OSPF Network Types

OSPF Network Types

Understanding OSPF Network types is bit tricky unless you don’t start from the concepts.

We have totally 5 different network types in Cisco Networks:

RFC Specific:

1.    Non-Broadcast

2.    Point to multipoint

Cisco Specific:

3.    Point to Multipoint non-broadcast

4.    Point to point

5.    Broadcast

Non-Broadcast:

·         Default Network type on Cisco routers.

·         Routers cannot discover neighbors automatically, thus manual neighbors must be configured. (it is enough if you just configure on the Hub)

·         Hellos are sent as Unicast.

·         DR/BDR elections happen.

·         Hub must be elected as DR as it has full connectivity to the spokes. And spokes cannot get elected as DR/BDR.

·         Need to set the priority to 0 on the Spoke’s interface.

·         Hello and Dead timers are 30/120

Point to Multipoint:

·         Automatic neighbor discovery happens.

·         Hellos are sent as Multicast

·         No DR/BDR elections

·         Hello and dead timers are 30/120.

Point to Multipoint Non-Broadcast:

·         Routers cannot discover neighbors automatically, thus manual neighbors must be configured. (it is enough if you just configure on the Hub)

·         Hellos are sent as Unicast.

·         No DR/BDR elections.

·         Hello and Dead timers are 30/120.

Point to point:

·         Default on point to point sub-interfaces

·         Neighbors are discovered automatically.

·         Hellos are sent as Multicast.

·         No DR/BDR elections

·         Hello and Dead timers are 10/40

Broadcast:

·         Neighbors are discovered automatically.

·         Hellos are sent as multicast

·         DR/BDR elections happen.

·         Hello and Dead timers are 10/40

I will configure all these network types in a frame-relay network and post in my subsequent posts.