EIGRP next-hop processing

Update @ 2009-06-01: The exact EIGRP behavior in IOS releases 12.3 and later is described in the EIGRP next-hop processing article in the CT3 wiki.

Update @ 2009-05-30: The information in this post is incorrect, the no ip next-hop-self eigrp command changes EIGRP next hop processing.

Yap Chin Hoong sent me a detailed e-mail describing his efforts to use the Next Hop field present in EIGRP routing updates. His conclusions (that I’ve subsequently verified with a few lab tests) were disappointing: although EIGRP updates have a next hop field, it’s not used (unlike OSPF forwarding address).

When doing the tests, I’ve reused an old NBMA topology and thus started to wonder whether I hadn’t already tested the EIGRP behavior. Turns out I had … and summarized the EIGRP behavior as “EIGRP updates contain no provision for changing IP next-hop address” in the Next-hop fixup in partially-meshed NBMA networks article (In the meantime, I’ve fixed the text to reflect the reality).

This article is part of You've asked for it series.

8 comments:

  1. Conclusion from TAC on the case opened by Yap Chin Hoong is that this is considered a feature request and not a bug.

    If you want this feature, please involve your account team.

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  2. I didn't claim it was a bug; I've just documented the behavior ... it's a bit sad, though, that the "next-hop" field is in the update data but not used.

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  3. What about "no ip eigrp next-hop-self" for DMVPN?

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  4. I labed this up using ethernet ( same broadcast domain) and tried using no ip next-hop-self eigrp *AS* it didn't make any difference, when i sniffed the EIGRP update packet both times(with and without next hop self) the Next hop address = 0.0.0.0

    i thought if i made the destination network a internal eigrp route the next hop self would work so i blocked eigrp packets between the source and the destination and added the destination network to eigrp, this way the source has to learn the route from the intermediate still didn't change anything.

    i have a GNS3 DMVPN lab around somewhere, it might be worth getting that out and looking what it does to the next hop address in the eigrp update packet.

    cheers

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  5. Hi Ivan, I read the article on CT3 Wiki, seems that redistributing between EIGRP ASs work with the no ip next-hop-self eigrp command. But I still face problem when redistributing a static route into EIGRP in similar network setup. Kindly help to have a look on this. Thanks. :)

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  6. hi I am trying to do the same as the chap above redistribute a tracked route into eirgp, that i need advertised without a next hop as the next router is on the same subnet, but does not having tracking cababilites. This works in OSPF but NOT eigrp...any ideas?

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  7. people asking your about EIGRP on Ethernet and you talking about NBMA?!? =-X

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  8. Ivan Pepelnjak02 May, 2010 07:11

    It all started with DMVPN, then some people decided to lab it using Ethernet.

    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.