There may be occasions when you wish to query a DNS server directly. I often do it before changing DNS servers for a domain; I’ll setup the new records on the new DNS servers, and then query them directly to ensure they are returning the correct records.
I recommend that anyone running DNS services for any domain looks into these commands – they’re very useful, especially when you’re making changes.
dig has a feature which allows you to specify a name server along with the record you want to query.
For example, one of the DNS servers for droptips.com is “ns.123-reg.co.uk”. We can query this server directly, for the www record by doing the following:
$ dig droptips.com @ns.123-reg.co.uk
You’ll get some output with a section titled Answer Section:
;; ANSWER SECTION: droptips.com. 86400 IN A 89.238.134.5
This details the result (89.238.134.5) and also the TTL for the record (in seconds). The TTL is important, as this is how long caching DNS servers should cache the result for – in this case, 86400 seconds which is 1 day. Using this command to find out a TTL value for a particular record is also quite useful, especially if you’re investigating DNS cache issues.
You can also do the same to check other records such as MX records, by simpling adding the record type to the command. For example, to get the MX records ns1.google.com is reporting for google.co.uk:
$ dig MX google.co.uk @ns1.google.com
… with the results:
;; ANSWER SECTION: google.co.uk. 10800 IN MX 10 google.com.s9a2.psmtp.com. google.co.uk. 10800 IN MX 10 google.com.s9b1.psmtp.com. google.co.uk. 10800 IN MX 10 google.com.s9b2.psmtp.com. google.co.uk. 10800 IN MX 10 google.com.s9a1.psmtp.com.
You can see in this instance, that the TTL is 10800 seconds which is 3 hours, and all MX records have the same priority level of 10.