From: Melwani, Manoj J (melwanim@citigroup.com)
Date: Fri Sep 09 2005 - 11:58:10 GMT-3
See if this helps. I have also attached a pdf.
EIGRP Load Balancing
Every routing protocol supports equal cost path load balancing. In addition to that, IGRP and EIGRP also support unequal cost path load balancing. Use the variance command to instruct the router to include routes with a metric less than n times the minimum metric route for that destination, where n is the number specified by the variance command. Use the Command Lookup Tool ( registered customers only) to find information on the variance command. The variable n can take a value between 1 and 128, with the default being 1, which means equal cost load balancing. Traffic is also distributed among the links with unequal costs, proportionately, with respect to the metric.
Note: If a path is not a feasible successor, then the path is not used in load balancing. Refer to the Feasible Distance, Reported Distance, and Feasible Successor section of Enhanced Interior Gateway Routing Protocol for more information.
Network Diagram
------20---------Router B--------10-------- (Metric 30)
Router E-----10---------- Router C-------10--------- Router A (Metric 20) NETWORK X
-----20--------- Router D--------25------- (Metric 45)
Variance
Let us look at an example. In the network diagram above, there are three ways to get to Network X:
E-B-A with a metric of 30
E-C-A with a metric of 20
E-D-A with a metric of 45
Router E chooses the second path above, E-C-A with a metric of 20, because 20 is better than 30 and 45. To instruct EIGRP to select the path E-B-A as well, configure variance with a multiplier of 2:
router eigrp 1
network x.x.x.x
variance 2
This increases the minimum metric to 40 (2 * 20 = 40). EIGRP includes all routes that have a metric less than 40 and satisfy the feasibility condition. In the above configuration, EIGRP now uses two paths to get to Network X, E-C-A and E-B-A, because both paths have a metric under 40. EIGRP does not use path E-D-A because that path has a metric of 45, which is not less than the value of minimum metric of 40, due to the variance configured. Also, the reported distance of neighbor D is 25, which is greater than the feasible distance (FD) of 20 through C. This means that even if variance is set to 3, the E-D-A path will not be selected for load balancing since Router D is not a feasible successor.
Try this link http://www.cisco.com/warp/public/103/19.html#intro
Regards,
Manoj J. Melwani
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Anis Faruqui
Sent: Friday, September 09, 2005 9:44 AM
To: Cisco certification
Subject: Variance in EIGRP
Hi Group,
Dear all please shade some more light on the Use of Variance Command in
EIGRP Domain ,How to calculate it in a simple and easiest way ?
Need your help..
Anis :)..
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