Julia Evans has a cool new web tool for experimenting with DNS. She wrote up why she created it and some of the tech behind the tool on her announcement post:
Mess With DNS gives you a real subdomain, and it’s running a real DNS server (the address is
mess-with-dns1.wizardzines.com). The interesting thing about DNS is that it’s a global system with many different computers interacting, and so I wanted people to be able to actually see that system in action.