A Border Gateway Protocol 4 (BGP-4)
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Y. Rekhter, T. Li, S. Hares · 2006-01
Abstract
BGP-4 is an inter-domain path-vector routing protocol that exchanges reachability information among Autonomous Systems using TCP sessions on port 179. It carries prefix advertisements with associated path attributes (AS_PATH, NEXT_HOP, LOCAL_PREF, MED) that allow policy-based route selection. RFC 4271 obsoletes RFC 1771.
Why This RFC Matters
BGP-4 is the routing protocol of the global Internet, responsible for exchanging reachability information among more than 90,000 Autonomous Systems. Every packet crossing an AS boundary is forwarded based on BGP routing decisions. Its flexible policy model—through communities, route maps, and path attributes—allows carriers and enterprises to implement complex traffic-engineering and peering policies. Understanding BGP is fundamental to understanding Internet architecture, routing security (RPKI, BGPsec), and outages caused by route leaks or hijacks.