Default Route failover for EIGRP

[ahilton]

I'm looking for a way to have EIGRP fail over to a secondary default route in case it's primary fails. I don't want to load balance. Say I have two core routers (7200) each with their own ISP gateway, and dependant 2nd tier routers below each. If Router A is connected to say Sprint, and Router B is connected to AT&T, they each have a default route to 0.0.0.0 pointing to each ISP. If Router A's connection to Sprint fails, how can I have EIGRP configured to fail over and direct 0.0.0.0 traffic to Router B for access via AT&T?

[deilert]

If the default route is static you can redistribute static , on each router , then the default static will be preferred on each router and the redistributed route will be the backup route , a statically configured default route will have an admin distance of either 0 or 1 when the route is redistributed it will hace an admin dist of 170. You can verify that you have the backup route by doing a 'sh ip eigrp top 0.0.0.0 0.0.0.0' , you will see both routes

[vcjones]

You don't say whether you are running BGP with each ISP to support a single set of IP addresses, if each ISP's users are using a set of IP addresses associated with each ISP, or if the users are getting out by having the routers do NAT/PAT.

The solution is slightly different in each case, but basically, you want to redistribute the default route as learned by each of your two outside routers into EIGRP (whether from BGP or from statics) with a higher cost than the local default route. You then also need to ensure that when an ISP link fails, the default route associated with that link also goes away so the backup route can be seen.

If the routers are doing NAT/PAT, you will also need to ensure that the traffic is NAT/PATed to the correct range for the ISP actually being used.

There is discussion of all the options, and the pitfalls with each, in Chapter 8 of my book "High Availability Networking with Cisco." The example configurations in the book are also on my web site.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com