BGP

Border Gateway Protocol (BGP) is the routing protocol that exchanges reachability information between autonomous systems on the internet — it is how every network announces which IP ranges it serves and learns paths to everyone else.

Cloud providers participate in BGP as their own autonomous systems, peering with other networks at exchange points and selling transit. Anycast services, DDoS mitigation, and traffic engineering are all implemented through BGP announcements — withdrawing a site's announcement moves its traffic elsewhere in seconds.

For buyers, BGP matters indirectly but concretely: a provider's peering policy, its number of exchange points, and its transit mix determine the latency and resilience of every connection. Providers that publish peering information and route statistics are generally the ones worth trusting with production traffic.