Routing Problem Internet | | DSL Router with NAT Enabled 192.168.93.2/24 | | | | 192.168.93.1/24 (eth1) | Linux Multihomed Router -- 10.0.0.25/8 (eth0) ------------------10.0.0.1 (host) | | 192.168.10.2/24 (eth2) | | | | 192.168.10.49 (host) The linux is running Centos 4.2. I have 3 ethernet cards, eth1 (davicom Semiconductor, Inc 21x4x DEC -Tulip Compatible), eth0 (VIA Technologies, Ic VT6105 Rhine III) Eth2 (intel Corporation 82547Gi Gigabit Ethernet Controller) I don't have any rules of iptables applied to the kernel. the content of sysctl.conf is below: # Kernel sysctl configuration file for Red Hat Linux # # For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and # sysctl.conf(5) for more details. # Controls IP packet forwarding net.ipv4.ip_forward = 1 # Controls source route verification net.ipv4.conf.default.rp_filter = 0 # Do not accept source routing net.ipv4.conf.default.accept_source_route = 0 # Controls the System Request debugging functionality of the kernel kernel.sysrq = 0 # Controls whether core dumps will append the PID to the core filename. # Useful for debugging multi-threaded applications. kernel.core_uses_pid = 1 The problem is that forwarding is enabled but when I try to probe connectivity from a host in the 10.0.0.0 net , eg 10.0.0.1 making an echo request to a host in 192.168.10.0 net , eg 192.168.10.49 the icmp packets arrive to the linux box (interface eth0) but don't traverset it. After I iniate an echo request from 192.168.10.49 to 10.0.0.1, the packets iniatated in 10.0.0.0 net starts to traverse the router magically. It seems that It needs a packet from the 192.168.10.0 to start working. I would appreciate any idea. Thanks in advance. Javier Toledano