Lesson 38: OSPF Fundamentals

Open Shortest Path First (OSPF) is a widely used, non-proprietary Link-State routing protocol. It is highly scalable and efficient.

OSPF Operation

1. Neighbor Discovery: Routers use multicast Hellos (224.0.0.5) to find adjacent OSPF routers.
2. Exchanging LSAs (Link-State Advertisements): Routers share information about their connected links and status.
3. Building the LSDB (Link-State Database): All routers in the same area have an identical copy of the LSDB.
4. Running the SPF Algorithm: Each router uses the LSDB to calculate the Shortest Path Tree (SPT) to all destination networks.

OSPF Areas

OSPF uses a hierarchical, two-layer structure called areas to improve efficiency and scalability.

• Area 0 (Backbone Area): All other areas must connect to Area 0.
• Standard Areas: Any area other than Area 0.

Router Types:

• Internal Router: All interfaces are in the same area.
• Area Border Router (ABR): Connects one or more areas to the backbone (Area 0).