To keep it simple, Border Gateway Protocol, or BGP, is essentially what holds the internet together through the exchanging of routes.The Border Gateway Protocol is a routing protocol that is made to connect and trade information between autonomous systems, or AS’s through peering. BGP is a Layer 4 path vector routing protocol which is designed to make routing decisions based on the intended paths, following rules implemented by network administrators, as well as applied policies.
BGP exchanges information, communicating on how to reach designated end points, trading contacts, and more.It is a tool of internet service providers that dispatches traffic throughout the internet, making it a crucial, scalable, and complex protocol. BGP relies on TCP, and it is responsible for informing all hosts that need to know of the ways a packet can travel from site A to site B – and, if a site or router goes down, how to reroute the packet so that it will still reach its destination. As the internet grows ever larger and becomes ever more complex, having a well-configured BGP is crucial to keeping everything running smoothly. Without BGP, static routes would be needed among all the major ISPs. In the absence of BGP, as network topologies changed, those routes would also need to be changed; clearly, this is an impossible task in a network as large as the internet now is.
Implemented in the early 90’s, BGP is currently on it’s 4th version, which is BGP4. Originally designed to route traffic, BGP has retained its position as a vital protocol in the networking world. There are two unique forms of BGP which are External Border Gateway Protocol (eBGP) and Internal Border Gateway Protocol (iBGP). Internal BGP refers to the running of two or more peers within the same AS while External BGP routers peer between different autonomous systems. Internal BGP handles the internal routing throughout a network, whereas eBGP has the ability to route externally. BGP has a route storage function that retains information on communication and transferability between networks, as well as advertisement and selection to keep routes current and relevant. BGP essentially acts as GPS, indicating where to go and choosing quick and effective routes.
When an organization needs to connect to multiple Internet Service Providers, BGP is there to assist in finding the shortest route between autonomous systems. It is essentially the navigation for networks, taking into consideration the length or a route, as well as accessibility and ease of traffic. Enabling BGP means routers will search and utilize the shortest path and add them to your organization's routing table which will be stored in a networks RIB, or Routing Information Base.