About Open shortest path first (OSPF) Protocol

Open shortest path first (OSPF) Protocol is a link state routing  protocol and open standard protocol mean to say that it can be used with any vendor  not like EIGRP. it is interior gateway routing protocol used to distribute routing information with in an autonomous system. In OSPF if changed occur in the network then router will multicast the routing information to all the nodes in the network. so that all nodes will be the same routing information .

OSPF uses Dijkstra uses algorithm to find the best route in the network to forward packet from source to destination . it is uses SPF tree for route calculation to find the neighbor.

About OSPF

Open shortest path first (OSPF) Protocol


OSPF Properties-:

  • It is classless so it support VLSM/CIDR.
  • It has unlimited Hop count.
  • It is support multiple vendor .
  • Minimising routing update traffic.
  • Allow scalability.
  • Its A.D value 110.
  • It support equal cast load balancing .
  • It is also support authentication.
OSPF metric-: To maintain and manage network it create three table .
Neighbour table- It store the information about neighbour ID and their  status up/ down . it is the list of all router for which hello packet has been sent.
Topology table- It store the information about topology which using in the network and also keep the information about alternate route to reach the destination.
Routing table-: It store the information about the best route and all possible route. It is generated when the when algorithm run on the link state database. each router has unique routing table.

OSPF Terminology 

OSPF area
OSPF allow the autonomous system divided up in to contiguous group of network  and router . In the network all router which is connected in the same area share the same area ID. it has the range of 0 to 4.2 billion . all  router have same topology table which is associated with same area

Router ID

Router ID used to identify the Router in the OSPF network. It is the highest  IP address which is configure on the all loopback interface . if there is no any loopback interface configure with IP address then it will choose highest IP address from active interface.


Link is an router interface which is connect with any network when any new interface will connect connect to the OSPF process then that is considered by OSPF as a link


EIGRP share directly route with all its neighbour when neighbour will become adjacent but OSPF will not directly share its routes with neighbour until that have also establish adjacencies . it is a listing of all neighbour 
to which router have establish bi-directional communication.
Link state Advertisement

Link state advertisement(LSA) contain Link  state and routing information . Router used LSA to learn topology of entire network . LSA send when change occur in the topology.

Related Topics

See also-:  OSPF .PPT File
blished bi-directional communication

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Rakesh Kumar
Rakesh Kumar is a Network engineer and a Blogger. He is crazy for learn and write about Technology , Tech and Computer Tips and Tricks Blog.