OSPF is a link state routing protocol. OSPF is based on the distributed map concept all nodes have a copy of the network map, which is regularly updated. Each node contains a routing directory database. This database contains information about the routers interfaces that are operable, as well as status information about adjacent routers. This information is periodically broadcast to all routers in the same domain.

The OSPF computes the shortest path to the other routers. OSPF protocol is now widely used as the interior router protocol in TCP/IP networks. OSPF computes a route through the internet that incurs the least based on a user-configurable metric of cost. The user can configure the cost to express a function of delay, data rate, or other factors.

OSPF is able to equalize loads over multiple equal cost paths. OSPF is classified as an internal gateway protocol (IGP) because it support routing within one autonomous system only. The exchange of routing information between autonomous systems is the responsibility of another protocol an external gateway protocol (EGP). OSPF can support one or many networks.

Features of the OSPF

1.OSPF supports multiple circuit load balancing because it can store multiple routes to a destination.

2.OSPF can converge very quickly to network topology change.

3.OSPF support multiple metrics loops.

4.OSPF is not susceptible to routing loops.

5.OSPF support for variable length subnetting by including the subnet mask in the routing message.