Hi,
The quickest way to kill a LAN is to use the ISP's DNS, especially at load. I would setup your own internal DNS.

>Thanks for your reply,
>
>We're not using an internal DNS, we are using DNS server provided by our ISP. I am currently working on this issue thru our firewall and ISA SERVER. Thanks anyway, your reply was very helpful to understand this issue. I also think dns lookup is not enough to slow a network down. I have stopped live streaming, file downloads, IM and such thru our firewall and now Internet is ok and fast :).
>
>Thanks,
>
>Jim.