BGP (Border Gateway Protocol) is a standardized routing protocol used in computer networks to exchange routing and reachability information between autonomous systems (ASes). An autonomous system is a collection of IP networks and routers under a single administrative entity.
BGP plays a crucial role in the functioning of the internet, as it helps determine the best paths for routing data packets between different autonomous systems. Unlike interior gateway protocols (IGPs) that focus on routing within a single network, BGP is an exterior gateway protocol designed for inter-domain routing.
Key characteristics of BGP include:
- Path Vector Protocol: BGP maintains a list of autonomous systems that a route traverses, forming a “path vector.” This information helps prevent routing loops and ensures accurate path selection.
- Policy-Based Routing: BGP allows network administrators to define routing policies based on various factors, such as preferred paths, traffic load balancing, and avoiding specific networks.
- Path Attributes: BGP uses attributes associated with each route to make routing decisions. Examples of attributes include AS path length, origin, next-hop IP address, and others.
- Path Selection: BGP employs a decision process that considers various attributes to choose the best path for a route. The decision is based on factors such as the shortest AS path, the lowest origin type, and other configurable criteria.
- Route Aggregation: BGP supports route aggregation, allowing multiple IP prefixes to be represented as a single summarized route. This helps reduce the size of the routing tables and improves efficiency.
It is essential for ensuring the stability, scalability, and efficiency of the global internet routing system. It enables internet service providers (ISPs), data centers, and large networks to communicate and exchange routing information to deliver data packets accurately and reliably between different parts of the internet.