A border gateway protocol is a set of rules for constructing the best network route for data transmission in the Internet.
Since the Internet consists of various kinds of corporate, private, public, and other diverse networks, data transmission is usually accomplished using transit points. For example, when a user in the United States needs to download information that is physically located on a German server, the data usually travels via a whole chain of networks before reaching its destination.
The function of BGP is to analyze all possible routes and select the optimal one. When selecting a route, the border gateway protocol takes into account the geographic location of servers, the network load, and the cost of the connection.
BGP is directly related to the concept of “autonomous system”. An autonomous system refers to a system of IP networks and routers under the control of one or more service providers. For example, each service provider or ISP registers its infrastructure and networks as an autonomous system. This requires obtaining a special autonomous system number from the local (LIR) or regional Internet registry (RIR).
Communication between autonomous systems in the Internet is carried out using the Border Gateway Protocol (BGP).