Interview Questions and Answers

OSPF supports different area types, including backbone area (Area 0), regular areas, stub areas, totally stubby areas, and not-so-stubby areas (NSSA).

OSPF uses the Dijkstra algorithm to calculate the shortest path tree, and it avoids routing loops by using the concept of a designated router (DR) on multi-access networks.

The LSDB contains information about the network's topology, represented as link-state advertisements (LSAs). Routers use this database to calculate the SPF tree.

OSPF areas are subdivisions of an OSPF autonomous system. An OSPF autonomous system is a collection of OSPF areas connected by a backbone area (Area 0).

OSPF allows for load balancing across equal-cost paths by installing multiple routes in the routing table.

OSPF metric is cost, which is inversely proportional to bandwidth. The formula is cost = 10^8 / bandwidth (in bps).

On multi-access networks, OSPF routers elect a Designated Router (DR) and a Backup Designated Router (BDR) to reduce OSPF routing traffic.

The LSAge timer in OSPF is used to age out LSAs from the LSDB. If an LSA's age exceeds its maximum age, it is considered expired and removed from the LSDB.

NSSA is an OSPF area type that allows injection of external routes while still maintaining some stub area characteristics.

OSPF selects paths based on the OSPF metric (cost). Lower cost paths are preferred. If costs are equal, the router considers other tie-breaker criteria.

Type 3 LSAs are used to advertise summarized routes from one area to another. They are generated by the Area Border Router (ABR).

Type 5 LSAs represent external routes injected into OSPF. They are generated by Autonomous System Boundary Routers (ASBRs).

Route summarization in OSPF involves aggregating multiple routes into a single summarized route, reducing the size of the routing table.

OSPF routers can be designated as internal routers, area border routers (ABRs), autonomous system boundary routers (ASBRs), or backbone routers.

In OSPF stub areas, routers do not receive external routes, reducing the LSDB size. The area relies on a default route for external destinations.