Kevin Dorrell, CCIE #20765

11 Feb 2008

Static neighbors

Filed under: EIGRP, IP Routing Protocols, OSPF, RIP — dorreke @ 03:52

I’ve just realised I didn’t publish yesterday’s posting.  I’m still getting used to this blogging lark, and I must have clicked “Save” instead of “Publish”.  Anyways, it’s there now.

I’ve got a 3 a.m. bout of insomnia, so I’ve just done some experiments with the routing protocols and static neighbors.  Each protocol behaves differently.  I am too tired to write up the experiment fully, but here are the conclusions:

RIP: When you configure a static neighbor, RIP continues to multicast on the network as well as sending unicasts to the neighbor.  If you configure passive-interface, the unicasts can penetrate the wall, but the multicasts are blocked.

 EIGRP: When you configure a static neighbor, EIGRP stops sending multicasts on the network, replacing them with the unicast.  If you configure passive-interface, it blocks the unicast as well.  Moreover, you cannot mix static and multicast between two neighbors; that is, you cannot configure a static neighbor on one side and the neighbor still sending multicast. They just don’t form the adjacency.

OSPF does not allow static neighbors except in non-broadcast networks, i.e. NBMA or P2MP-NB.  In that case, the multicasts are switched off anyway.  passive-interface will block the unicasts as well.  If you have a broadcast network, the only thing you can use the neighbor command for is to modify the cost for that neighbor.

Now I’m going back to bed.

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2 Comments »

  1. sir! i completely appreciate your effort and concern,and thanks for all you provided the information.i have one question and feel ur the right person solve my problem.

    i have connected to routers cisco 2800 with cross over cable and with loop back interface configured in both router,here am trying to configure neighbor command in ospf, to form an adejecent but network type show broadcast,but in result it doesn’t form neighbor ship,here i want to know what am doing is it possible or not.

    pls suggest me.

    Regards
    Mohammed Aqeel
    aqeel_engg@yahoo.com

    Comment by Mohammed Aqeel — 13 Sep 2011 @ 11:55

    • Hi Mohammed, good to hear from you.

      The first thing to check is are the interfaces up on each router, and can each router ping the other? To form the static neighbor relationship, each router needs to be able to see its neighbor on their common network. Could you post your configuration please?

      Comment by dorreke — 13 Sep 2011 @ 19:38


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