Thursday, 14 June 2012

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.

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