Content

| 5.4 |  | Troubleshooting RIP |
| 5.4.2 |  | Mismatched authentication key |

One of the options in RIP v2 is that RIP v2 updates can be authenticated for increased security. When authentication is used, a password must be configured on both sides. This password is called the authentication key. If this key does not match the key on the other side, the RIP v2 updates will be ignored on both sides.

This example shows two routers running RIP between each other.

Debugs and Verification
Figure shows the configurations of routers R1 and R2. In this configuration, a different RIP authentication key is configured on R1 and R2. The R2 Ethernet interface is configured with the key cisco1, whereas R1 is configured with the key cisco. These two keys do not match, so they ignore each other’s updates, and the routes will not be installed in the routing table.

Figure shows the output from the debug ip rip command on router R2 that indicates that R2 is receiving a RIP packet that has invalid authentication. This means that the authentication key between sender and receiver does not match.

Solution
When using authentication in RIP, make sure that the sender and receiver are configured with the same authentication key. Sometimes, adding a space at the end of the key can cause the invalid authentication problems because a space will be taken as a literal key entry. As a result, this causes a problem that cannot be corrected just by looking at the configurations.

Debugs will show that there is a problem with the authentication key. To solve this problem, configure the same keys on both sender and receiver, or retype the authentication key, making sure that no space is being added at the end.

Figure shows the new configuration to correct this problem. The authentication key is reconfigured on router R2 to match the key on router R1.

Figure shows the routing table of R2 after the configuration change.