Dear folks, I have just subscribed because we ran into a problem that many people we asked were not able to solve. I hope that this is the right place for asking. Please bear with me if it's not. We have a latest Debian running a 2.4.24 kernel. Pretty straight forward, absolutely nothing special about it. The box is routing between two NICs (inner and outer LAN). Internal is private IP-addresses, external is a public one. We configured an overload-nat like this: iptables -A POSTROUTING -s 192.168.100.0/24 -o eth0 -j SNAT --to x.x.x.1 Nothing more. We have flushed all other queues. This has been working on many boxes we have set up. Today, we ran into the problem that *some* of the packets travelling from internal eth1 to eth0 (outside) do not get NATed although the rule is in there. Apparently these are mostly ICMP packets (like ping) but also others like UDP/53 (DNS) do not get NATed. This is really strange because we did tests like: - Reboot Linux-Router - Linux-Client (192.168.100.5) can not ping - Windows-Client (192.168.100.6) can ping - Linux-Client can suddenly ping, too. When the boxes are not able to ping, it is just because the appropriate packets don't get NATed and end up at the ISPs router since they have RFC1918 addresses in the source field. Making a long question short: why do some packets get NATed and others don't? Please tell me if you need any additional information to evaluate. This might be obvious but we did not find anything. Thanks a lot. Cheers! Sascha
