Duct tape. The Force. DNS.
These are the things that bind our world together. Sure, you can't see the force when you're juggling rocks while standing on your head, just like you don't pay attention to DNS 99% of the time you're browsing the web, but that doesn't mean it doesn't affect everything you do.
Misconfigured DNS has caused more, weirder problems than any other single aspect of networking I've yet encountered. Sure, it causes plain, vanilla connectivity issues when you can't resolve something, but it gets much weirder.
Misconfigured DNS causes mail to break, active directory to stop authenticating (or to even recognize that domains exist), SSH sessions to timeout instead of connect, and an entire host of other problems.
I have even had it cause password issues: the DNS that I was on pointed to a different machine, yet configured identically and with all the same identifiers, and when someone added my account to the machine she was talking to, I couldn't get access. We fought with this for a few hours before I got desperate enough to check into the IP addresses we were connecting to.
This is just a friendly reminder that DNS is everywhere, and if you're having a bizarre network issue, make sure DNS is somewhere early in your troubleshooting checklist.