A question arises from the preceding discussion: How does a RIP process interpret the subnet of a major
network if it has no interfaces attached to that network? Without an interface on the class A, B, or C
network of the destination, the router has no way of knowing the correct subnet mask to use and therefore
no way of correctly identifying the subnet.
The solution is simple: If a router has no direct attachments to the network, then it needs only a single
route entry pointing toward a router that is directly attached.
NOTE
Boundary routers perform route summarization, also known as subnet hiding.