Hi: My network is like this: A(IP:192.168.0.2) B(IP: 192.168.0.1)(IP:192.168.1.2) C(IP:192.168.1.1) (netmask:255.255.255.0) 255.255.255.0 255.255.255.0 255.255.255.0 (gw: 192.168.0.1) gw : 192.168.1.1 B is a machine with 2 network cards . At first I enable the /proc/sys/net/ipv4/ip_forward and set the default gw 192.168.1.1. Now, A ping B is ok and B ping C is ok. But when A ping C the network is unreachable. I don't know why. Please help me. Best wishes. Thank you. cheng