3

Is correct to say that the value inserted in the variance command, lets say the value of "2" on a route that has a cost of, lets say "100", will unequally load balance all routes up to a cost of 200 ?

regards

2

Is correct to say that the value inserted in the variance command, lets say the value of "2" on a route that has a cost of, lets say "100", will unequally load balance all routes up to a cost of 200 ?

No. The variance command doesn't change the feasibility condition; it changes the minimum metric allowed. Any paths must still meet the feasibility condition before they are considered for balancing with the variance command.

In other words, a path must have a feasible successor in order for EIGRP to consider sending traffic over that path. See the portion I have highlighted in the document below.

How Does Unequal Cost Path Load Balancing (Variance) Work in IGRP and EIGRP?

Network Diagram

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Variance

This section provides an example. In the network diagram, 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 path E-C-A with a metric of 20 because 20 is better than 30 and 45. In order 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 configuration increases the minimum metric to 40 (2 * 20 = 40). EIGRP includes all routes that have a metric of less than or equal to 40 and satisfy the feasibility condition. In the configuration in this section, EIGRP now uses two paths to get to Network X, E-C-A and E-B-A, because both paths have a metric of 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 the minimum metric of 40, because of the variance configuration. 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 is not selected for load balancing because Router D is not a feasible successor.

Note: For more information on variance, refer to Troubleshooting EIGRP Variance Command.

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