Resolving an IP-Forwarding Problem

I'm trying to set up a Windows 2000 Professional machine as a router between two class C networks (LanA and LanB). I've installed two NICs on the Win2K Pro machine, which is in LanB, and set the appropriate default gateway, IP addresses, and subnet masks. I can ping the router machine from both networks but can't ping through it from LanA to hosts on LanB or from LanB to hosts on LanA. I haven't defined any static routes on any machine. Do you have any idea how I can resolve this problem?

First, verify that you've enabled IP routing on the Win2K Pro system (for information about this process, see the Windows Client UPDATE article "Enable IP Forwarding on a Win2K Pro System," http://www.winnetmag.com, InstantDoc ID 9691). Next, verify that only one of the two NICs that you installed on the router system has a default gateway. Also, verify that you've configured the appropriate default gateway on all the systems on both subnets. To simplify the configuration and make the gateway address easier to remember, I also recommend that you make the default gateway on both subnets the first address in the subnet (i.e., x.x.x.1).