Content

| 5.5 |  | Troubleshooting IGRP |
| 5.5.4 |  | Maximum paths |

By default, for load balancing purposes, Cisco routers support only four equal paths. The command maximum-path can be used for up to six equal-cost paths. If the command is not configured properly, it can cause problems.

Figure shows a network setup with multiple equal-cost paths from router R1 to the 131.108.2.0/24 network.

Figure shows the routing table entry for router R1, where only one route is being installed in the routing table.

Debugs and Verification
Figure shows the output of debug ip igrp transactions command on router R1, revealing that R1 is receiving two equal-cost path routes. However, the routing table showed that only one route is being installed.

Figure shows the current configuration for router R1. The maximum-path command has been configured with the value of 1, which prevents IGRP from installing more than one path in the routing table. By default, the maximum-path is set to four.

If the command maximum-path 1 is used, it will only allow one path to the destination even though more than one path exists. The maximum-path 1 command should only be used when load balancing is not desired.

Solution
By default, Cisco IOS Software allows up to four equal-cost routes to be installed into the routing table. This can be increased up to six routes if configured properly. Figure shows the configuration that installs six equal-cost route paths in the routing table.

This example makes more sense when there are more than four paths and only four are being installed in the routing table. Because four equal-cost routes is the default, the maximum-paths command can be configured to accommodate a fifth or possibly sixth route.