I cannot find any documentation that explains these lines. Please could somebody explain what they are and what causes them. We have a router that seems to be losing its routes occasionally and goes onto ISDN.
Suppose you have a router with two routing protocols running. If both routing protocols know about a given destination, they will both attempt to install a route to that destination in the routing table. Only one of them will install the route, however, based on the administrative distances of the routes. The route that loses (because its administrative distance is lower) is called the "backup route."
When a route is removed from the routing table, every routing protocol that has registered a backup route for that destination is called, in turn, so they each attempt to install the route in the routing table. This is the call you are seeing in your debugs.
Now, it sounds like your ISDN is dialing because you're losing routes--you're next step needs to be to figure out why you're losing those routes. It sounds like they aren't EIGRP routes, since EIGRP is being called to install the backup routes (?), though I could be wrong there (it all depends on your network). What I would do is figure out where I normally get those routes, and find out why I'm losing them.
Is there a neighbor adjacency failing? Is the link flapping? There are a ton of reasons you could be losing these routes in the first place.
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