BGP
Border Gateway Protocol: the routing protocol between networks (autonomous systems).
Roughly speaking, if DNS is the Internet's address book, then BGP is the Internet's road map. -- Cloudflare
Anycast
Multiple instances share the same IP; BGP routes each client to the nearest one.
BGP Hijack
Attackers falsely announce ownership of IP prefixes they do not actually control, so traffic is routed to them.
Case: Iraq blocks Telegram
Iraq Blocks Telegram, Leaks Blackhole BGP Routes
Iraq hijacked Telegram's traffic by BGP hijack to block it, but the route leaked outside Iraq. Disruption was minimized by Telegram's use of RPKI (route origin validation).