Redundancy, Load Balancing and Gateways of Last Resort

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Apr 18th, 2002
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Compared to other questions, mine seems a bit "juvenile," but here goes anyway.I have two 1720 routers connected to each other by two Point-to-Point T1s. I'll call them router 'A' and router 'B'. Router 'C' is a cheap-o DSL router (soon to be a new T1 to the 'net). So, the network looks something like this:

LAN----B======A----LAN----C----INTERNET

Router B:

s0, 172.16.1.2/24

f0, 172.16.3.1/24

Router A:

s0, 172.16.1.1/24

f0, 192.168.1.100/24


Router 'B' sends all packets not on it's network to Router 'A.' Router 'A' has NAT translating the incoming packets (172.16.3.x) dynamically to 192.168.1.101-105. Access to the internet is through the DSL Router 'C' (192.168.1.1). I know that there is a problem with the 172.16.x.x/24 addresses because of the routing when I try to get the second T1 running (s1). How can I get both T1s to work? I want load balancing AND redundancy (one fails, the other stays). How would I do that?

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cantoron Thu, 04/18/2002 - 17:14
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I don't think that is a problem. It works OK for me. What is your problem?

trob Thu, 04/18/2002 - 18:57
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All you need to do is set up static routes that are dublicated for both T1s. I would point them to the IP address of the far-end interface rather than out the local interface. If a T1 drops and the far-end IP is unreachable, the router will not forward traffic across that T1. If the static directs traffic out of an interface but the local interface stays up (statics across a LAN) the setup will drop every other packet. The same will work for your default routes.

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