Why do I get slow network throughput when I have a bad DNS server?

"If you have bad DNS the initial request will be slow, then once the lookup is cached, your speed should be fine.

It may be a routing issue though with packets trying a wrong default gateway, I had that problem with my dual airport express' once I unplugged the one that was not connected to the net it was fine.

Start by doing a ping and a tracerouce and look at the latency and any dropped packets."