1. Introduction

This document specifies DNS64, a mechanism that is part of the toolbox for IPv4-IPv6 transition and coexistence. DNS64, used together with an IPv6/IPv4 translator such as stateful NAT64 [RFC6146], allows an IPv6-only client to initiate communications by name to an IPv4-only server.

DNS64 is a mechanism for synthesizing AAAA resource records (RRs) from A RRs. A synthetic AAAA RR created by the DNS64 from an original A RR contains the same owner name of the original A RR, but it contains an IPv6 address instead of an IPv4 address. The IPv6 address is an IPv6 representation of the IPv4 address contained in the original A RR. The IPv6 representation of the IPv4 address is algorithmically generated from the IPv4 address returned in the A RR and a set of parameters configured in the DNS64 (typically, an IPv6 prefix used by IPv6 representations of IPv4 addresses and, optionally, other parameters).

Together with an IPv6/IPv4 translator, these two mechanisms allow an IPv6-only client to initiate communications to an IPv4-only server using the Fully Qualified Domain Name (FQDN) of the server.

These mechanisms are expected to play a critical role in the IPv4-IPv6 transition and coexistence. Due to IPv4 address depletion, it is likely that in the future, many IPv6-only clients will want to connect to IPv4-only servers. In the typical case, the approach only requires the deployment of IPv6/IPv4 translators that connect an IPv6-only network to an IPv4-only network, along with the deployment of one or more DNS64-enabled name servers. However, some features require performing the DNS64 function directly in the end hosts themselves.

This document is structured as follows: Section 2 provides a non-normative overview of the behavior of DNS64. Section 3 provides a non-normative background required to understand the interaction between DNS64 and DNS Security Extensions (DNSSEC). The normative specification of DNS64 is provided in Sections 4, 5, and 6. Section 4 defines the terminology, Section 5 is the actual DNS64 specification, and Section 6 covers deployment issues. Section 7 is non-normative and provides a set of examples and typical deployment scenarios.