Multirouting 2 ISP with public addresses

Wayne Alday waynea at
Wed Aug 17 00:33:49 CEST 2005

List :

I have a similar setup to this gentleman:

eth0 connected with the LAN
eth1 connected with the internet across ISP1
eth2 connected with the internet acorss ISP2

Although I can find a thousand examples on how to do this with NAT, 
there doesnt seem to be anyone wanting to do it with real IP addresses, 
or not that I have found in 3 days of searching.

I read the following link :

Seems to be just what I need, except I do not wish to load balance or 
have servers avaiable everywhere, or have redundancy, but just for the 
box to do what i guess would be called source routing. My delimma is 
that living in a remote town bandwidth costs are moderate to high. I 
have a 6 meg bonded T-1 setup on a cisco 3640 router that we outgrew 
quickly. A DS-3 connection where I live would of cost nearly 15K / month 
because we live near no POP.So we put some fiber up, and needless to say 
we have 10 / mbit with the capability to turn it up as needed at a much 
cheaper cost. The problem is we are having to eat the monthly charges 
for our current bandwith and would like to utilize it for CPE. Im pretty 
sure with the research I have done that this is possible to put on our 
current linux router, but  I must be  missing a key somewhere, and I 
would like a fresh look on the problem.

Here is what I wish to do.

eth1 is connected to my 6mbit line thru the FE0/0 port on the 
eth2 is connected to the fiber transceiver to 10 mbit (
eth0 is connected to my lan. (

I have route statements in the 3640 that route ALL traffic for the 
public addresses thru a private subnet
ip route
ip route
ip route
ip route
ip route
ip route
ip route

The linux box in turn hands it off to various other parts and routers

What I would like to do is throw the following 4 Class C addresses onto 
eth2 and have them route according to what network.
For instance if I assign a CPE an Ip address in the 12.150 range, i wish 
for all that traffic to route out eth1 to the wireline
If I assign a CPE IP in the 70.158 ranges, I would like it to route out eth2

The router on the other side of the fiber net has the exact same routes 
for the 70.158 ranges as the ones on my wireline with the exception
they are routing to instead of

Ive seen suggestions on marking packets, setting up 2 routing tables, 
and others, but i have had limited success on getting this going.

Could anyone provide some thoughts or input or an example? It would be 
greatly appreciated. If I havent been descriptive enough, will provide 
more details

Thanks in advance


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