From: Ryan Morris (ryan@egate.net)
Date: Wed Mar 05 2008 - 16:15:47 ARST
Here's a scenario I've run into in real life:
We have a branch office with two WAN connections, primary and backup.
Traffic will only take the backup link if the primary is not available.
We run EIGRP between these routers and our data centre routers. I'm
planning to summarise the routes coming out of these branch routers in
order to simplify my routing table. Per best practice, there is a
loopback address in each of the branch routers that is in the netblock
for that office.
Inside the branch office, there is a group of core switches made up of two
3550s. Each 3550 connects to one of the WAN routers, and has an EIGRP
relationship with the other 3550 and the connected router.
So if the primary WAN link or the primary router fails, no problem.
Traffic routes to the backup.
Problem: if the connection between the primary router and the 3550 fails
(or, let's say the switch dies), that router will continue to advertise
the summary because of the loopback, and because it has a better
metric than the backup, traffic will not fail over to the backup.
Any ideas on how to solve this? i.e. a feature that shuts down an
interface or explicitly stops advertising a route if another interface
fails? Or is the the simple answer (take the loopback off the primary
router) the only way to keep this from happening?
Input appreciated!
Ryan Morris
CCIE #18953
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