OSPF Overview
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OSPF stands for Open Shortest Path First. It is a link state routing protocol for IP networks.
OSPF does not use a transport protocol such as UDP or TCP. It encapsulates its data directly in IP packets with protocol number 89.
OSPF uses Dijkstra algorithm and falls into the group of interior gateway protocols, operating within a single autonomous system.
OSPFV2 supports IPv4 which was defined in RFC 2328 (1998), OSPFV3 supports IPv6 which was defined in RFC 2740 (1999). OSPF supports the Classless Inter-Domain Routing (CIDR) addressing model.
OSPF is widely used in large enterprise networks, but less common in large service provider networks.
OSPF gathers link state information from available routers and constructs a topology map of the network. The topology is presented as a routing table for routing packets by their destination IP address.
OSPF detects changes in the topology, such as link failures, and converges on a new loop-free routing structure within seconds. It computes the shortest-path tree for each route using a method based on Dijkstra's algorithm.
OSPF divides the network into routing areas to simplify administration and optimize traffic and resource utilization.
OSPF dose not send routing information directly to other OSPF routers, It uses Link-State Advertisements (LSA) to represent any topology change. Each OSPF router will calculates it own routing information according to LSA received from other OSPF routers and inserts to routing table.