When OSPF Becomes a Distance Vector Protocol

A while ago I've read an interesting post where Jeff Doyle, while describing his new-hire interview process, mentioned that inter-area OSPF is actually a distance vector routing protocol. At the time I found the argument interesting, but a bit academic.

A few months later, I've experienced interesting routing flaps in one of my lab setups. A detailed investigation revealed that they were caused by Area Border Routers redistributing inter-area information back into the area from which it originated, effectively creating a temporary routing black hole. You can find the details, in-depth explanation as well as workaround solutions in my february IP Corner article When OSPF Becomes a Distance Vector Protocol.

3 comments:

  1. Ivan

    If a sub interface is created between abr1 and abr2 then the problem can be supercedes.


    regards
    shivlu

    ReplyDelete
  2. No, the physical connectivity has nothing to do with this behavior. As long as there is some connectivity between routers in the same area, they share the same topology database and get the same SPF results.

    ReplyDelete
  3. i belive that when LSA 3 inters in an area at this time OSPF becomes Distance vector protocol.

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.