OSPF is an interior gateway protocol (IGP) that routes packets within a single autonomous system (AS). OSPF uses link-state information to make routing decisions, making route calculations using the shortest-path-first (SPF) algorithm (also referred to as the Dijkstra algorithm). Each router running OSPF floods link-state advertisements throughout the AS or area that contain information about that router’s attached interfaces and routing metrics. Each router uses the information in these link-state advertisements to calculate the least-cost path to each network and create a routing table for the protocol.

It specifies the type of OSPF packet. There are 5 different types of OSPF packets. (1-byte)

    1- Hello packet
    2- Database Descriptor packet
    3- Link State Request packet
    4- Link State Update packet
    5- Link State Acknowledgment packet