If you can get on your router and look at the line stats, check your downstream FEC or CRC errors. If you have interleaving enabled, you're more likely to have FEC errors. If you have a lot (several tens of thousands) I'd either resync or reboot your router. If you don't, and you're a long way from the exchange, check your CRC errors. If you're looking at several thousand, same applies. A large number of accumulated errors can cause problems with DNS resolution and general browsing. After a recent rain storm, I had somewhere in the region of 42 million downstream FEC errors! FEC theoretically shouldn't matter, they've already been corrected by the time they reach you. In practice, they can be an utter bastard.