Basic EIGRP Question.

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Apr 10th, 2007
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I would like to achieve load balancing (using variance and CEF) over 4 EIGRP routers interconnected in squares by two connection each, one Fast Interface (used as a WAN) and the other ATM PVC as proper WAN. Two routers (in the Data center) connect a one LAN segment and the remotes connect different IP segments (they are stub) on their Ethernet port.

Now, my candidate routes already have the right routes on the topology table... But, before to apply the variance command I would like to make sure, that the neighbor will not send back the incoming traffic for same interface that they have in common. Let?s say it is making like a ?pseudo loop?. I read about split-horizon but I am not so clear to me... So, it seems that I need some help.


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Overall Rating: 2.3 (3 ratings)
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sundar.palaniappan Tue, 04/10/2007 - 09:58
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I hope I understood your setup correctly. Let us be clear. Split Horizon will prevent the router from sending routing updates out the same interface through which the route was learnt. It doesn't have anything to do with the user traffic itself.


It's very hard to say for sure whether your setup would cause any routing loop or issues without testing. If you can you should definitely lab this up and test before implementing it in production.If you are unable to test this in the lab my guess is using the variance command in your setup will very likely work fine. Based on my experience I can tell you EIGRP is good at convergence and can quickly detect any loops and clear them in a network setup like yours.


HTH


Sundar

haroon.shaikh Tue, 04/10/2007 - 18:37
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I too believe like Sundar that EIGRP is pretty good when comes to ideifyig & preventing loops, so it shouldnt be a problem though. But its worth testing the scenario beforehand...



I would also recommend using Cisco variance for load balancing over multiple Links. You can load balance in two ways: balanced or variable. In balanced, the load will be shared equally among all the links regardless the bandwidth and latency of the links. If you try variable, the load will be shared proportinal to the link's bandwidth and latency.


You might need to look into how you are going to configure variance. You also need to look into what value of variance should you use to make sure all the links are used for load balancing.



* Please rate if it helps...

Richard Burts Tue, 04/10/2007 - 18:43
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One thing to bear in mind when planning to do unequal metric load sharing with variance in EIGRP is that the alternate link must qualify as a feasible successor before variance can put the alternate route into the routing table. It is not clear to me in the original post whether the alternate link will qualify as a feasible successor.


HTH


Rick

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