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Configuring a multihomed network

I have two internet circuits connected to my Cisco 3640 router – the primary is a T1 and the secondary is a DSL.

The ISP who supplied my T1 has allocated us a block of 6 usable IP’s (29-bit mask).

I am running NAT on my router and have created a static NAT to my vpn server and also to my email server.

I had my ISP created an A-name for the vpn server and MX record for the email server.

When I enable the DSL interface, I notice that outbound emails begin to pile-up in the queue. As soon as I shutdown the DSL interface, the queue empties.

Also, with the DSL interface enabled, remote users have complained that they are unable to contact the vpn server. Again, once I shutdown the DSL interface, remote users are able to connect to the vpn server.

Any idea what’s going on here? I’m sure I’m not the first network administrator to encounter this dilemma.

Also, what are my options/work-arounds?

I’m not a large enough site to justify a full class-C network or run BGP on my edge routers.

Thank you for your help!



Re: Configuring a multihomed network


Please post parts of your router configuration to clarify the problem.

For some reason traffic prefers the DSL interface, but can't find it's way back to the IP address that is advertised by the ISP of your T1.

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