Why RIP Doesnt Support Discontiguous Networks

A discontiguous network is comprised of a major network separated by another major network. In Figure 2-7, network 131.108.0.0 is separated by a subnet of network 137.99.0.0; here, 131.108.0.0 is a discontiguous network.

Figure 2-7. An Example of a Discontiguous Network

Figure 2-7. An Example of a Discontiguous Network

RIP is a classful protocol. Whenever RIP advertises a network across a different major network boundary, RIP summarizes the advertised network at the major network boundary. In Figure 2-7, when Router 1 sends an update containing 131.108.5.0 to Router 2 across 137.99.88.0, it converts 131.108.5.0/24 into 131.108.0.0/16. This process is called autosummarization.

Router 1 takes the following steps before sending an update to Router 2:

1. Is 131.108.5.0/24 part of the same major network as 137.99.88.0/24, which is the subnet assigned to the interface that's sourcing the update?

2. No. Router 1 summarizes 131.108.5.0/24 and advertises the route 131.108.0.0/16.

The debug ip rip command output on Router 1 shows the update sent by Router 1, as demonstrated in Example 2-4.

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