When I was writing the zine How DNS Works earlier this year, someone asked me – why do people sometimes put a dot at the end of a domain name? //

almost every line starts with a ;;. What’s up with that? Well ; is the comment character in zone files!

So I think the reason that dig prints out its output in this weird way is so that if you wanted, you could just paste this into a zone file and have it work without any changes.

This also explains why there’s a . at the end of example.com. – zone files require a trailing dot at the end of a domain name (because otherwise they’re interpreted as being relative to the zone). So dig does too. //

There are two contexts where domain names are modified and get something else added to the end:

• in a zone file for example.com, grapefruit get translated to grapefruit.example.com
  • on my local network (with my computer configured to use the search domain lan), grapefruit gets translated to grapefruit.lan

So because domain names can actually be translated to something else in some cases, people like to put a "." at the end to communicate “THIS IS THE DOMAIN NAME, NOTHING GETS ADDED AT THE END, THIS IS THE WHOLE THING”. Because otherwise it can get confusing.

The technical term for “THIS IS THE WHOLE THING” is “fully qualified domain name” or “FQDN”. So google.com. is a fully qualified domain name, and google.com isn’t.