Internal vs External EIGRP

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Aug 24th, 2007
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What makes a route show up as an external eigrp route vs an internal eigrp route other than the obivious; distribution from another routing protocol or another AS? What triggers the external flag?

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mohammedmahmoud Fri, 08/24/2007 - 08:36
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External routes are routes learned via redistribution (either from another routing protocol or another AS), and i don't think that there exits another method to trigger the external flag.


Mohammed Mahmoud.

Joseph W. Doherty Fri, 08/24/2007 - 09:30
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Possibility a "circular" answer, but anything the routing protocol considers "external" to its inner workings probably is tagged external. By inner workings, I have in mind having knowledge of the topology and in conjunction some cost metric for that topology.

Something "external" often is information provided to a routing protocol that it couldn't calculate. Your example of redistribution meets this test.

Although you asked about EIGRP, OSPF is a more interesting example because it not only has different external types, but can even tag inter area routes different from "normal" intra area routes.

sundar.palaniappan Fri, 08/24/2007 - 10:13
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""distribution from another routing protocol or another AS? What triggers the external flag?""

Both. Redistribution from another AS and another protocol/process would cause the route to show up as an External EIGRP route.



mpannill Mon, 08/27/2007 - 05:41
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Thanks everyone but I actually figured out what I was missing shortly after I posted this question. I was looking at a couple of route table entries that were showing up as external eigrp routes even though they were in the same AS. I completely missed the "redistribute connected" on one of the routers which explained the external flag.




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