EIGRP load balencing question

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Jun 17th, 2009
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Dear All


For a particular destination EIGRP is doing load balenncing over two links.


In a routing table it will have only one best route to the destination, then how it will loadbalence over the other link or how


does it will understand the secondary link




regd

Adhitya

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Giuseppe Larosa Wed, 06/17/2009 - 04:35
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Hello Adhitya,

the load balancing method depends from the switching mode used.

The default with CEF is flow based that is based on an exor of IP SA, IP DA and a seed hash.


EIGRP can perform weighted load balancing if:

the secondary route satisfies the feasibility condition:

Reported metric < Feasible distance (=current best metric to destination on local node)

and

Metric on secondary path < variance * FD


router eigrp xx

variance m


if the ratio is 4 80% of traffic will go via primary path and 20% via secondary path


Hope to help

Giuseppe


adhityakarthik Wed, 06/17/2009 - 04:43
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Hi


Thanks very much for the reply,


i am not clear about the explanation, could you please tell me in breif and also i am doing equal cost load balencing over two link



regd

Adhiyta

Paolo Bevilacqua Wed, 06/17/2009 - 04:55
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If you see only one route in table, your configuration is not correct, metrics are not the sames, etc.

So, check it.

John Blakley Wed, 06/17/2009 - 06:31
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By default, EIGRP will load balance over two links with the same cost, so you will see two routes to the same destination in your routing table. If you're only seeing one route, but you know you have two that you want to use, you'll need to configure unequal cost load balancing using the variance command under the eigrp process like Giuseppe suggests.


To see if you have another path that you can use for this destination, use the "sh ip eigrp topology" command to see your feasible successors. If you have a feasible successor in the table that goes to the same destination as the successor (the route in the routing table), then you can use the variance command to tell eigrp to use this destination as well.


HTH,

John

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