This example sets up an OSPF network at a large office. There are three areas, each with two routers. Typically OSPF areas would not be this small, and if they were the areas would be combined into one bigger area. However, the stub area services the accounting department which is very sensitive about their network and do not want any of their network information broadcast through the rest of the company. The backbone area contains the bulk of the company network devices. The regular area was established for various reasons such as hosting the company servers on a separate area with extra security.

One area is a small stub area that has no independent Internet connection, and only one connection to the backbone area. That connection between the stub area and the backbone area is only through a default route. No routes outside the stub area are advertised into that area. Another area is the backbone, which is connected to the other two areas. The third area has the Internet connection, and all traffic to and from the Internet must use that area’s connection. If that traffic comes from the stub area, then that traffic is treating the backbone like a transit area that only uses it to get to another area.

In the stub area, a subnet of computers is running the RIP routing protocol and those routes must be redistributed into the OSPF areas.

This section includes the following topics: