Open Shortest Path First (OSPF) is a link-state routing protocol that was developed for IP networks and is based on the Shortest Path First (SPF) algorithm. OSPF is used to distribute IP routing information throughout a single Autonomous System (AS) in an IP network. Here are some key features of OSPF:

• OSPF is a classless routing protocol that supports Variable Length Subnet Masks (VLSM), Classless Inter-Domain Routing (CIDR), manual route summarization, and equal cost load balancing.
• OSPF uses only one parameter as the metric, which is the interface cost.
• The administrative distance of OSPF routes is, by default, 110.
• OSPF uses multicast addresses 224.0.0.5 and 224.0.0.6 for routing updates.
• OSPF uses the concept of areas, which are logical groupings of contiguous networks and routers. All routers in the same area have the same topology table, but they don’t know about routers in the other areas. The main benefits of creating areas are that the size of the topology and the routing table on a router is reduced, less network traffic is generated, and routing information is hidden from routers in other areas.

OSPF is a widely deployed routing protocol that can converge a network in a few seconds and guarantee loop-free routing.