OSPF Network Types

OSPF Network Types

OSPF’s functionality is different across several different network topology types. They are mentioning below

Broadcast Multi-Access – indicates a topology where broadcast occurs.

        •   OSPF will elect DRs and BDRs.

        •   Traffic to DRs and BDRs is multicast to 224.0.0.6. Traffic from DRs and BDRs to other routers is multicast to 224.0.0.5.

        •   Neighbors do not need to be manually specified.

        •   Examples Ethernet

Point-to-Point – indicates a topology where two routers are directly connected.

        • No DRs and BDRs.

        •   All OSPF traffic is multicast to 224.0.0.5.

        •   Neighbors do not need to be manually specified.

Point-to-Multipoint – indicates a topology where one interface can connect to multiple destinations. Each connection between a source and destination is treated as a point-to-point link.

        •    OSPF will not elect DRs and BDRs.

        •   All OSPF traffic is multicast to 224.0.0.5.

        •   Neighbors do not need to be manually specified.

Non-broadcast Multi-access Network (NBMA) – indicates a topology where one interface can connect to multiple destinations; however, broadcasts cannot be sent across a NBMA network.

        •   An example would be Frame Relay.

        •   OSPF will elect DRs and BDRs.

        •   OSPF neighbors must be manually defined, thus All OSPF traffic is unicast instead of multicast. 

Remember: On non-broadcast networks, neighbors must be manually specified, as multicast Hello’s are not allowed.

Related articles

• Difference between Linkstate and distance vector protocols
• OSPF neighbors
• OSPF DR and BDR election 
• Basic Notes on OSPF (Open Shortest Path First)