OSPF Discontiguous Area 0

Refer to the following OSPF network topology:

In this topology, Area 0 is discontiguous. In such a scenario:

1. Routes will be exchanged correctly between Area 1 and each Area 0
2. Thus, routing will correctly take place between Area 1 and both components of Area 0
3. Any routes learned by Area 1 from one Area 0 will not be learned by the other Area 0
4. Thus, routing between the two Area 0s will not function at all

OSPF employs a split-horizon type rule that states that any routes learned by Area X from Area Y are not to be readvertised into Area Y.

A solution to this problem is to create a virtual link between the two discontiguous Area 0s.

OSPF where do you configure a virtual link

Links:

https://networklessons.com/ospf/how-to-configure-ospf-virtual-link

https://datatracker.ietf.org/doc/html/rfc2328#page-136