IPv4.5: A Locator/Identifier-Separated Extension to IPv4 with Post-Quantum Session Security

The global IPv4 address space was exhausted at the IANA level in 2011, and Carrier-Grade NAT (CGN) has since served as the primary operational workaround. CGN preserves connectivity but violates the end-to-end principle, complicates application development, and introduces substantial operational overhead. This document specifies IPv4.5, a pragmatic extension of IPv4 that introduces a 96-bit address space organized as a Locator/Identifier separation: a 32-bit IPv4 Locator, a 16-bit Site Identifier, and a 48-bit Endpoint Identifier. IPv4.5 packets are encapsulated in UDP (port 4242) for transparent transit through existing IPv4 routers, NAT devices, and firewalls without requiring infrastructure changes. Session security is established through a hybrid post-quantum key exchange combining ML-KEM-768 [FIPS203] and X25519 [RFC7748], performed once per session. Subsequent data protection uses symmetric AEAD ciphers (AES-256-GCM or ChaCha20-Poly1305). The design enforces strict separation of concerns across four independent planes: data, control, identity, and cryptographic. Higher-level functions such as semantic routing and self-sovereign identity are explicitly out of scope for this specification.