Junos OS

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  • 1.  IS-IS and DIS

    Posted 10-12-2018 08:20

    Just wanted clarification on this question:


    During my certification process I had numerous questions on IS-IS and a couple were based around the requirement of a DIS if no point-to-point is configured. I don't agree with this as I have configured IS-IS as our IGP on our 4 MX routers and have NOT configured point-to-point and it works just fine. No issues at all.....


    Is point-to-point required only on level 1 systems? Or is a DIS required only on level 1 systems if point-to-point is not configured?

  • 2.  RE: IS-IS and DIS
    Best Answer

    Posted 10-12-2018 11:13
    DIS is elected only in broadcast network type irrespective of level.

    Can you share config and below outputs where you don’t see the DIS elected in broadcast network in level 2?

    show isis adj details
    show isis interface details

  • 3.  RE: IS-IS and DIS

    Posted 10-14-2018 15:14

    The test questions can be tricky in wording to trigger pulling red herring answer options provided.


    My recollection for IS-IS DIS was that they were generally around knowing one or more of these points:

    • only needed in broadcast segments with more than two nodes
    • Route flooding works differently than ospf broadcast links
    • The election process itself


  • 4.  RE: IS-IS and DIS

    Posted 10-15-2018 03:13

    Thanks for the responses guys.


    From investigation it looks like the DIS is assigned via an election on our network.


    Much appreciated.