BGP (Border Gateway Protocol)

Border Gateway Protocol (BGP) is a standardized protocol used on the internet to exchange routing information between different autonomous systems (AS), essentially determining the best path for data packets to travel across the internet by allowing networks to communicate and choose the most efficient route for data transmission between them; it acts as the primary mechanism for internet routing, enabling data to reach its destination across various networks by considering factors like network performance and policies set by network administrators.

Key points about BGP:

• Function: BGP facilitates communication between different autonomous systems (ASes) and independent networks managed by different organizations. It enables them to share routing information and decide the best path for data packets to reach their destination.
• Exterior BGP (eBGP): This is BGP's primary function, where routers on the edge of different ASes exchange routing information to determine the optimal route between them.
• Interior BGP (iBGP): While less common, iBGP can be used within a single AS to distribute routing information among routers within that network.
• Path Vector Protocol: BGP is considered a path-vector protocol, meaning it builds a routing table based on the "path" or sequence of ASes a packet must traverse to reach its destination.
• BGP Attributes: BGP uses attributes like AS path, local preference, origin, and weight to evaluate different routes and select the best one based on network policies and priorities.

How BGP works:

1. Establishing BGP sessions: Routers on the edge of different ASes establish BGP sessions with each other to exchange routing information.

2. Sending updates: When a network topology changes, a BGP router sends update messages to its peers, informing them about the new reachable networks and their associated routes.

3. Route selection: Each router analyzes the received BGP updates, considering the associated attributes, and chooses the best path to reach a particular network based on its configured policies.

Importance of BGP:

• Scalability: BGP enables efficient routing across the vast and complex internet infrastructure, handling large numbers of networks and routes.
• Flexibility: Network administrators can customize BGP policies to prioritize certain routes based on performance, cost, or security factors.
• Reliability: BGP uses keep alive messages to maintain connection stability and quickly detect network failures.

This post is covered in Network+.