Although I have 4 DNS servers with 4 different providers, they all slave off a "hidden" master Amazon AWS server.
Unfortunately something has gone wrong with the AWS server - it reports on amazon as 100% ok but I can't connect to it (even after rebooting) and thus of course the DNS slaves can't talk to it either.
I've rerouted the DNS for now and all should be OK again.
Now to work out what's up with the AWS server ...
I've been having DNS issues on off yesterday all day. I use L3 as my primary and OpenDNS as secondary.
M