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Metric In EIGRP

Unanswered Question
Mar 19th, 2012
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Hello,


I am using GNS3 For a topology as in attachment. I configure EIGRP on all routers. R! and R2 has 2 link with same bandwidth (1544). R1 routing table show both path due to same metric. But when i change bandwidth (3544) on s0/1 on R1, metric of that link does not change. R1 remain show two path.


But when i Configure same topology with all fast ethernet link, the metric changes on bandwidth change of F0/0 on R1 and it show only one path after bandwidth change.

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Peter Paluch Mon, 03/19/2012 - 05:47
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Hello,


I assume you are talking about the route from R1 to R6.


Remember that EIGRP considers the lowest bandwidth along the path. The fact that you increase a link's bandwidth may not change the metric at all if there is another bottleneck on the path. In your topology, the bottleneck still remains on the R2/R6 link, and increasing the link's bandwidth on R1 will not influence it. That is most probably the reason why you don't see the total metric change.


Try, however, lowering the bandwidth on R1/R2 link under 1544. That should move the bottleneck to this link and then, you should see a change.


Best regards,

Peter

Harmeet Singh Mon, 03/19/2012 - 07:43
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Thanx Peter Sir,


U R Right.


I want to ask one more thing, What is difference between to change Bandwidth and change speed on an fast ethernet? Does they both effect on metric. Can we change speed of serial interface?

dslice Mon, 03/19/2012 - 19:25
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The speed is unknown to EIGRP unless it also changes the bandwidth value, which is reported to EIGRP. I also strongly agree with the earlier responder who stated that delay is a better attribute to change to influence path selection.


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John Blakley Mon, 03/19/2012 - 07:25
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On another note, it's best to change delay instead of bandwidth outside of a lab environment. Bandwidth statements are used in other calculations like qos and changing bandwidth could impact those types of decisions negatively.

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