[LARTC] Route 2 Internet connections on a local LAN

[Joel Kleppinger <jkleppinger@earthlink.net>]

I know it is poor form to ask a question after just joining a mailing list, 
but I searched around for an archive and couldn't find out.  I pray you'll 
forgive my brashness.

What I am trying to do is have 2 internet interfaces properly routing on 
the same box using the 2.4 kernel.  I have a cable modem and a DSL modem 
(eth2) running into a single server which provides a few services to the 
outside world, including HTTP.  This server also is forwarding the cable 
modem NIC (eth1) to the internal LAN (eth0) using SNAT.  If I switch the 
default route and enable iptables to forward the DSL modem to LAN, then 
that works fine as well.  So all 3 interfaces are effectively working, but 
only 2 of the Internet interfaces at a time.  I've tried making both Net 
interfaces the default route, but it only routes the interface that was 
last made default.

I want to make it so that someone can access the machine from either 
Internet IP (both static) so I can use the DSL interface (eth2) as a server 
or route certain ports coming in on eth2 it specifically to another server 
behind the routing machine.  I would like this without interrupting the 
current cable modem SNAT connection.

I have discussed this notion with a lot of people, and it seems that no one 
really knows how to do this.  It seems like it really shouldn't be that 
hard to put services out over specific interfaces.  So I ask here.  If 
anyone can give me any sort of guidance, direction, even a smile, I would 
be IMMENSELY grateful.

Thank you,

Joel Kleppinger


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