simple routing frustration
I'm on a fresh fedora 12 install; I'm trying to do what seems like should be a simple, uncomplicated task. Just set up routing between two interfaces. No address translation, no filtering. But its giving me problems. All the instructions that I find seem to want to tell me how to set up NAT.
Seems like I can do iptables -F to all the tables in sight, tell ip route to how to forward traffic as explicitly as I like, write "1" to /proc/sys/net/ipv4/ip_forward as often as I want, and the linux kernel still does not want to forward packets from one interface to another.
I can send and recieve packets to and from the router to either network, no problem. I can see packets from each network arrive on its interface, but it never makes it to the other interface: linux simply doesn't want to pass it along.
If I turn on masquerading in iptables - poof! - I get splendid forwarding. But then I'm doing address translation. I just want routing, not address translation. Just like a simple router would do. How do I get the kernel to just pass along the packets, just as my ip route commands tell it to do? I must be missing something - probably something simple. What am I still missing?
At first I tried this out in a VM, and figured it must be something to do with limitations around virtual network interfaces. But now I'm on bare hardware, and having exactly the same problem. Is it something about using a PAE kernel on an old pentium 4? Shouldn't just writing a one to the ip_forward file turn on forwarding? Maybe forwarding sans address translation is just a networking no-no?