EIGRP load balancing over unequal-cost paths

Previous post covered about load balancing over equal-cost paths. This post will explain how to load balance traffics over UNequal-cost paths.
In the case there is only one route is installed into routing table, other feasible successor routes are kept in topology table and will be refered when successor route failed. To enable load sharing over unequal-cost paths, it requires the feasible successor route is installed into routing table. A value called VARIANCE is configured to achieve this goal.
Variance is a number in range 1 to 128, where 1 is default means load balancing over equal-cost paths. Variance will be multiplied by current best metric (successor's FD) and compare with feasible successor's FD to decide whether it is useful or not. The comparison is:

If feasible successor's FD < successor's FD * variance = route will be installed into routing table.

 In this figure, R1-R4-R5 is feasible successor route for R1 to reach 1.1.1.0/24.
Feasible successor's FD is entire metric calculated from R1-1.1.1.0/24, it means 27+7+12=46
Successor's FD is: 10+5+6=21.
With variance value is 3, route R1-R4-R5 will be installed into routing table because it satisfies the condition.

For demonstration, the bandwidth in R1's s0/0 is changed to 700. Now, R1 only uses s0/1 to forward traffic to 5.5.5.0/24

R1#show ip route | section 5.5.5
D       5.5.5.0 [90/2323456] via 2.2.2.2, 00:00:04, Serial0/1

 In topology table of R1, it still keeps route via R2 to reach 5.5.5.0/24 with higher metric:

R1#show ip eig to 5.5.5.0/24
...
  2.2.2.2 (Serial0/1), from 2.2.2.2, Send flag is 0x0
      Composite metric is (2323456/409600), Route is Internal
      Vector metric:
        Minimum bandwidth is 1544 Kbit
       ...
  1.1.1.2 (Serial0/0), from 1.1.1.2, Send flag is 0x0
      Composite metric is (4322560/409600), Route is Internal
      Vector metric:
        Minimum bandwidth is 700 Kbit
       ...

To use unequal-cost load balancing over these routes, go to eigrp process and configure variance value is 2:

R1(config)#router eigrp 10
R1(config-router)#variance 2

  Now, both 2 routes are appeared in routing table:

R1#show ip route eig | section 5.5.5
     3.0.0.0/24 is subnetted, 1 subnets
D       5.5.5.0 [90/2323456] via 2.2.2.2, 00:01:08, Serial0/1
                [90/4322560] via 1.1.1.2, 00:01:08, Serial0/0

 R1#show ip route 5.5.5.5
Routing entry for 5.5.5.0/24
  Known via "eigrp 10", distance 90, metric 2323456, type internal
  Redistributing via eigrp 10
  Last update from 1.1.1.2 on Serial0/0, 00:02:17 ago
  Routing Descriptor Blocks:
    2.2.2.2, from 2.2.2.2, 00:02:17 ago, via Serial0/1
      Route metric is 2323456, traffic share count is 80
      Total delay is 26000 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2
  * 1.1.1.2, from 1.1.1.2, 00:02:17 ago, via Serial0/0
      Route metric is 4322560, traffic share count is 43
      Total delay is 26000 microseconds, minimum bandwidth is 700 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2