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Link-state routing protocol

Link-state routing protocol definition

A link-state routing protocol allows routers to map the network by sharing details about the state of their directly connected links.

See also: interior gateway protocol, OSPF, IS-IS, routing table

History of link-state routing protocols

Link-state protocols were developed to overcome the limitations of distance-vector protocols. In the 1980s, larger and more complex networks needed more efficient routing methods. The first standardized link-state protocol was the Open Shortest Path First (OSPF) protocol, introduced in 1989.

How a link-state routing protocol works

  1. 1.Initialization. When powered on, a link-state router discovers nearby routers and establishes two-way communication.
  2. 2.Link-state advertisement (LSA). After discovery, the router creates a packet about the state of its links, known as a link-state advertisement (LSA).
  3. 3.LSA flooding. The LSA is then sent to all other routers in the network. Each router updates its database and shares the LSA further.
  4. 4.Database construction. Based on the received LSAs, each router builds a complete network database.
  5. 5.Shortest path calculation. Using algorithms like Dijkstra's, routers find the shortest path to each destination.

Examples of link-state routing protocols

  • Open Shortest Path First (OSPF). A widely used link-state protocol standardized by the IETF and suitable for large enterprise networks.
  • Intermediate System to Intermediate System (IS-IS). Originally developed for the ISO's Connectionless Network Protocol (CLNP), it was later adapted for IP networks.
  • NetWare Link Services Protocol (NLSP). A protocol developed by Novell for its Internetwork Packet Exchange (IPX) protocol.