Hierarchical OSPF
Two-level hierarchy: local area, backbone.
- Link-state advertisements only in area
- each nodes has detailed area topology; only know direction (shortest path) to nets in other areas.
Area border routers: “summarize” distances to nets in own area, advertise to other Area Border routers.
Backbone routers: run OSPF routing limited to backbone.
Boundary routers: connect to other ASs.