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configure eigrp variance

Posted on 2011-02-11
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Last Modified: 2012-05-11
My question is, if I configure eigrp variance to share out my traffic across multiple links what is the default traffic sharing ? I know you can use commands like traffic-sharing balanced/min however I want to know what the default is without configuring anything else.

Thanks
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Question by:tech2010
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Expert Comment

by:srico_gisd
ID: 34874017
If you do not configure a shaping metric there is an implied 1 metric applied which is equal distribution among links. This is for Cisco so....
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Expert Comment

by:gmooney7
ID: 34874180
variance (EIGRP)

To control load balancing in an Enhanced Interior Gateway Routing Protocol (EIGRP) based internetwork, use the variance command in router configuration mode. To reset the variance to the default value, use the no form of this command.

variance multiplier

no variance
Syntax Description

multiplier
      

Metric value used for load balancing. It can be a value from 1 to 128. The default is 1, which means equal-cost load balancing.

Defaults

1 (equal-cost load balancing)
Command Modes

Router configuration
Command History
Release
      
Modification

10.0
      

This command was introduced.

Usage Guidelines

Setting a variance value lets the Cisco IOS software determine the feasibility of a potential route. A route is feasible if the next router in the path is closer to the destination than the current router and if the metric for the entire path is within the variance. Only paths that are feasible can be used for load balancing and included in the routing table.

If the following two conditions are met, the route is deemed feasible and can be added to the routing table:

•The local best metric must be greater than the metric learned from the next router.

•The multiplier times the local best metric for the destination must be greater than or equal to the metric through the next router.
Examples

The following example sets a variance value of 4:

router eigrp 1

 variance 4

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Author Comment

by:tech2010
ID: 34897405
srico_gisd are you sure about this ? because i am not seeing that behaviour. i am using 12.4 and its doing unequal load balancing on unequal paths which i believe is proportionate.

gmooney7 - i am afraid you did not get my question i know what variance is and how to configure that, anyways thanks for your effort.
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Expert Comment

by:gmooney7
ID: 34897711
Sorry about that.

Have a look at this article
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

Look at the section regarding traffic sharing.
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Author Comment

by:tech2010
ID: 34901173
thanks mate but what is the default without configuring traffic-share command...
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Author Comment

by:tech2010
ID: 34901211
i have seen that document by my question is what is the default behaviour.
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Accepted Solution

by:
gmooney7 earned 500 total points
ID: 34902905
The default is to balance the traffic proportionately  based on a ratio of the (variance * minimum cost) / cost. You then round down to the nearest integer.  It uses this number as the traffic share count.

So, say you have 3 routes with the least cost route having a ratio of 3, second one 2, and last one with a cost of 1.  Traffic will be sent 3 packets to the first route, 2 to the second, 1 to the last, and recycle back to the first route at 3 packets.  This is the way I understand it.

Take a look at this.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#loadbalancing
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