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.
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
- Initialization. When powered on, a link-state router discovers nearby routers and establishes two-way communication.
- Link-state advertisement (LSA). After discovery, the router creates a packet about the state of its links, known as a link-state advertisement (LSA).
- LSA flooding. The LSA is then sent to all other routers in the network. Each router updates its database and shares the LSA further.
- Database construction. Based on the received LSAs, each router builds a complete network database.
- 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.