I have a Linux box setup with 2 NICs to provide routing over 2 segment of networks using local ip. Segment A : 10.0.0.0 / 255.0.0.0 Segment B : 192.168.0.0 / 255.255.255.0 Linux box : eth0 / Segment A / 10.0.0.2 eth1 / Segment B / 192.168.0.1 I have an ISDN router on Segment B with the IP address 192.168.0.2. Hosts in Segment A is suppose to go thru the Linux box for Internet access. I plan to use the Linux box to do packet filtering and to act as a web content caching / blocking using Squid and SquidGuard. I have manage to get everything up and running. Problem, the only way I can get hosts in Segment A to access the Internet is when I turn on masquerading on the Linux box. My intention, Linux box to provide routing between Segment A & B without NAT, let the ISDN router handle the NAT. Is it possible?