Forcing traffic out the same interface on a dual homed server (without using routes) ?

[Felix <fmontes@gmail.com>]

Hi all,

If i have 2 interfaces on a linux server, say eth0 and eth1, and 
a) default gateway is eth0 = production
b) there is a complex network on eth1 = administration
c) i can't have routing entries for the administration network
(dont ask why, its an OSI layer 9 problem (the political layer))

Can iptables restrict traffic that came in through eth1/administration to 
only go out through eth1?

I think what i'm trying to do is bypass the routing decision if somehow it 
was known on which interface the connection initiated. And even if iptables 
could manage to send the traffic out the same interface, would it just be 
dropped on the local subnet? how would it be sent to the default gateway on 
that subnet?

Your enlightening comments will be appreciated.

Regards,
-Felix