BGP: A Quick Overview

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BGP, or Border Gateway Protocol, is the routing protocol that makes the internet work. It’s responsible for finding the best paths for IP prefixes (think of them as groups of IP addresses) across the vast network of Autonomous Systems (ASes) that make up the internet. An AS can be thought of as a network controlled by a single entity, like a large internet service provider or a multinational corporation.

What makes BGP special?

• It operates at Layer 4: Unlike many routing protocols that work at Layer 3 (the network layer), BGP sits on top of TCP/IP. This provides increased reliability and allows BGP to traverse complex network topologies.
• Path Awareness: BGP doesn’t just find a route, it finds many. BGP speakers (routers that run BGP) exchange information about entire paths to a destination, including attributes like the number of ASes the path traverses (AS path length), weight, and local preference. This allows for sophisticated route selection based on various criteria.
• Best “Path” Selection: Each BGP speaker maintains a BGP table containing all the learned paths. From this table, the “best” path for each prefix is selected based on a set of well-defined rules and attributes. This ensures efficient and optimized routing across the internet.

Want to learn more?

This is just a brief overview of BGP. To dive deeper into the intricacies of BGP path selection and attributes, check out this excellent resource: BGP Attributes and Path Selection