Gotcha's With OSPF Neighborship

Even Jeff Doyle tells me that I should do a little blogging with OSPF. What's a networker to do with that kind of backing? ;-) And a few others expressed some interest as well - in understanding LSAs better, in multi-area designs, in deciphering some of the show commands, and in some of the oddball cases.

When prepping for a Cisco exam that covers OSPF - which is several of them - you need be ready to notice whether a pair of routers that share the same layer 2 network (same VLAN, same FR PVC, same pt-pt link...) can become neighbors. Once the two routers are neighbors, they can exchange LSAs (or not), depending on other factors. But as the learning theorists would say, becoming neighbors is necessary but not sufficient for routers to use OSPF to learn routes.

The problem is that if you know how to learn how to configure OSPF correctly, you avoid the issues that prevent OSPF neighborships. But for Cisco exams, you need to be ready to analyze existing config problems in some questions. There are items that must match between two routers, and just as important, items that appear to impact neighborship but do not.

So, if you haven't looked at my last post, and want to give it a shot before looking at the list of things that prevent OSPF neighborship, then go here now. When you're ready, go to page 2 of today's post for the list and the explanation of that part of my last post.

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