BGP hijack
An ASN announces an IP prefix it doesn't own — by mistake or on purpose — and traffic gets routed the wrong way.
Classic incidents: Pakistan Telecom (2008, accidentally took YouTube offline globally for 2 hours), China Telecom (2010, routed 15 % of internet traffic via China for 18 minutes), AWS Route 53 (2018, crypto theft via DNS-route hijack). Two flavours: origin hijack (claim "I own 8.8.8.0/24") and path hijack (manipulate the AS path to look closest). Mitigations: RPKI/ROV, BGPsec, peering filters, BGP monitoring (Cloudflare Radar, BGPmon).