The OSPF default mysteries

A while ago I wanted to combine the blog posts I've written about the default routes in OSPF into a single wiki article. As I started to investigate the various options you have to generate default routing in OSPF (including stub areas and not-so-stubby areas), the text quickly became too long and resulted in July IP Corner article "The OSPF default mysteries".

4 comments:

  1. It's always very interesting to ready your IPConer articles.
    Its so comprehensive.
    It's pity that these articles appeared only monthly :)

    ReplyDelete
  2. A brilliant review of a subject which is rarely found discussed in its entirety. Nicely done!

    ReplyDelete
  3. this line: The default route is originated only when a major network is matched (tested in IOS release 12.2SRC). You cannot originate a default route based on the presence of a subnet or a supernet.


    Can i not match on a network in my BGP table, to tell if BGP is up (and working)?

    i tried this:

    + ip access-list standard GOOGLE
    + permit 72.14.192.0
    + !
    + route-map GOOGLE permit 10
    + match ip address GOOGLE
    + !
    + default-information originate always metric 10 route-map GOOGLE

    and OSPF won't default-originate (though of course that network is in the table (twice!)).

    ReplyDelete
  4. As I wrote (and you quoted): The default route is originated only when a major network is matched. 72.14.192.0/24 is not a major network, 72.0.0.0/8 is.

    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.