OSPF routing part V - network types

Running OSPF over frame relay is a core topic when it comes to the CCIE R & S lab. In my experience when there is full reachability at L2 over the frame relay cloud the choice of OSPF network type is wide. For example OSPF broadcast and point-to-multipont network types can be made to work with the right configuration.

However care needs to be taken when L2 reachability is not a full mesh. For example in a hub and spoke frame-relay topology where the spokes do NOT have complete frame-relay map statements to all the other spokes. In this instance the network type BROADCAST will NOT do, as full reachability at L2 is a prerequisite.

With such a topology either point-to-point or a point-to-multipoint must be selected as the OSPF network type. OSPF then understands there may not be full reachability at L2. It caters for this and will ensure traffic goes via the hub to reach the other spokes.