What is OSPF area design and types?
Answer
OSPF uses hierarchical area design to scale large networks. The backbone is Area 0 — all other areas must connect directly or virtually to it. Regular areas contain internal routers, receive full routing information. Stub area — does not accept external LSAs (routes redistributed into OSPF from other protocols); uses a default route instead — reduces LSDB size. Totally Stubby area (Cisco) — more restrictive; does not accept inter-area or external LSAs, uses only default route. NSSA (Not-So-Stubby Area) — like a stub area but allows limited redistribution of external routes via Type 7 LSAs (converted to Type 5 at ABR). Router types: Internal Router (all interfaces in one area), ABR (Area Border Router) (connects multiple areas), ASBR (Autonomous System Boundary Router) (redistributes routes from/to other routing domains). Good area design minimizes LSA flooding, reduces LSDB size, and limits SPF recalculations to specific areas.