[CentOS] Forwarding connections/packets across interfaces

Tue Apr 18 00:35:19 UTC 2006
Alan Sparks <asparks at doublesparks.net>

Have a inter-interface routing issue, hoping someone can either throw a 
clue or point me where I can get one.  This is on a CentOS 3.7 system.

Have interfaces eth0 and eth1.  eth0 is connected to internal network, 
eth1 to separate distinct network.  The default route on the box is set 
to the roter address on the eth1 network.  I have static routes defined 
to send local network traffic to eth0 and eth0's router.

I have a mail server (and a test program as well) that binds to an 
address on eth1, and tries to connect to an address on eth0's network.  
Connections just time out.  I've tested connections where I did not bind 
to a specific interface and I can make the connection.

I've set rp_filter=0, and ip_forward=1 for all interfaces, and still 
cannot get a connection from eth1's address to something off of eth0's 
networks.  Firewalls are disabled on the host.

Is there additional voodoo that needs to be set to allow traffic to 
cross from one interface to the other?

Thanks in advance for any advice or pointers.  I hope I've made the 
problem clear enough...

Alan Sparks, UNIX/Linux Systems Integration and Administration
<asparks at doublesparks.net>