RFC 4271 / START HERE
BGP, before the details
BGP: Border Gateway Protocol
BGP lets networks announce which IP destinations they can reach. Version 4 is used between independently operated networks on the Internet.
The idea in one picture
A network announces reachability
Neighbors apply routing policy
Routes guide traffic onward
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
There is no single router with a complete plan for the Internet. Networks exchange reachability and apply their own routing policies.
A familiar example
An Internet provider learns which neighboring network offers a route toward a website's address range.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Establish a BGP sessionBGP runs over TCP and exchanges OPEN and KEEPALIVE messages before routing updates.→
- Advertise and withdraw prefixesUPDATE messages carry withdrawals, path attributes, and reachable prefixes.→
- Use AS paths to detect loopsAS_PATH records autonomous-system traversal information and supports loop detection.→
- Select routes using policy and reachabilityBGP’s decision process separates received routes, a selected local route, and exported routes.→
- Handle failures without assuming route truthSession and UPDATE errors require specified handling, and transport protection is distinct from route authorization.→
This introduction explains RFC 4271 (2006). Read the original RFC ↗