BGP

BGP (Border Gateway Protocol), standardized as RFC 4271, is the path-vector routing protocol that autonomous systems use to advertise which networks they can reach and how to get there. It is the glue of the public internet: every network operator runs BGP to tell the rest of the world what address space it owns and to learn the best paths to everyone else. Without it, there is no coherent map of how independently operated networks connect.

• Path-vector routing - BGP advertises full AS-paths rather than simple metrics, which lets it avoid loops and encode routing policy along the way.
• Autonomous system peering - Routes are exchanged between ASes over TCP sessions, making BGP the language of interconnection between ISPs, cloud providers, and large enterprises.
• Policy over shortest-path - Operators shape traffic with local preferences, AS-path prepending, and communities, so business relationships — not just distance — decide routing.
• Global reachability - The aggregate of everyone’s BGP advertisements is the internet’s routing table, the substrate every API call ultimately traverses.

BGP rarely appears in an API design discussion, but it is the layer every API depends on: a request to an API endpoint only arrives because BGP has propagated a route to that endpoint’s network. When a major BGP misconfiguration or route leak happens, entire platforms and their APIs go dark regardless of how well the API itself is built. Understanding BGP matters for anyone reasoning about API availability, latency, anycast-based edge delivery, and the blast radius of internet-scale outages that no amount of application-layer resilience can fully absorb.