Routers connect networks using the Internet Protocol (IP), and OSPF (Open Shortest Path First) is a router protocol used to find the best path for packets as they. Open Shortest Path First (OSPF) is an intra-domain routing protocol based on the Link State (LS) algorithm. The first two versions are used with IPv4, while. Open Shortest Path First (OSPF) Open Shortest Path First (OSPF) is an Interior Gateway Protocol (IGP) standardized by the Internet Engineering Task Force (IETF) and commonly used in large Enterprise networks. OSPF is a link-state routing protocol providing fast convergence and excellent scalability.


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Rather than simply counting the number of router hops between hosts on a network, as RIP does, OSPF bases its path choices on "link states" that take into account additional network information, including IT-assigned cost metrics that give some paths higher assigned costs.

What is OSPF (Open Shortest Path First)? - Definition from

For example, a satellite link may be assigned higher cost than a wireless WAN link, which in turn may be assigned higher cost than a metro Ethernet link. For forming a neighbor relationship between, the interfaces used to form the relationship must be in the same OSPF area.

While an interface may be configured to belong to multiple areas, this is generally not practiced. When configured in a second area, an interface must be open shortest path first protocol as a secondary interface.

What is Open Shortest Path First (OSPF) - Definition from Techopedia

Adjacency state machine[ edit open shortest path first protocol Each OSPF open shortest path first protocol within a network communicates with other neighboring routers on each connecting interface to establish the states of all adjacencies. Every such communication sequence is a separate conversation identified by the pair of router IDs of the communicating neighbors.

During its course, each router conversation transitions through a maximum of eight conditions defined by a state machine: The state down represents the initial state of a conversation when no information has been exchanged and retained between routers with the Hello Protocol.

The Attempt state is similar to the Down state, except that a router is in the process of efforts to establish a conversation with another router, but is only used on NBMA networks.

The Init state indicates that a HELLO packet has been received from a neighbor, but the router has not established a two-way conversation.

The 2-Way state indicates the establishment of a bidirectional conversation between two routers. This state immediately precedes the establishment of adjacency.

This is the lowest state of a router that may be considered as a Designated Router. The ExStart state is the first step of adjacency of two routers.

In the Exchange state, a router is sending its link state database information to the adjacent neighbor. At this state, a router open shortest path first protocol able to exchange all OSPF routing protocol packets.

In the Loading state, a router requests the most recent Link-state advertisements LSAs from its neighbor discovered in the previous state. The Full state concludes the conversation when the routers are fully adjacent, and the state appears in all router- and network-LSAs.


The link state databases of the neighbors are fully synchronized. OSPF defines five different message types, for various types of communication: Hello Hello messages are used as a form of greeting, to allow a router to discover other adjacent routers on its local links and networks.

The messages establish relationships between neighboring devices called adjacencies and communicate key parameters about how OSPF is to be used in open shortest path first protocol autonomous system or area. During normal operation, routers send hello messages to their neighbors at regular intervals the hello interval ; if a router stops receiving hello messages from a neighbor, after a set period the dead interval the router will assume the neighbor has gone down.

Database Description DBD Open shortest path first protocol description messages contain descriptions of the topology of the autonomous system or area.

Open Shortest Path First

They convey the contents of the link-state database LSDB for the area from one router to another. Communicating a large LSDB may require several messages to be open shortest path first protocol by having the sending device designated as a master device and sending messages in sequence, with the slave recipient of the LSDB information responding with acknowledgements.

The message specifies the link s for which the requesting device wants more current information.