OSPF (Open Shortest Path First) is a routing protocol used by routers to determine the best path for data to travel in a network. OSPF operates on the basis of link-state routing, in which each router advertises a description of its local network connections to other routers in the network. Below are the main steps involved in OSPF:
1. Establishing Neighborship: OSPF is a classless routing protocol that establishes neighborship between the OSPF routers. Routers must be directly connected to each other in order for neighborship to be established. Once neighborship has been established, routers begin exchanging information about their connectivity.
1. Building the Link State Database: OSPF routers exchange packets called Link State Advertisements (LSAs). LSAs are used to build a database of the entire network’s topology. Routers send their LSAs to all OSPF routers within the same area, and the routers use this information to update their link-state databases.
1. Shortest Path First Computation: OSPF calculates the shortest path first (SPF) using the Dijkstra algorithm based on the link-state database. The SPF algorithm finds the shortest path to every destination network, and OSPF routers store this information in their routing table.
1. OSPF Path Selection: Once all the routers have completed SPF calculations, each router processes its routing table and selects the best path to send data to its destination based on the shortest path.
1. Network Redundancy: OSPF allows for redundant paths within the same network, which provides network redundancy in case of link failure or congestion. When a link fails or becomes congested, OSPF automatically adjusts to use an alternate path to the destination network.
Overall, OSPF provides reliable and efficient routing by allowing for network redundancy and finding the shortest path to each destination network through exchanging and processing LSAs.
