Native IPv6 behind IPv4-to-IPv4 NAT Customer Premises Equipment (6a44)

Abstract

In customer sites having IPv4-only Customer Premises Equipment (CPE), Teredo (RFC 4380, RFC 5991, RFC 6081) provides last-resort IPv6 connectivity. However, because it is designed to work without the involvement of Internet Service Providers, it has significant limitations (connectivity between IPv6 native addresses and Teredo addresses is uncertain; connectivity between Teredo addresses fails for some combinations of NAT types). 6a44 is a complementary solution that, being based on ISP cooperation, avoids these limitations. At the beginning of 6a44 IPv6 addresses, it replaces the Teredo well-known prefix, present at the beginning of Teredo IPv6 addresses, with network-specific /48 prefixes assigned by local ISPs (an evolution similar to that from 6to4 to 6rd (IPv6 Rapid Deployment on IPv4 Infrastructures)). The specification is expected to be complete enough for running code to be independently written and the solution to be incrementally deployed and used.