Global Anycast NAT64 Well-Known Prefix

This document defines a globally routable, anycast NAT64 service using the IPv6 prefix 2600:6464::/96 as a standardized translation substrate for IPv6-to-IPv4 connectivity. The goal of this specification is to eliminate per-network NAT64 configuration complexity by introducing a single globally consistent NAT64 translation prefix operated as a distributed anycast service by participating Internet Service Providers, cloud providers, and content delivery networks. The model assumes an IPv6-only client environment with mandatory IPv4 reachability via NAT64 translation. IPv4-only services remain reachable without modification. IPv4 is not modified. IPv6 is not modified. Only translation placement and routing semantics are standardized. This document defines: * A globally shared NAT64 prefix (2600:6464::/96) * Anycast-based NAT64 edge behavior * Stateless IPv6-to-IPv4 synthesis rules * Optional reverse mapping constraints (IPv4->IPv6 blocked) * Operational requirements for participating networks