I am trying to make a comparison test between two different Packet Filters implementations and I want to use the following testbed :only two machines with 2 interface cards each
1-->sender(eth0 machine;forwarding is disabled for this machine;Ubuntu9.10
2-->and gateway(wm0; wm1;forwarding is enabled

The problem is I don't manage to obtain a correct configuration:when I try to ping from sender interface to receiver interface through the gateway
I can see with wireshark the requests on the receiver interface
,but this interface is not replying in turn.
ping -I eth0 or ping -I eth1 have the same behaviour as explained up

Any information would be very useful.Thank you