IE6, reboot to resolve DNS

I’m sorry, know I’ve seen this answer somewhere before. I’ve had some clients (all on the same local ISP) have trouble where they can browse the net for a while, then suddenly they cannot resolve DNS. They can ping IP addresses, even browse sites by IP address, but the only way to solve the problem is to reboot. Then they can browse again for a while.

I know the answer has something to do with the ISP blocking certain ports. You can go to a certain number of sites before you start hitting those ports…..something like that. I’m sure someone knows what I’m talking about. Is the answer to just flush DNS? I don’t remember.

Thanks!