInZaiB8HqlcV7GHQ/s6n9NO j45gJSOA4/i4SvdrYoyfa5WfQvH21Uew+ELQy5Pvzezg4uQDfjiZS8P1 feN0vZpOJaYe4bcMh+qV0zdqzmNPuJPzhswOwnMdbsAk0mZuqA1XkaPB etg= 0FM3L4FMEEBC87K8SFBLQBDASKE1OR3D.com. 86400 IN NSEC3 1 1 0 - 0FM6ACUCKFUE5RD0G1DPG1DN3ATVRRE4 NS DS RRSIG 0FM3L4FMEEBC87K8SFBLQBDASKE1OR3D.com. 86400 IN RRSIG NSEC3 8 2 86400 20131225051905 20131218040905 22625 com. y4pLl9HS4/GPgj0suNiOnqUU4j49BkOju0MIXw3WqcArCZSDW5e2yfRO G82DdP+LmP/kq7D8LANN7lIdK3Pe62BqeZDY/p/Nwr9+ilvHHH9pAlr+ MfTwVzgk+BTFHjzK95JcOZWIAnOXGlNfqv1sIdNUSAknO/V7/0EJmm5z dIA= ;; Received 605 bytes from 22.214.171.124#53(126.96.36.199) in 2255 ms sanfoundry.com. 14400 IN A 188.8.131.52 sanfoundry.com. 86400 IN NS ns2.mcqworld.com. sanfoundry.com. 86400 IN NS ns1.mcqworld.com. ;; Received 136 bytes from 184.108.40.206#53(220.127.116.11) in 529 ms
2. Get Only Short Answer using +short
$ dig +short google.com 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206
3. Display All Records using +noall
$ dig +noall +answer google.com google.com. 5 IN A 220.127.116.11 google.com. 5 IN A 18.104.22.168 google.com. 5 IN A 22.214.171.124 google.com. 5 IN A 126.96.36.199 google.com. 5 IN A 188.8.131.52 google.com. 5 IN A 184.108.40.206 google.com. 5 IN A 220.127.116.11 google.com. 5 IN A 18.104.22.168 google.com. 5 IN A 22.214.171.124 google.com. 5 IN A 126.96.36.199 google.com. 5 IN A 188.8.131.52
4. Reverse IP Lookup using -x option
$ dig -x 184.108.40.206 +short bh-7.webhostbox.net.
5. Find Domain SOA Record using +nssearch query
$ dig +nssearch amazon.in SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 220.127.116.11 in 89 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 18.104.22.168 in 90 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 22.214.171.124 in 92 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 126.96.36.199 in 96 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 188.8.131.52 in 101 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 184.108.40.206 in 110 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 220.127.116.11 in 538 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 18.104.22.168 in 538 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 22.214.171.124 in 540 ms. SOA dns-external-master.amazon.com. root.amazon.com. 2008040362 600 900 604800 900 from server 126.96.36.199 in 541 ms.
6. Find Out TTL Value Using dig
$ dig +nocmd +noall +answer a google.com google.com. 5 IN A 188.8.131.52 google.com. 5 IN A 184.108.40.206 google.com. 5 IN A 220.127.116.11 google.com. 5 IN A 18.104.22.168 google.com. 5 IN A 22.214.171.124 google.com. 5 IN A 126.96.36.199 google.com. 5 IN A 188.8.131.52 google.com. 5 IN A 184.108.40.206 google.com. 5 IN A 220.127.116.11 google.com. 5 IN A 18.104.22.168 google.com. 5 IN A 22.214.171.124
7. Queries may be directed to designated DNS servers for specific records; in this example, MX records:
$ dig MX wikimedia.org @ns0.wikimedia.org ; <> DiG 9.9.2-P1 <> MX wikimedia.org @ns0.wikimedia.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44383 ;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 3, ADDITIONAL: 8 ;; WARNING: recursion requested but not available ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 1280 ;; QUESTION SECTION: ;wikimedia.org. IN MX ;; ANSWER SECTION: wikimedia.org. 3600 IN MX 10 mchenry.wikimedia.org. wikimedia.org. 3600 IN MX 50 lists.wikimedia.org. ;; AUTHORITY SECTION: wikimedia.org. 86400 IN NS ns0.wikimedia.org. wikimedia.org. 86400 IN NS ns1.wikimedia.org. wikimedia.org. 86400 IN NS ns2.wikimedia.org. ;; ADDITIONAL SECTION: mchenry.wikimedia.org. 3600 IN A 126.96.36.199 mchenry.wikimedia.org. 3600 IN AAAA 2620:0:860:2:208:80:152:186 lists.wikimedia.org. 3600 IN A 188.8.131.52 lists.wikimedia.org. 3600 IN AAAA 2620:0:861:1::2 ns0.wikimedia.org. 3600 IN A 184.108.40.206 ns1.wikimedia.org. 3600 IN A 220.127.116.11 ns2.wikimedia.org. 3600 IN A 18.104.22.168 ;; Query time: 340 msec ;; SERVER: 22.214.171.124#53(126.96.36.199) ;; WHEN: Thu Dec 19 09:39:45 2013 ;; MSG SIZE rcvd: 278
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