Using Linuxconf to setup IP forwarding has a bug, or it may be in the startup scripts, if you do a # echo 1 > /proc/sys/net/ipv4/ip_forward the forwarding works .... if you reboot you loose the ip_forwarding. it could be related to /etc/rc.d/init.d/network ??
You can change the line in /etc/sysctl.conf to be 1 instead of 1.
Sorry, I meant change it from 0 to 1(Duh). Anyway, this is really a duplicate of Bug #10434.
10434 has been closed now. *** This bug has been marked as a duplicate of 10434 ***