Saturday, June 14, 2008

Book: OSPF Network Design Solutions

I am reading the 2nd edition of this book and I recommend it to anyone who wants to know more about OSPF. I skipped chapter 1 and read chapters 2 and 3 today. A lot of this stuff was review from Routing TCP/IP volume 1 and from what I read of the RFC for OSPFv2. However I did learn some new things, so here is a quick rundown of what I read or found out while labbing and reading:

·You can filter out LSAs intra area with the following commands:
ip ospf database-filter all out (interface mode)
neighbor x.x.x.x database-filter out (router ospf mode)

·The BDR is elected before the DR, then promoted to DR if there is not a current DR.

·When summary routes or external LSA's change, only a partial SPF calculation is required. Full SPF calculations are run when there is a type 1 LSA change.

·Debug the SPF calculation with the following:
debug ip ospf spf inter
debug ip ospf spf external

·Stub area flag is known as the E bit

·External Summary LSA's are not specific to an area. In other words, they are contained in their own section in the "show ip ospf database" command output.

·If forwarding address is in a type 5 LSA, then traffic is forward to the originator of the advertisement.

·LSA group pacing:
timers pacing lsa-group (router ospf mode)

There are also some real good case studies at the end of each chapter. The more I read, the more I will post.


  1. This command has few more options... Just to add to your post....

    R2(config-router)#max-metric router-lsa ?
    external-lsa Override external-lsa metric with max-metric value
    include-stub Set maximum metric for stub links in router-LSAs
    on-startup Set maximum metric temporarily after reboot
    summary-lsa Override summary-lsa metric with max-metric value

  2. this command is used with BGP integration, as BGP is more slow to converge than OSPF, the max-metric is used to wait for BGP Convergence... it's talked on CCIE v4 wendell's odom book!

  3. I have also read about OSPF, but was unaware of the term BGP, many thanks for the help as am very sure on its usage now.

    Emily from Arbre à chat design 


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