1. Introduction

1. Introduction

With the exhaustion of the unallocated IPv4 address pools, it will be difficult for many networks to assign IPv4 addresses to end users.

This document describes an IPv4-over-IPv6 solution as one of the techniques for IPv4 service extension and encouragement of IPv6 deployment. 464XLAT is not a one-for-one replacement of full IPv4 functionality. The 464XLAT architecture only supports IPv4 in the client-server model, where the server has a global IPv4 address. This means it is not fit for IPv4 peer-to-peer communication or inbound IPv4 connections. 464XLAT builds on IPv6 transport and includes full any-to-any IPv6 communication.

The 464XLAT architecture described in this document uses IPv4/IPv6 translation standardized in [RFC6145] and [RFC6146]. It does not require DNS64 [RFC6147] since an IPv4 host may simply send IPv4 packets, including packets to an IPv4 DNS server, that will be translated to IPv6 on the customer-side translator (CLAT) and back to IPv4 on the provider-side translator (PLAT). 464XLAT networks may use DNS64 [RFC6147] to enable single stateful translation [RFC6146] instead of 464XLAT double translation where possible. The 464XLAT architecture encourages the IPv6 transition by making IPv4 services reachable across IPv6-only networks and providing IPv6 and IPv4 connectivity to single-stack IPv4 or IPv6 servers and peers.