What are stub networks and why to use them?
A stub network is a term describing a computer network part of a large whole that will typically send much or all of its non-local traffic out via a single path. Stub networks are usually only aware of a default route to non-local destinations or are presented with significantly less routing information. As a practical analogy, think of an island which is connected to the rest of the world through a bridge and no other path is available either through air or sea. Continuing this analogy, the island might have more than one physical bridge to the mainland, but the set of bridges still represents only one logical path.
In the network below there is four routers, three end-user computers, one stub area, one totally stubby area, one not so stubby area, and one transit area. In real world deployments a network could have dozens or hundreds of routers, devices, or areas depending on the scale of the network. We will configure OSPF to distribute routing information as needed and configure the stub networks accordingly. Stub areas and not so stubby areas should be part of any route distributions whereas totally stub areas should not.
Verify the configuration
Now that the configuration is finished lets verify our OSPF deployment. Using the show ip ospf neighbor, show ip route, and show ip ospf virtual-links commands on R3 you can verify the remote routers to which your router has formed an adjacency and verify the expected routes are being advertised. Use the ping command to verify connectivity. As designed OSPF is distributing routing information for all networks except for area 4.
