BGP ( Border Gateway Protocols )

BGP (Border Gateway Protocol) is protocol that manages how packets are routed across the internet through the exchange of routing and reachability information between routers. Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information between autonomous systems (AS) on the Internet. The protocol is often classified as a path vector protocol but is sometimes also classed as a distance-vector routing protocol.

You can think of an autonomous system in the computer world as a city with many streets. A network prefix is similar to one street with many houses. An IP address is like an address for a particular house in the real world, while a packet is the equivalent of a car traveling from one house to another using the best possible route. Taking this comparison to its logical conclusion, the BGP routing protocol is analogous to your trusty GPS navigator. Like Google’s Waze application, the best route is determined by different factors, such as traffic congestion, roads temporarily closed for maintenance, etc. The path is calculated dynamically depending on the situation of the network nodes, which are like roads and junctions on a GPS map. Just like in real life, usually more than one route exists to reach a given destination. BGP is responsible for determining the most suitable route according to the information collected and an organization’s routing policy, which is based on cost, reliability, speed, etc.

BGP makes best-path decisions based on current reachability, hop counts and other path characteristics. In situations where multiple paths are available -- as within a major hosting facility -- BGP can be used to communicate an organization's own preferences in terms of what path traffic should follow in and out of its networks. BGP even has a mechanism for defining arbitrary tags, called communities, which can be used to control route advertisement behavior by mutual agreement among peers.