Difference Between BGP and OSPF

BGP (Border Gateway Protocol) and OSPF (Open Shortest Path First) are two popular computer network routing protocols. While both protocols are used to route traffic between networks, their functions and characteristics are different.

OSPF is an interior gateway protocol (IGP) that is designed to be used within a single autonomous system. BGP is an exterior gateway protocol (EGP) designed for use between different autonomous systems.

Read this article to find out more about BGP and OSPF and how they are different from each other.

What is BGP?

BGP is an exterior gateway protocol (EGP) that determines the best path for data transmission between Autonomous Systems (AS). This happens through the exchange of routing information in the form of BGP messages, which contain information on the network topology, the availability of various routes, and the policies used to determine the best path.

  • BGP is a path-vector protocol, which means it considers a variety of features, including network policies, routing metrics, and other considerations, to select the best path

  • BGP operates on top of the TCP/IP protocol and communicates between routers through TCP port 179. When a BGP router becomes online, it establishes a TCP connection with its neighbour routers and shares network topology information. This data is used to build a BGP routing table, which consists of a list of all possible routes to various destinations as well as the attributes associated with each route.

  • One of BGP's important features is its ability to support various route selection policies. These policies can be used to manage traffic flow between ASes and ensure that traffic is routed through the most efficient path. BGP policies can be based on factors such as a preference for a particular network path, the availability of backup routes, and transmission costs.

  • BGP also supports several types of BGP messages, including update, keep-alive, and notification messages. Keep-alive messages are used to keep the TCP connection between routers alive, while update messages are used to announce new routes or modify existing routes. Notification messages are used to notify issues or to terminate a BGP session.

What is OSPF?

OSPF (Open Shortest Path First) is a protocol for exchanging routing information on a computer network within a single autonomous system (AS). It is a popular interior gateway protocol (IGP) in large industrial networks.

  • OSPF uses link-state routing, which means that routers share network topology information, such as the availability and cost of multiple routes. This data is used to create a network map, which allows routers to find the shortest path between any two points on the network. OSPF gives comprehensive data about the entire path to a destination, as opposed to distance vector protocols, which just provide information about the next hop.

  • OSPF uses a hierarchical network structure, with routers divided into areas. Each area has its own link-state database, which provides information about the area's routers and links. Routers within an area share connection information with one another, but they do not exchange information with routers in other areas unless they are designated as area border routers (ABRs) or backbone routers.

  • ABRs are responsible for exchanging routing information between areas. They maintain a summary of the routes in their area and distribute it to other ABRs and backbone routers. This allows routers in different areas within the AS to determine the fastest route to a destination.

  • OSPF supports multiple types of routers, including internal routers that are placed within an area and backbone routers that are located within the network's backbone area. OSPF also supports other OSPF message types, such as hello messages, link-state advertisement (LSA) messages, and SPF (Shortest Path First) calculation messages. Hello messages are used to discover and maintain adjacencies between routers, whereas LSA messages are utilized for transmitting network topology information. The shortest path to a destination is calculated using SPF calculation messages.

  • OSPF also supports multiple metrics for determining route costs, including bandwidth, delay, reliability, load, and MTU (Maximum Transmission Unit). These measures are used to determine the shortest path between two network points.

Difference between BGP and OSPF

The following table highlights the major differences between BGP and OSPF −




Full Form

Border Gateway Protocol (BGP)

Open Shortest Path First (OSPF)


Exterior Gateway Protocol (EGP)

Interior Gateway Protocol (IGP)

Method of Routing

Path-Vector Protocol

Link-state protocol

Network Topology

BGP supports flat or hierarchical network topologies.

OSPF supports hierarchical network topologies.




Port Number

BGP port number is 179.

OSPF port number is 89


It uses the best path algorithm.

It uses the Dijkstra algorithm.


It uses update messages, keep-alive messages, and notification messages.

It uses hello messages, link-state advertisement messages, and SPF calculation messages.


In conclusion, BGP and OSPF are two different routing protocols used in computer networks for multiple purposes.

OSPF is an interior gateway protocol that determines the shortest path between network routers within a single AS, whereas BGP is an exterior gateway protocol that determines the ideal route for data transmission across the internet between multiple ASes

OSPF is regularly updated and uses link-state routing, whereas BGP is a path-vector routing protocol that takes longer to converge. The appropriate protocol is chosen based on the unique network requirements and topology.

Updated on: 14-Apr-2023


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