OSPF (Open Shortest Path First)

A link-state routing protocol used within large enterprise networks to find the shortest path for data packets using Dijkstra algorithm.

What is OSPF?

Open Shortest Path First (OSPF) is an interior gateway protocol (IGP) used for routing within a single autonomous system. It uses link-state routing and Dijkstra's algorithm to calculate the shortest path between network nodes.

How OSPF Works

OSPF routers discover neighbors, exchange link-state advertisements (LSAs), and build identical topological databases. Each router then runs the SPF (Shortest Path First) algorithm to calculate optimal routes to all destinations.

OSPF Areas

OSPF networks are divided into areas to improve scalability:

Backbone Area (Area 0): Central area connecting all other areas
Standard Areas: Regular routing areas
Stub Areas: Simplified routing with default routes
NSSA: Not-So-Stubby Areas for external route handling

Key Features

Fast convergence after topology changes
Support for VLSM and CIDR
Authentication for security
Hierarchical design through areas
Classless routing protocol
No hop count limitations