Single-Area OSPF is great for small networks, but as your topology grows, the SPF algorithm becomes computationally expensive. Multi-Area OSPF solves this by dividing the routing domain into hierarchical areas.
The Backbone (Area 0)
All non-backbone areas must connect directly to Area 0. The backbone acts as the transit area for inter-area traffic.
OSPF Router Roles
- Internal Router (IR): All interfaces are in the same area.
- Backbone Router (BR): Has at least one interface in Area 0.
- Area Border Router (ABR): Connects a regular area to the backbone. Summarization occurs here.
- Autonomous System Boundary Router (ASBR): Injects external routes (like EIGRP or static routes) into OSPF.