Border Gateway Protocol (BGP)
Also known as: border gateway protocol
The routing protocol that exchanges reachability information between autonomous systems and steers traffic across the internet.
BGP is the protocol that networks use to tell each other which IP prefixes they can reach and by which path. It is a path-vector protocol: each announcement carries the sequence of ASNs (the AS-path) the route has traversed, which BGP uses both to prevent loops and to choose between paths.
Because BGP was designed to trust its neighbors, a network can announce address space it does not legitimately hold - the basis of BGP hijacking. Layered defenses such as RPKI origin validation, ASPA, and IRR filtering exist to reduce that risk.
The global BGP table currently holds close to a million IPv4 prefixes and continues to grow. Route collectors around the world archive it so its evolution can be analyzed over time.