I use a service at home to unlock region-locked web content, particularly internet video. As I’ve mentioned previously, I run a Windows 2008 R2 server on our home network which is our domain controller, and (as a result) our DNS server too.
The service I use for unlocking content requires that you set the DNS server on the network to the values it specifies. That’s not viable for me because of course the client machines need to use the internal DNS server in order to be able to find the domain controller, but no problem - the windows server VM can act as the DNS server just fine, handle requests relating to the internal network domain itself, and forward everything else off using the forwarders I specify (which come right from my content unlocking service).
This worked great until a few weeks ago, and then it suddenly stopped working.
I don’t know why and I’m not quite technical enough to fully grasp the details, but the problem was EDNS (whatever that is). The blog post I’ve linked above talks about it more depth, but the bottom line for me is that once I turned EDNS off everything worked fine.