Troubleshooting Routes Summarization in RIP

Route summarization refers to summarizing or reducing the number of routes in a routing table. For example, 131.108.1.0/24, 131.108.2.0/24 and 131.108.3.0/24 can be reduced to one route entry (that is, 131.108.0.0/16 or 131.108.0.0/22), the latter of which will cover only these three subnets. Route summarization (autosummarization and manual summarization, both of which are addressed in this section) is used to reduce the size of the routing table. This section discusses the most significant problem related to the route summarization ‚ the RIP-2 routing table is huge. Two of the most common causes for this are as follows :

• Autosummarization is off.

• ip summary-address is not used.

Figure 3-38 shows a network setup that could produce a large routing table.

Figure 3-38. Network Setup That Could Generate a Large Routing Table