Discovering PREF64 in Router Advertisements
RFC 8781
Internet Engineering Task Force (IETF) L. Colitti
Request for Comments: 8781 J. Linkova
Category: Standards Track Google
ISSN: 2070-1721 April 2020
Discovering PREF64 in Router Advertisements
Abstract
This document specifies a Neighbor Discovery option to be used in
Router Advertisements (RAs) to communicate prefixes of Network
Address and Protocol Translation from IPv6 clients to IPv4 servers
(NAT64) to hosts.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8781.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
1.1. Requirements Language
1.2. Terminology
2. Use Cases for Communicating the NAT64 Prefix to Hosts
3. Why Include the NAT64 Prefix in Router Advertisements?
4. Option Format
4.1. Scaled Lifetime Processing
5. Usage Guidelines
5.1. Handling Multiple NAT64 Prefixes
5.2. PREF64 Consistency
6. IANA Considerations
7. Security Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
NAT64 [RFC6146] with DNS Extensions for Network Address Translation
from IPv6 clients to IPv4 servers (DNS64) [RFC6147] is a widely
deployed mechanism to provide IPv4 access on IPv6-only networks. In
various scenarios, the host must be aware of the NAT64 prefix in use
by the network. This document specifies a Neighbor Discovery
[RFC4861] option to be used in Router Advertisements (RAs) to
communicate NAT64 prefixes to hosts.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
PREF64 (or NAT64 prefix): An IPv6 prefix used for IPv6 address
synthesis [RFC6146];
NAT64: Network Address and Protocol Translation from IPv6 clients to
IPv4 servers [RFC6146];
Router Advertisement (RA): A message used by IPv6 routers to
advertise their presence together with various link and Internet
parameters [RFC4861];
DNS64: a mechanism for synthesizing AAAA records from A records
[RFC6147];
2. Use Cases for Communicating the NAT64 Prefix to Hosts
On networks employing NAT64, it is useful for hosts to know the NAT64
prefix for several reasons, including the following:
* Enabling DNS64 functions on end hosts. In particular:
- Local DNSSEC validation (DNS64 in stub-resolver mode). As
discussed in [RFC6147], Section 2, the stub resolver in the
host "will try to obtain (real) AAAA RRs, and in case they are
not available, the DNS64 function will synthesize AAAA RRs for
internal usage." Therefore, to perform the DNS64 function, the
stub resolver needs to know the NAT64 prefix. This is required
in order to use DNSSEC on a NAT64 network.
- Trusted DNS server. AAAA synthesis is required for the host to
be able to use a DNS server not provided by the network (e.g.,
a DNS-over-TLS [RFC7858] or DNS-over-HTTPS [RFC8484] server
with which the host has an existing trust relationship).
- Networks with no DNS64 server. Hosts that support AAAA
synthesis and are aware of the NAT64 prefix in use do not need
the network to perform the DNS64 function at all.
* Enabling NAT64 address-translation functions on end hosts. For
example:
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