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Question on running multiple routing protocols (EIGRP, Ripv2, IGRP)

Posted on 2005-04-27
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ok, I'm running Ripv2, IGRP and EIGRP on my 3 routers (lab environment)  Each router is running all 3 of those routing protocols.  Ripv2 and EIGRP are auto-summarizing.

When I disable EIGRP's auto summary, I notice   "I's" start appearing in my routing table on some of my routers.  

I know that diabling auto-summary lets the routing protocol advertise the REAL subnet mask (instead of the summarization).

-But, why does IGRP take over some of the routes EIGRP was taking care of? Th AD of EIGRP is lower...shouldnt it ALWAYS beat out IGRP?

I'm confused on why disabling auto-summarization in EIGRP, lets another routing protocol (with a higher AD) control that route. What relation does auto-summarization have with AD?
thanks

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Question by:dissolved
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harbor235 earned 2000 total points
ID: 13877936
Remember that IGRP does not support VLSM, . IGRP will see routes only at their classful boundaries and not recognize subnetted prefixes. Eigrp auto summary will summarize routes at the classful boundary. It sounds like the EIGRP routes are being tagged as external eigrp routes which has an AD of 170 which is higher. Look at the AD of the routes youare talking about the the EIGRP routing table.

harbor235
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by:harbor235
ID: 13877964
Look in the toplogy table for info on the routes you detailed. Can you post your config? Are you redistributing? Are you using the same AS for IGRP as well as EIGRP?

harbor235
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by:dissolved
ID: 13878015
Hi harbor. I'm not redistributing. The AS for the IGRP and EIGRP are different.

So external EIGRP routes (aka summarized to classful boundary) have an AD of 170???

How do I view the EIGRP routing table? The sh ip ro command right? Thats what I have been using. I dont have access to it here at work, but will post when I get home
Thanks!
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by:harbor235
ID: 13879578
You need to look at the EIGRP topology table:

show ip eigrp topology

harbor235
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by:dissolved
ID: 13888254
harbor, what is the difference between external EIGRP routes (170 AD) and regular EIGRP routes (80 AD <--I think)
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by:dissolved
ID: 13889449
answer when you get a chance.
thanks
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by:harbor235
ID: 13894890
Internal Eigrp routes are routes that are learned from within the EIGRP routing domain (AS). External routes are those routes that have been learned fromo another routing protocol and have been injected via redistribution, and they are also routes that are in the routing table as static routes and again are injected via redistribution. One type is explicitly configured in Eigrp
the other is learned outside of EIGRP.

harbor235
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by:dissolved
ID: 13895797
u da man!
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