OSPF Discontiguous Area 0
Refer to the following OSPF network topology:
In this topology, Area 0 is discontiguous. In such a scenario:
- Routes will be exchanged correctly between Area 1 and each Area 0
- Thus, routing will correctly take place between Area 1 and both components of Area 0
- Any routes learned by Area 1 from one Area 0 will not be learned by the other Area 0
- 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.