OK, here's my problem. I'm trying to set up a Linux box to act as a router/firewall for my dual boot WinME/Linux box and a Mac. I can ping the mac and the pc (when running linux) from the firewall (and vice versa).
The problem shows up when I boot into windows. In this case, I can't ping in either direction between the pc and the firewall. However, when I run tcpdump on the firewall and try to ping it from windows, I can see the icmp-request and icmp-reply packets going across the interface. Thus, it would appear that windows is for some reason ignoring the packets that come out of the firewall system. Does anyone know of a setting or configuration option in windows that could cause this?

It looks like Windows doesn't have the correct ip settings. It produces icmp-reply packet, the router answers to the incorrect ip, but routes it to another interface.

alpha-wolf

No, it's different. Windows can send packets out on the interface (it sends the icmp-request packet). It just doesn't see any packets coming in on that interface.

Hey,
do you run a personal firewall on the windoze? Are you shure, that the icmp-reply leaves the router the same interface wich the request came from? use tcpdump with the "-i" option.

alpha-wolf

Yes, I'm sure. I was using tcpdump -i eth2 (eth2 is the interface the windows box is on). I don't think I'm running a firewall on the windows box. Is there some setting in the network configuration that would cause windows to block incoming ports?

Hmm,
its not an incoming port. Its just the icmp reply. I just know that a personal firewall would block this. Try using tracert, then a icmp time exeeds come back maybe this arrives at your M$-Box.

alpha wolf