Nope, you don't need any routes at all. There's no need for the router to know the path to every single prefix explicitly. With two default routes, you just set the higher priority one to the preferred ISP. The router will use that one exclusively, unless something happens to the interface.
Here's what happens on a failure of your preferred ISP. Since you're advertising your own prefixes through both interfaces, the advertisements through the preferred interface will be withdrawn and the rest of the world will start using the path through the backup ISP. So your incoming traffic will switch to the backup. For outgoing traffic, the router will notice that the preferred default route no longer points to an "up" interface, and so it will withdraw it from the routing table. The lower priority default route will take over. We've used this technique in the past for some of our rural POPs that have a T1 primary link and a 56K backup link. (Now we just use the default route injection feature of OSPF.) Now if you want to load balance, that's another story! :-) Even with that, though, there are some tricks you can do so that you carry a minimum of routes. Oh, there is one assumption in all this, and that is that the same router connects to both ISPs. Even that can be worked around, though, using the OSPF default route injection feature I mentioned above. -- Bruce Robertson, President/CEO +1-775-348-7299 Great Basin Internet Services, Inc. fax: +1-775-348-9412 http://www.greatbasin.net _______________________________________________ RLUG mailing list [EMAIL PROTECTED] http://www.rlug.org/mailman/listinfo/rlug
