January 02, 2014

Lab 22: EIGRP Unequal-cost Load Balancing

Configure EIGRP on all routers. After the configuration, R1's EIGRP routing table will be like this:

R1#sh ip route eigrp
     35.0.0.0/24 is subnetted, 1 subnets
D       35.0.0.0 [90/3193856] via 12.0.0.2, 00:01:24, Serial0/0
     23.0.0.0/24 is subnetted, 1 subnets
D       23.0.0.0 [90/2681856] via 12.0.0.2, 00:01:24, Serial0/0
     56.0.0.0/24 is subnetted, 1 subnets
D       56.0.0.0 [90/2707456] via 14.0.0.4, 00:01:24, Serial0/1
     192.168.0.0/32 is subnetted, 1 subnets
D       192.168.0.1 [90/2835456] via 14.0.0.4, 00:00:14, Serial0/1
     46.0.0.0/24 is subnetted, 1 subnets
D       46.0.0.0 [90/2681856] via 14.0.0.4, 00:01:24, Serial0/1

As you see, R4 is the next-hop for 192.168.0.1/32.
We should calculate the the variance for unequal-cost load balancing. Let's check EIGRP topology table on R1:

R1#show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(14.0.0.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 12.0.0.0/24, 1 successors, FD is 2169856
        via Connected, Serial0/0
P 14.0.0.0/24, 1 successors, FD is 2169856
        via Connected, Serial0/1
P 23.0.0.0/24, 1 successors, FD is 2681856
        via 12.0.0.2 (2681856/2169856), Serial0/0
P 35.0.0.0/24, 1 successors, FD is 3193856
        via 12.0.0.2 (3193856/2681856), Serial0/0
        via 14.0.0.4 (3219456/2707456), Serial0/1
P 46.0.0.0/24, 1 successors, FD is 2681856
        via 14.0.0.4 (2681856/2169856), Serial0/1
P 56.0.0.0/24, 1 successors, FD is 2707456
        via 14.0.0.4 (2707456/2195456), Serial0/1
P 192.168.0.1/32, 1 successors, FD is 2835456
        via 14.0.0.4 (2835456/2323456), Serial0/1
        via 12.0.0.2 (3321856/2809856), Serial0/0

For 192.168.0.1/32, minimum required variance is 3321856/2835456=1.17. So we should configure the variance on R1 as 2:

router eigrp 1
 variance 2

As a result, both paths are added to R1's EIGRP routing table:

R1#show ip route eigrp
     35.0.0.0/24 is subnetted, 1 subnets
D       35.0.0.0 [90/3219456] via 14.0.0.4, 00:00:10, Serial0/1
                 [90/3193856] via 12.0.0.2, 00:00:10, Serial0/0
     23.0.0.0/24 is subnetted, 1 subnets
D       23.0.0.0 [90/2681856] via 12.0.0.2, 00:00:10, Serial0/0
     56.0.0.0/24 is subnetted, 1 subnets
D       56.0.0.0 [90/2707456] via 14.0.0.4, 00:00:10, Serial0/1
     192.168.0.0/32 is subnetted, 1 subnets
D       192.168.0.1 [90/2835456] via 14.0.0.4, 00:00:10, Serial0/1
                    [90/3321856] via 12.0.0.2, 00:00:10, Serial0/0
     46.0.0.0/24 is subnetted, 1 subnets
D       46.0.0.0 [90/2681856] via 14.0.0.4, 00:00:10, Serial0/1

Also you can observe that traffic share count for 192.168.0.1 is 48 and 41:

R1#sh ip route 192.168.0.1
Routing entry for 192.168.0.1/32
  Known via "eigrp 1", distance 90, metric 2835456, type internal
  Redistributing via eigrp 1
  Last update from 12.0.0.2 on Serial0/0, 00:02:41 ago
  Routing Descriptor Blocks:
  * 14.0.0.4, from 14.0.0.4, 00:02:41 ago, via Serial0/1
      Route metric is 2835456, traffic share count is 48
      Total delay is 46000 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 3
    12.0.0.2, from 12.0.0.2, 00:02:41 ago, via Serial0/0
      Route metric is 3321856, traffic share count is 41
      Total delay is 65000 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 3

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