1. Introduction

   This document specifies the way in which Dynamic Host Configuration
   Protocol Version 4 [RFC2131] clients should identify themselves.
   DHCPv4 client implementations that conform to this specification use
   a DHCP Unique Identifier (DUID) as specified in Dynamic Host
   Configuration Protocol for IPv6 (DHCPv6) [RFC3315].  The DUID is
   encapsulated in a DHCPv4 client identifier option, as described in
   "DHCP Options and BOOTP Vendor Extensions" [RFC2132].  The behaviour
   described here supersedes the behavior specified in RFC2131draft and
   RFC2132draft.

   The reason for making this change is that as we make the transition
   from IPv4 to IPv6, there will be network devices that must use both
   DHCPv4 and DHCPv6.  Users of these devices will have a smoother
   network experience if the devices identify themselves consistently,
   regardless of the version of DHCP they are using at any given moment.
   Most obviously, DNS updates made by the DHCP server on behalf of the
   client will be handled more correctly.  This change also addresses
   certain limitations in the functioning of RFC 2131draft/2132-style DHCP
   client identifiers.

   This document first describes the problem to be solved.  It then
   states the new technique that is to be used to solve the problem.
   Finally, it describes the specific changes that one would have to
   make to RFC 2131draft and RFC 2132draft in order for those documents not to
   contradict what is described in this document.