iptables firewall with multiple external interfaces routing probl em

[Jeff Adam <jadam () seark edu>]

The problem that I have run into is that only the first dhcp interface to
activate will 
talk to the internet. 

I place my DMZ behind eth2 and my LAN behind eth1 and eth0 then forward port
25 
on eth2 to my exchange server on my DMZ and 80 to my web server on my DMZ

redhat 9 iptables fw
eth0  external connected to cable dhcp reserve x.x.x.12
eth1  external connected to cable dhcp reserve x.x.x.45
eth2  external connected to cable dhcp reserve x.x.x.55
eth3  internal connected to LAN                         172.x.x.x
eth4  internal connected to DMZ                       192.x.x.x
eth5  inactive                                                  not used

The problem is that when the system boots only the LAN has internet
connectivity
behind eth0.  I can deactivate eth0, eth1 and eth2, then activate only eth2,
and only 
the DMZ has connectivity.  The internet is able to connect back to the
servers 
in my DMZ as planned. I then activate eth0 and eth1, and still only the DMZ
has 
connectivity. I deactivate eth0-2 and only the interface that activates
first appears 
to work. I am at a loss as to what I am missing.

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