Link-state routing protocol

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Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols.^[1] Examples of link-state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS).^[2]

The link-state protocol is performed by every switching node in the network (i.e., nodes which are prepared to forward packets; in the Internet, these are called routers).^[3] The basic concept of link-state routing is every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes.^[4] Each node then independently calculates the next best logical path from it to every possible destination in the network.^[5] Each collection of best paths will then form each node's routing table.^[6]

This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors, in a link-state protocol the only information passed between nodes is connectivity related.^[7] Link-state algorithms are sometimes characterized informally as each router, "telling the world about its neighbors."^[8]