IPv6-Only-Preferred Option for DHCP
draft-link-dhc-v6only-01

Document Type Active Internet-Draft (dhc WG)
Last updated 2019-12-24 (latest revision 2019-12-09)
Stream IETF
Intended RFC status Proposed Standard
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Stream WG state Adopted by a WG (wg milestones: Jan 2020 - Adopt IPv6-Only-Pref..., Mar 2020 - WGLC IPv6-Only-Prefe... )
Document shepherd Bernie Volz
IESG IESG state I-D Exists
Consensus Boilerplate Yes
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Send notices to Bernie Volz <volz@cisco.com>
Dynamic Host Configuration                                    L. Colitti
Internet-Draft                                                J. Linkova
Intended status: Standards Track                                  Google
Expires: June 11, 2020                                     M. Richardson
                                                               Sandelman
                                                            T. Mrugalski
                                                                     ISC
                                                        December 9, 2019

                  IPv6-Only-Preferred Option for DHCP
                        draft-link-dhc-v6only-01

Abstract

   This document specifies a DHCP option to indicate that a host
   supports an IPv6-only mode and willing to forgo obtaining an IPv4
   address if the network provides IPv6 connectivity.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 11, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of

Colitti, et al.           Expires June 11, 2020                 [Page 1]
Internet-Draft     IPv6-Only-Preferred Option for DHCP     December 2019

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Reasons to Signal IPv6-Only Support in DHCPv4 Packets . . . .   4
   3.  IPv6-Only Preferred Option  . . . . . . . . . . . . . . . . .   5
     3.1.  Option format . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  DHCPv4 Client Behaviour . . . . . . . . . . . . . . . . .   5
     3.3.  DHCPv4 Server Behaviour . . . . . . . . . . . . . . . . .   7
     3.4.  Configuration Variables . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   One of the biggest challenges of deploying IPv6-only LANs is that
   such networks might contain rather heterogeneous collection of hosts.
   Some of them are capable of operating in IPv6-only mode (either
   because the OS and all applications are IPv6-only capable or because
   the host has some form of 464XLAT [RFC6877] deployed).  At the same
   time some devices might still have IPv4 dependencies and need IPv4
   connectivity to operate properly.  To incrementally rollout
   IPv6-only, network operators need to provide IPv4-as-a-service
   whereby a host receives an IPv4 address if it needs it, while
   IPv6-only capable devices (such as modern mobile devices) are not
   allocated IPv4 addresses.  Deploying separate LAN segments for
   IPv6-only and for dual-stack hosts (such as two WiFi SSIDs or two
   VLANs) is undesirable for a number of reasons, including but not
   limited to:

   o  Doubling the number of network segments which leads to operational
      complexity and performance impact, for instance due to TCAM
      utilization increase from an increased number of ACL entries.

   o  Placing a host into the correct network segment is problematic.
      For example, in the case of 802.11 Wi-Fi the user might select the
      wrong SSID.  In the case of wired 802.1x authentication the
      authentication server might not have all the information required
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