Dynamic Host Configuration Protocol (DHCP): IPv4 and IPv6 Dual-Stack Issues
RFC 4477

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Network Working Group                                           T. Chown
Request for Comments: 4477                     University of Southampton
Category: Informational                                        S. Venaas
                                                                 UNINETT
                                                               C. Strauf
                                      Clausthal University of Technology
                                                                May 2006

              Dynamic Host Configuration Protocol (DHCP):
                    IPv4 and IPv6 Dual-Stack Issues

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   A node may have support for communications using IPv4 and/or IPv6
   protocols.  Such a node may wish to obtain IPv4 and/or IPv6
   configuration settings via the Dynamic Host Configuration Protocol
   (DHCP).  The original version of DHCP (RFC 2131) designed for IPv4
   has now been complemented by a new DHCPv6 (RFC 3315) for IPv6.  This
   document describes issues identified with dual IP version DHCP
   interactions, the most important aspect of which is how to handle
   potential problems in clients processing configuration information
   received from both DHCPv4 and DHCPv6 servers.  The document makes a
   recommendation on the general strategy on how best to handle such
   issues and identifies future work to be undertaken.

Chown, et al.                Informational                      [Page 1]
RFC 4477                DHCP: Dual-Stack Issues                 May 2006

Table of Contents

   1. Introduction ....................................................3
   2. Configuration Scenarios .........................................3
   3. Dual-Stack Issues ...............................................4
      3.1. Handling Multiple Responses ................................4
      3.2. Different Administrative Management ........................5
      3.3. Multiple Interfaces ........................................5
      3.4. DNS Load Balancing .........................................5
      3.5. DNS Search Path Issues .....................................5
      3.6. Protocol Startup Sequence ..................................6
      3.7. DHCP Option Variations .....................................6
      3.8. Security Issues ............................................6
   4. Potential Solutions .............................................7
      4.1. Separate DHCP Servers ......................................7
      4.2. Single DHCPv6 Server .......................................8
      4.3. Optimising for Failure with Lists of Addresses .............9
      4.4. Administrative and Other Areas ............................10
   5. Summary ........................................................10
   6. Security Considerations ........................................12
   7. Acknowledgements ...............................................12
   8. Informative References .........................................12

Chown, et al.                Informational                      [Page 2]
RFC 4477                DHCP: Dual-Stack Issues                 May 2006

1.  Introduction

   The original specification of the Dynamic Host Configuration Protocol
   (DHCP) was made with only IPv4 in mind.  That specification has been
   subsequently revised, up to the latest version of DHCP [1].  With the
   arrival of IPv6, a new DHCP specification for IPv6 has been designed
   and published as DHCPv6 [4].

   These protocols allow nodes to communicate via IPv4 or IPv6
   (respectively) to retrieve configuration settings for operation in a
   managed environment.  While an IPv6 node may acquire address-related
   configuration settings via IPv6 stateless address autoconfiguration
   [2], such a node may wish to use stateless DHCPv6 [5] for other
   administratively configured options, such as DNS or NTP.

   In early IPv6 deployments, a dual-stack mode of operation is
   typically used.  There will thus be nodes that require both IPv4 and
   IPv6 configuration settings.  This document discusses issues with
   obtaining such settings in a dual-stack environment.

   There is a general multihoming issue to be solved for DHCP.  A host
   might simultaneously be connected to multiple networks managed by
   multiple parties.  Also, IPv4 and IPv6 might be managed by separate
   parties.  While these issues are touched on in this document, here we
   focus on the specific issues for operating DHCP in a mixed (typically
   dual-stack) IPv4 and IPv6 environment within a single administrative
   domain.

   In this document, we refer to a "DHCP server" as a server
   implementing the original DHCP [1], and a "DHCPv6 server" as a server