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OSPF and BGP routing protocols explained

To understand routing protocols, one must first know what routing is and the role it serves in networking. In the most basic terms, routing is the process used by computer networking devices to determine which paths on a network to send traffic on.  

Essentially, routing protocols are a set of rules or algorithms that instruct routers on a network how to communicate and exchange information with each other in order to select the best paths to send traffic on.

As the Internet is one big WAN (Wide Area Network) made up of hundreds of thousands of LANs (Local Area Networks), it is necessary to enable these networks to communicate with each other, otherwise the Internet would not be able to function. Routing protocols make this communication possible.

There are a number of different routing protocols, each with its own set of rules and standards. Some common routing protocols include Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), Routing Information Protocol (RIP), Distance Vector, Internet Gateway Routing Protocol (IGRP), Link State, and Enhanced Inter Gateway Routing Protocol (EIGRP), to name a few.
There are a number of different routing protocols, each with its own set of rules and standards. This article explains two common ones – BGP and OSPF.

In this article, I’ll provide an explanation and some common uses for the OSPF and BGP routing protocols.

Open Shortest Path First (OSPF)

OSPF is a link state routing protocol for Internet Protocol (IP) networks. It is a type of intra-domain routing protocol that operates within a single autonomous system (AS). This means that routing happens only within a single routing domain, not on the Internet level.

OSPF is the most commonly used Interior Gateway Protocol in large enterprise networks. It works by calculating the fastest path between the source and destination and then sends packets of data on a route that has the least amount of traffic. The “shortest path” refers to the fact that information is not necessarily sent over a route that is the shortest distance-wise, but shortest in terms of the time it takes for data packets to travel from point A to point B.

A few key reasons for implementing OSPF routing include:

  • Reducing routing overheads for companies

  • Achieving network redundancy

  • Optimising performance of local area networks

Border Gateway Protocol (BGP)

BGP is a routing protocol used to make routing decisions on the Internet. Without BGP, the Internet would not be able to work, it’s how your email and web requests are routed across the world wide web. BGP is responsible for exchanging routing information between gateway hosts in a network of autonomous systems, or in other words – it establishes routing between users and allows for peering and carrier networks to connect.

BGP is often used by Internet Service Providers, especially if they are multihomed, to enable routing of traffic between each other’s networks, making BGP one of the most used and important protocols of the Internet.

For example, GCOMM uses the BGP routing protocol to enable customers to have more control over how their networks are advertised to their providers, as well as to help optimise network performance.

Some other advantages of BGP routing include:

  • Achieving redundancy

  • Preventing traffic from being sent across an expensive and low capacity link

Since it was created, BGP has gone through three versions. The most current version is BGP4 and it is supported by most router manufacturers, including Cisco and Juniper, among many others.