Problem IGRP Not Using Unequal Cost Path for Load Balancing Cause variance Command Is Missing or Misconfigured

To use the variance feature (unequal-cost-path load balancing), it must be configured under the router igrp command. By default, IGRP does not do unequal-cost-path load balancing. Also, when the variance factor is multiplied by the current best metric, the resulting number is compared with other available path metrics. Any available path metric that is under this resulting number will be used for unequal-path load balancing.

Figure 5-39 shows the network setup susceptible to this problem. The network 155.155.0.0/16 is known through two paths, but only one is in the routing table.

Figure 5-39. Network Setup Conducive to Load-Balancing Problems

Figure 5-39. Network Setup Conducive to Load-Balancing Problems

Figure 5-40 shows the flowchart to follow to solve this problem.

Figure 5-40. Problem-Resolution Flowchart

Figure 5-40. Problem-Resolution Flowchart

Debugs and Verification

Example 5-97 shows the routing table entry on R1 showing that R1 is using only one path to reach 155.155.0.0/16.

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