Link-state routing protocols were developed to address some limitations of distance vector protocols. When running a link-state routing protocol, routers originate information about themselves (IP addresses), their connected links (number and type of links), and the state of each those links (up/down). The information is forwarded from router to router in the network. Each router makes a copy of the information and does not change it. Each router maintains a map of the network and independently calculates the best paths to destinations.
Link-state protocols are sometimes called shortest path first or distributed-database protocols. They are built on the Dijkstra shortest path algorithm, an algorithm from graph theory that was developed by E.W. Dijkstra. Because link-state protocols send only the state of their own links to all routers, and distance vector protocols send full routing tables to their neighbors, it can be said that link-state algorithms send small updates everywhere, while distance vector algorithms send larger updates only to neighboring routers. Link-state protocols are usually more CPU-and memory-intensive than distance vector routers. The following is a list of link-state routing protocols (including non-IP):
• IP Open Shortest Path First (OSPF)
• CLNS and IP Intermediate System-to-Intermediate System (IS-IS)
• IPX NetWare Link-Services Protocol (NLSP)
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