Conditional OSPF default route origination based on classless IP prefixes

Almost two years ago I wrote the OSPF default mysteries IP Corner article in which I’ve described (among numerous other details) the caveats of conditional OSPF default route origination; it requires an IP access list that can only match classful networks.

Later someone sent me a message stating that you can match classless IP prefixes with an ip prefix-list ... and it took me well over a year to find the time (and mental energy) to lab the scenario and document the results.

The sender was correct: you can originate OSPF default route based on presence of a classless IP prefix in the IP routing table; you’ll find details in the Conditional OSPF default route origination based on classless IP prefixes article in the CT3 wiki.

I’ve also fixed the OSPF default routes article in the wiki to include the summaries of all relevant articles in the CT3 wiki (previously it only contained a link to the IP corner article).

2 comments:

  1. Ian; thanks for the update. Isn't the config of the X2- router in the wiki supposed to have 'remote-as 65101' as the BGP debug show in the path-list No it lists remote-as 65000?
    Keep up the good work.

    ReplyDelete
  2. Ivan Pepelnjak17 June, 2010 11:26

    You're absolutely correct - somehow I've managed to remove the EBGP neighbor when cleaning the configuration file :'( Fixed.

    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.