Thank you for your responce Steve. But, all nodes on this network have the same IP network address, including Ethernet port of the router, DCs, Proxy 2, ISA, and Workstations. If I put another NIC into ISA box, it has to have another network address, isn't it? Suppose I put another network address to it, it doesn't seem that this NIC can talk to anyone on this network. It will be great if you can tell me which particular article on isaserver.org is talking about this matter. Thank you. Mark Zhang