What is Open Shortest Path First (OSPF)?


OSPF is a non-proprietary routing protocol and it is used as an Interior Gateway Protocol (IGP) for the Internet. It was developed by the Interior Gateway Protocol (IGP) working group of the Internet Engineering Task Force (IETF).

The OSPF protocol is a link-state routing protocol that means that the routers exchange topology and network information with their nearest neighbors. This network information provides a complete map of the AS group to each router and then the routers are able to calculate end to end paths throughout the network. Therefore, the next hop address to which data is forwarded is determined by choosing the best path to reach the required destination. Being a Link State Routing Protocol it is able to converge more quickly and is less prone to Routing Loops.

OSPF protocol was created with the mindset to provide an alternative to RIP. In shortest path first algorithm a path tree describes the network topology to define the shortest path from each router to each possible destination address.

The main advantage of OSPF is that the routers share a complete topology of the network which allows routers to calculate routes that satisfy particular criteria for QoS. Also network updates are only sent when there is a change in the network.

Its main disadvantage is that it does not scale well as the network grows larger. Because when the number of routers increases so does the size and ratios of topology updates and the amount of time needed to calculate paths. This in turn needs more CPU power and memory usage. This lack of scalability makes it unsuitable for routing across the Internet at large.