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| 5.4 |  | Troubleshooting RIP |
| 5.4.4 |  | Discontiguous networks |

When a major network is separated by another major network, this is called a discontiguous network. Figure shows an example of a discontiguous network.

Debugs and Verification
Figure shows the configuration for routers R1 and R2. RIP, with the default of Version 1, is enabled on the Ethernet interfaces of R1 and R2 with the correct network statements.

Figure shows the debug ip rip command output for routers R1 and R2. The debugs show that both routers are sending to each other the summarized major network address for 137.99.0.0, instead of their specific network addresses. As a result, both routers will ignore the less specific 137.99.0.0 update because they are already connected to this major network.

Solution
RIP is not installing the route 137.99.0.0 in the routing table because RIP v1 does not support discontiguous subnets. Several solutions to this problem exist. Figure shows that a quick solution is to configure each router with a static route to the specific 137.99.0.0 subnet on the other router. Since RIP v1 does not include the subnet information in its routing updates, configuring the static routes is a “patch” to fix this problem. This may be necessary if the routers in question can only run RIP v1.

Another solution is to change the address on the link between routers R1 and R2 to be part of the 137.99.0.0 network. In other words, assign another subnet on this link, which is part of 137.99.0.0.

Figure shows a better solution, to enable the classless routing version of RIP v2 with no auto-summary configured on both routers. The no auto-summary command will disable auto-summarization of RIP v2 routes when crossing a major network boundary. It is important to disable the auto-summarization or the same unreachability problem will continue to exist. With no auto-summary, the specific subnet information is also included in these updates. Figure shows the routing table of R2 after using this solution.

Another solution is to replace the classful RIP v1 routing protocol with a classless routing protocol, such as OSPF, EIGRP, or IS-IS.