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OSPF overload configuration

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  • 1.  OSPF overload configuration

    Posted 06-03-2021 13:38
    I have the following diagram

    I tried to configure overload on vMX5 to force outbound traffic via vMX2 from vMX8. Can I do this ?

    I did some tests and did not work. not sure whether caused by my poor image or something I missed.

    thanks !!


  • 2.  RE: OSPF overload configuration

    Posted 06-03-2021 14:15
    I did more tests and noticed it might be caused by NSSA.  After I removed NSSA,  it works.

    Anyone can coach me why overload does not work for NSSA.


  • 3.  RE: OSPF overload configuration
    Best Answer

     
    Posted 06-04-2021 11:08

    Hi, 

    OSPF overload causes LSAs advertised by the router to set its metrics to 65535 (max metric).
    In the NSSA it would depend on NSSA configuration whether summaries  or default-lsa is generated by ABR and sent into NSSA.

    If summaries are allowed, then max-metric is set.

    Example:

    Summary  1.1.1.1          1.1.1.5          0x80000002   126  0x20 0x41f0  28
      mask 255.255.255.255
      Topology default (ID 0) -> Metric: 65535
      Aging timer 00:57:54
      Installed 00:02:05 ago, expires in 00:57:54, sent 00:02:03 ago
      Last changed 00:02:05 ago, Change count: 2


    If no-summaries and only default-lsa is sent into NSSA generated by ABR, then overload max-metric will not be set, as the default-metric is a static value.
    On vmx5/8, the metrics can be verified:

    show ospf database area 2 advertising-router <router-id-vmx5> extensive


    Cheers,



    ------------------------------
    Ashvin
    ------------------------------



  • 4.  RE: OSPF overload configuration

    Posted 06-04-2021 11:15
    thanks so much for your insights !