Dig
DIG, short for Domain Information Groper ) is a command line tool used to query DNS servers. it is much more advanced than nslookup. it is useful for verifying and troubleshooting DNS problems, as well as performing more advanced queries such a DNS zone transfer.
Usage
Dig has many command-line arguments, but the most basic usage is just this:
$ dig www.blackhatacademy.org ; <<>> DiG 9.7.3 <<>> www.blackhatacademy.org ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18813 ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 1 ;; QUESTION SECTION: ;www.blackhatacademy.org. IN A ;; ANSWER SECTION: www.blackhatacademy.org. 300 IN A 199.27.135.55 www.blackhatacademy.org. 300 IN A 173.245.61.144 ;; AUTHORITY SECTION: blackhatacademy.org. 86400 IN NS vera.ns.cloudflare.com. blackhatacademy.org. 86400 IN NS ed.ns.cloudflare.com. ;; ADDITIONAL SECTION: vera.ns.cloudflare.com. 85741 IN A 173.245.58.147 ;; Query time: 99 msec ;; SERVER: 91.227.204.227#53(91.227.204.227) ;; WHEN: Sat May 5 10:20:51 2012 ;; MSG SIZE rcvd: 142
This query shows information about the domains' A, the nameservers, and the TTL (Time To Live) of said records.
Dig will use the nameserver specified in /etc/resolv.conf by default, but the @ argument can be used to specify a different one:
$dig www.blackhatacademy.org @google-public-dns-a.google.com ; <<>> DiG 9.7.3 <<>> www.blackhatacademy.org @google-public-dns-a.google.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49676 ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;www.blackhatacademy.org. IN A ;; ANSWER SECTION: www.blackhatacademy.org. 300 IN A 173.245.61.144 www.blackhatacademy.org. 300 IN A 199.27.135.55 ;; Query time: 59 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Sun May 6 09:24:38 2012 ;; MSG SIZE rcvd: 73
$dig www.blackhatacademy.org +short 199.27.135.55 173.245.61.144
Dig can also be used to query other types of records, eg. MX, TXT, AAAA, NS, SRV by just specifying the record type after the domain.
$ dig google.com MX ; <<>> DiG 9.7.3 <<>> google.com MX ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42491 ;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 4, ADDITIONAL: 9 ;; QUESTION SECTION: ;google.com. IN MX ;; ANSWER SECTION: google.com. 600 IN MX 20 alt1.aspmx.l.google.com. google.com. 600 IN MX 30 alt2.aspmx.l.google.com. google.com. 600 IN MX 40 alt3.aspmx.l.google.com. google.com. 600 IN MX 50 alt4.aspmx.l.google.com. google.com. 600 IN MX 10 aspmx.l.google.com.
$ dig google.com TXT ; <<>> DiG 9.7.3 <<>> google.com TXT ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59863 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4 ;; QUESTION SECTION: ;google.com. IN TXT ;; ANSWER SECTION: google.com. 3600 IN TXT "v=spf1 include:_netblocks.google.com ip4:216.73.93.70/31 ip4:216.73.93.72/31 ~all"
$dig ipv6.google.com AAAA +short ipv6.l.google.com. 2a00:1450:4016:801::1014
Additional commands
- +nocomments – Turn off the comment lines
- +noauthority – Turn off the authority section
- +noadditional – Turn off the additional section
- +noall - Turn off all sections
- +nostats – Turn off the stats section
- +noanswer – Turn off the answer section
- +trace - Trace the nameservers the queries are going to
- +answer - Turn on the answer section
- -x - perform a reverse lookup
- -axfr - perform a DNS zone transfer. Note this is commonly disables by nameservers due to security reasons
.digrc
A file can be created in the users' home directory called .digrc to store default commands, which will automatically be used with each query
$ cat ~/.digrc +noall +answer
And now each query will only output the answer section unless specified otherwise.
$ dig www.blackhatacademy.org www.blackhatacademy.org. 300 IN A 173.245.61.144 www.blackhatacademy.org. 300 IN A 199.27.135.55
