OSPF, Open Shortest Path First

Open Short Path First or OSPF, is the most widely used IGP (Interior Gateway Protocol) in large corporate networks. It is able to communicate with other routers regarding the best traveling paths, possibly using a clear text password or MD5 hash function for authentication. Unlike RIP (Routing Information Protocol), a process in which the entire routing table is forwarded, a host implementing OSPF only multicasts updated information when changes in the routing table have occurred. Instead of counting the number of hops, OSPF uses link-state to base path descriptions derived from additional network information. It allows cost metrics to be assigned to specific routers so that some paths are given special preference. OSPF also supports a subnet mask so that a network may be subdivided. OSPF uses RIP to support router-to-end station communication. Several manufacturers now include RIP support within their routers designed for OSPF. This is because so many networks commonly have RIP already in use.