Open Shortest Path First (OSPF)

      Open shortest path first (OSPF) fixes many of issues with RIP and allows routes to be selected dynamically based on the current state of the network. It is complement of RIP. One issue with RIP is limit of its ability to choose the best route and adapt to changing network conditions. Another problem is cost value of 16 for infinity, which makes it possible to use RIP in situation where more than 15 hops might occur between devices.

      This protocol name conveys two important characteristics. The first word refers to the fact that the protocol was developed using open and public RFC process, no license is required to use it. The SPF portion of the name refers to the type of algorithm it uses, which is designed to allow routers to dynamically determine the shortest path between any two networks. 

Overview of OSPF Operation 

    1) The main concept used by OSPF is link state database (LSDB). Each router in the network maintains a data structure called linked database which contain information about the current status of the network. It also describe the link to other network structure in directed graphs, hop count or cost. 

    2) When changes occur in the internetwork, one router update the status of their network to the another routers via link advertisements which are messages to manage the link database.

    3) To determine final router, each router uses its link database to find out shortest path tree. This tree shows the shortest path from one router to another.

    4) As the new information about the router updates, this shortest path tree can be recalculated.

    5) So we can say that OSPF adjust the best route dynamically.

    6) There may be a case, when two paths exist with an equal cost. In this case, traffic or data can be shared between both routes.

OSPF Advantages

1)    Support authentication for security.

2)     Support classful, classless, subnet classful IP addressing.

3)    For large internetwork, OSPF arranged the routes in grouped or hierarchical topology.

4)    It reduced the link state traffic by choosing the shortest path.

5)    Better organization.

OSPF Drawbacks

1)    Complexity

2)    Need more work to properly maintain a internetwork.

Networking: Cisco Packet Tracer Networking: Implement Open shortest path first (OSPF)