OSPF Point-to-Multipoint Network Type over Frame-Relay

[lagapidis (Lazarus Agapidis)]

Hello Po

At the beginning of each of these lessons, Rene explains how OSPF “perceives” the network and consequently behaves. For OSPF Point-to-Multipoint Network Type:

• There is automatic neighbor discovery so there is no need to configure OSPF neighbors manually.
• There is no need for DR/BDR elections since OSPF sees the network as a collection of point-to-point links.
• A single IP subnet is used in the topology.
• In order for this to work, frame-relay must be configured to process broadcasts, which means the configuration must use the broadcast keyword.

For OSPF Broadcast over Frame Relay, the only difference is that DR/BDR elections take place because OSPF perceives the network as a single broadcast domain, and not as a collection of individual point to point links.

@cpj_68

I tried to understand the differences but the configurations look almost similar except the declaration of ip ospf network and one with priority 0.

They are very similar. The difference is indeed that for OSPF Point-to-Multipoint Network Type, priority is set to 0 so that no DR/BDR elections take place. The ip ospf network command exists in all configurations since this is the command with which particular networks are advertised.

@cpj_68

Also, the OSPF non-broadcast VS OSPF point-to-multipoint looks similar too as both of them are required to designate the neighbors.

Non-broadcast does indeed require the neighbors to be configured, but point to multipoint does not.

For details of each OSPF network type and its characteristics and differences, take a look at this post:

OSPF Non-Broadcast Network Type over Frame-Relay

Hello Muhammad OSFP network types are a special case of OSPF implementation. They are used in order to accommodate specific technologies such as frame relay. It is for this reason that they are only described after the main topic of OSPF. In any case, the reason they exist is that technologies such as frame relay cannot support broadcast and multi access infrastructure, which are prerequisites for normal OSPF functionality. The various types of networks are used to allow OSPF to have DR and…

I hope this has been helpful!

Laz