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Variance command in EIGRP

Posted on 2011-10-18
Medium Priority
Last Modified: 2012-05-12
I wanted to know if someone could explain the variance command within Cisco and more specifically, EIGRP.

Question by:ee4itpro
1 Comment
LVL 25

Accepted Solution

Ken Boone earned 2000 total points
ID: 36990502
OK so basically the variance command gives EIGRP the ability to use multiple UNEQUAL cost paths for routing traffic.  So normally I can load balance with equal cost paths no problem.  But lets say I have a network with multiple paths between endpoints but they are not the same path.  Now lets say I still want the ability to load balance - or rather should I say load distribute across the different UNEQUAL cost paths.  I use the variance to do this.

So first of all for a route to be eligible for this it must be a feasible successor.  You will have to study a little about EIGRP to learn up on this, but basically its a router that is not as good as the primary route, but that it good take over if the primary route failed.

So lets say I have a route from point A to point B.  There are two paths I could take.  On one the metric is 100 and the other the metric is 150.  So the 100 metric is the route I choose.  If I use a variance I am saying that I will accept lesser routes as long as they are within the value of (variance X metric of main route).  If my metric is 100 and I use a variance of 2 then I will accept routes for load sharing with any other routes with a metric up to 200.  If I use a variance of 3 then 300 and so on.

In addition to this we can also use another command with this:

traffic-share balanced

This command when used with variance will all traffic to flow over both paths proportionately to the metric that each route has.

Hope this helps.

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