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Internet Engineering Task Force                                 J. Bound
INTERNET DRAFT                                     Compaq Computer Corp.
DHC Working Group                                              M. Carney
Obsoletes:  draft-ietf-dhc-dhcpv6-15.txt           Sun Microsystems, Inc
                                                              C. Perkins
                                                   Nokia Research Center
                                                           R. Droms(ed.)
                                                           Cisco Systems
                                                        22 November 2000


         Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
                      draft-ietf-dhc-dhcpv6-16.txt


Status of This Memo

   This document is a submission by the Dynamic Host Configuration
   Working Group of the Internet Engineering Task Force (IETF). Comments
   should be submitted to the dhcp-v6@bucknell.edu mailing list.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   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."

    The list of current Internet-Drafts can be accessed at:
         http://www.ietf.org/ietf/1id-abstracts.txt
    The list of Internet-Draft Shadow Directories can be accessed at:
         http://www.ietf.org/shadow.html.



Abstract

   The Dynamic Host Configuration Protocol for IPv6 (DHCP) enables
   DHCP servers to pass configuration parameters such as IPv6 network
   addresses to IPv6 nodes.  It offers the capability of automatic
   allocation of reusable network addresses and additional configuration
   flexibility.  This protocol is a stateful counterpart to ``IPv6
   Stateless Address Autoconfiguration'' [14], and can be used






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   separately or concurrently with the latter to obtain configuration
   parameters.


















































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                                Contents


Status of This Memo                                                    i

Abstract                                                               i

 1. Introduction                                                       1

 2. Terminology                                                        2
     2.1. IPv6 Terminology  . . . . . . . . . . . . . . . . . . . .    2
     2.2. DHCP Terminology  . . . . . . . . . . . . . . . . . . . .    3

 3. DHCP Constants                                                     4
     3.1. Multicast Addresses . . . . . . . . . . . . . . . . . . .    5
     3.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . .    5
     3.3. DHCP message types  . . . . . . . . . . . . . . . . . . .    5
     3.4. Error Values  . . . . . . . . . . . . . . . . . . . . . .    7
           3.4.1. Generic Error Values  . . . . . . . . . . . . . .    7
           3.4.2. Server-specific Error Values  . . . . . . . . . .    7
     3.5. Configuration Variables . . . . . . . . . . . . . . . . .    8

 4. Requirements                                                       8

 5. Background                                                         9

 6. Design Goals                                                      10

 7. Non-Goals                                                         11

 8. Overview                                                          11
     8.1. How does a node know to use DHCP? . . . . . . . . . . . .   11
     8.2. How does a client find out about DHCP agents? . . . . . .   11
     8.3. What if the client and server(s) are on different links?    11
     8.4. How does a client request configuration parameters from
             servers? . . . . . . . . . . . . . . . . . . . . . . .   12
     8.5. How do clients and servers identify and manage addresses?   13
     8.6. Can a client release its assigned addresses before the lease
             expires? . . . . . . . . . . . . . . . . . . . . . . .   13
     8.7. What if the client determines one or more of its assigned
             addresses are already being used by another client?  .   13
     8.8. How are clients notified of server configuration changes?   13

 9. Message Formats and Identity Associations                         14
     9.1. DHCP Solicit Message Format . . . . . . . . . . . . . . .   14
     9.2. DHCP Advertise Message Format . . . . . . . . . . . . . .   15
     9.3. DHCP Request Message Format . . . . . . . . . . . . . . .   16



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     9.4. DHCP Reply Message Format . . . . . . . . . . . . . . . .   17
     9.5. DHCP Release Message Format . . . . . . . . . . . . . . .   18
     9.6. DHCP Reconfigure Message Format . . . . . . . . . . . . .   18
     9.7. DHCP Reconfigure-reply Message Format . . . . . . . . . .   18
     9.8. DHCP Reconfigure-init Message Format  . . . . . . . . . .   19
     9.9. Relay-forward message . . . . . . . . . . . . . . . . . .   20
    9.10. Server-forward message  . . . . . . . . . . . . . . . . .   20
    9.11. Identity association  . . . . . . . . . . . . . . . . . .   21

10. DHCP Server Solicitation                                          21
    10.1. Solicit Message Validation  . . . . . . . . . . . . . . .   21
    10.2. Advertise Message Validation  . . . . . . . . . . . . . .   21
    10.3. Client Behavior . . . . . . . . . . . . . . . . . . . . .   22
          10.3.1. Creation and sending of the Solicit message . . .   22
          10.3.2. Time out and retransmission of Solicit Messages .   22
          10.3.3. Receipt of Advertise messages . . . . . . . . . .   23
    10.4. Relay Behavior  . . . . . . . . . . . . . . . . . . . . .   23
          10.4.1. Relaying of Solicit messages  . . . . . . . . . .   23
          10.4.2. Relaying of Advertise messages  . . . . . . . . .   24
    10.5. Server Behavior . . . . . . . . . . . . . . . . . . . . .   24
          10.5.1. Receipt of Solicit messages . . . . . . . . . . .   24
          10.5.2. Creation and sending of Advertise messages  . . .   24

11. DHCP Client-Initiated Configuration Exchange                      25
    11.1. Request Message Validation  . . . . . . . . . . . . . . .   25
    11.2. Reply Message Validation  . . . . . . . . . . . . . . . .   26
    11.3. Release Message Validation  . . . . . . . . . . . . . . .   26
    11.4. Client Behavior . . . . . . . . . . . . . . . . . . . . .   26
          11.4.1. Creation and sending of Request messages  . . . .   27
          11.4.2. Time out and retransmission of Request Messages .   27
          11.4.3. Receipt of Reply message in response to a Request   28
          11.4.4. Creation and sending of Release messages  . . . .   28
          11.4.5. Time out and retransmission of Release Messages .   29
          11.4.6. Receipt of Reply message in response to a Release   29
          11.4.7. When a client should send a Request message . . .   29
          11.4.8. Initialization  . . . . . . . . . . . . . . . . .   29
          11.4.9. Confirming the validity of IPv6 addresses . . . .   29
         11.4.10. Extending the lifetimes on IPv6 addresses . . . .   30
    11.5. Relay Behavior  . . . . . . . . . . . . . . . . . . . . .   31
          11.5.1. Relaying of Request or Release messages . . . . .   31
    11.6. Server Behavior . . . . . . . . . . . . . . . . . . . . .   31
          11.6.1. Receipt of Request messages . . . . . . . . . . .   31
          11.6.2. Receipt of Release messages . . . . . . . . . . .   31
          11.6.3. Creation and sending of Reply messages  . . . . .   32

12. DHCP Server-Initiated Configuration Exchange                      33
    12.1. Reconfigure Message Validation  . . . . . . . . . . . . .   33
    12.2. Reconfigure-reply Message Validation  . . . . . . . . . .   33
    12.3. Reconfigure-init Message Validation . . . . . . . . . . .   33



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    12.4. Server Behavior . . . . . . . . . . . . . . . . . . . . .   33
          12.4.1. Creation and sending of Reconfigure messages  . .   34
          12.4.2. Time out and retransmission of Reconfigure
                          messages . . . . . . . . . . . . . . . . .  34
          12.4.3. Receipt of Reconfigure-reply messages . . . . . .   34
          12.4.4. Creation and sending of Reconfigure-init messages   34
          12.4.5. Time out and retransmission of Reconfigure-init
                          messages . . . . . . . . . . . . . . . . .  35
          12.4.6. Receipt of Request messages . . . . . . . . . . .   35
    12.5. Client Behavior . . . . . . . . . . . . . . . . . . . . .   35
          12.5.1. Receipt of Reconfigure-init messages  . . . . . .   35
          12.5.2. Creation and sending of Request messages  . . . .   36
          12.5.3. Time out and retransmission of Request messages .   36
          12.5.4. Receipt of Reply messages . . . . . . . . . . . .   36

13. Using DHCP for network renumbering                                36

14. DHCP Client Implementor Notes                                     37
    14.1. Primary Interface . . . . . . . . . . . . . . . . . . . .   37
    14.2. Advertise Message and Configuration Parameter Caching . .   37
    14.3. Time out and retransmission variables . . . . . . . . . .   37
    14.4. Server Preference . . . . . . . . . . . . . . . . . . . .   38

15. DHCP Server Implementor Notes                                     38
    15.1. Client Bindings . . . . . . . . . . . . . . . . . . . . .   38
    15.2. Reconfigure-init Considerations . . . . . . . . . . . . .   38
    15.3. Server Preference . . . . . . . . . . . . . . . . . . . .   39
    15.4. Request Message Transaction-ID Cache  . . . . . . . . . .   39

16. DHCP Relay Implementor Notes                                      39

17. Open Issues for Working Group Discussion                          39
    17.1. Authentication  . . . . . . . . . . . . . . . . . . . . .   39
    17.2. DHCP-DNS interaction  . . . . . . . . . . . . . . . . . .   39
    17.3. Release vs.  Decline  . . . . . . . . . . . . . . . . . .   40
    17.4. Request messages  . . . . . . . . . . . . . . . . . . . .   40
    17.5. Use of term ``agent'' . . . . . . . . . . . . . . . . . .   40
    17.6. Use of terms ``subnet'' and ``network'' . . . . . . . . .   40

18. Security                                                          40

19. Year 2000 considerations                                          41

20. IANA Considerations                                               41

21. Acknowledgments                                                   41

22. DHCP options                                                      42
    22.1. Format of DHCP options  . . . . . . . . . . . . . . . . .   42



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    22.2. Identity association option . . . . . . . . . . . . . . .   43
    22.3. Option request option . . . . . . . . . . . . . . . . . .   44
    22.4. Client message option . . . . . . . . . . . . . . . . . .   45
    22.5. Server message option . . . . . . . . . . . . . . . . . .   45
    22.6. Retransmission parameter option . . . . . . . . . . . . .   46
    22.7. Authentication option . . . . . . . . . . . . . . . . . .   46

23. Changes in this draft                                             46
    23.1. Order of sections . . . . . . . . . . . . . . . . . . . .   47
    23.2. Reconfigure message . . . . . . . . . . . . . . . . . . .   47
    23.3. Releasable resources  . . . . . . . . . . . . . . . . . .   47
    23.4. DHCP message header . . . . . . . . . . . . . . . . . . .   47
    23.5. Design goals  . . . . . . . . . . . . . . . . . . . . . .   47
    23.6. Overview  . . . . . . . . . . . . . . . . . . . . . . . .   47
    23.7. Message formats, 9  . . . . . . . . . . . . . . . . . . .   47
    23.8. Solicit and Advertise messages, (section 10)  . . . . . .   48
    23.9. Prefix advertisement  . . . . . . . . . . . . . . . . . .   48
   23.10. Identity Associations . . . . . . . . . . . . . . . . . .   48
   23.11. Extensions renamed options; defined in this document  . .   48
   23.12. Transaction-ID ranges . . . . . . . . . . . . . . . . . .   48
   23.13. Release messages and relays . . . . . . . . . . . . . . .   48
   23.14. Discovering relay agents  . . . . . . . . . . . . . . . .   48

 A. Comparison between DHCPv4 and DHCPv6                              49

 B. Full Copyright Statement                                          51

Chair's Address                                                       54

Author's Address                                                      54






















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1. Introduction

   This document describes DHCP for IPv6 (DHCP), a UDP [13] client
   / server protocol designed to reduce the cost of management of
   IPv6 nodes in environments where network managers require more
   control over the allocation of IPv6 addresses and configuration
   of network stack parameters than that offered by ``IPv6 Stateless
   Autoconfiguration'' [14].  DHCP is a stateful counterpart to
   stateless autoconfiguration.  Note that both stateful and stateless
   autoconfiguration can be used concurrently in the same environment,
   leveraging the strengths of both mechanisms in order to reduce the
   cost of ownership and management of network nodes.

   DHCP reduces the cost of ownership by centralizing the management
   of network resources such as IP addresses, routing information, OS
   installation information, directory service information, and other
   such information on a few DHCP servers, rather than distributing such
   information in local configuration files among each network node.
   DHCP is designed to be easily extended to carry new configuration
   parameters through the addition of new DHCP ``options'' defined to
   carry this information.  (What were called ``extensions'' in the -15
   draft are now called ``options''; see section 23.11.)

   Those readers familiar with DHCP for IPv4 [6] will find DHCP for IPv6
   provides a superset of features, and benefits from the additional
   features of IPv6 and freedom from BOOTP [4]-backward compatibility
   constraints.  For more information about the differences between DHCP
   for IPv6 and DHCP for IPv4, see Appendix A.

   This document is organized as follows.  Section 2 defines terminology
   used throughout this document.  Section 3 defines constant values
   used by DHCP. Section 4 briefly discusses requirement levels.
   Section 5 points the reader to helpful background specifications
   covering related IPv6 protocols.  Section 6 discusses the design
   goals that influenced DHCP. Section 7 identifies some of the
   non-goals of this specification.  Section 8 gives a high level
   overview of DHCP, its message types, and identifies DHCP functional
   entities (client, relay, server).  Section 9 describes in detail
   the format of each DHCP message type.  Section 10 discusses DHCP
   server solicitation.  Section 11 discusses DHCP client-initiated
   configuration information exchange.  Section 12 discusses DHCP
   server-initiated configuration information exchange.  Section 14
   presents helpful notes for DHCP client implementors.  Section 15
   presents helpful notes for DHCP server implementors.  Section 16
   presents helpful notes for DHCP relay implementors.  Section 18
   discusses security considerations for DHCP.

   Section 23 describes the changes between this version of the DHCPv6
   specification and draft-ietf-dhc-dhcpv6-15.txt.



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2. Terminology

2.1. IPv6 Terminology

   IPv6 terminology relevant to this specification from the IPv6
   Protocol [5], IPv6 Addressing Architecture [7], and IPv6 Stateless
   Address Autoconfiguration [14] is included below.

      address    An IP layer identifier for an interface or a set of
                 interfaces.

      unicast address
                 An identifier for a single interface.  A packet sent
                 to a unicast address is delivered to the interface
                 identified by that address.

      multicast address
                 An identifier for a set of interfaces (typically
                 belonging to different nodes).  A packet sent to a
                 multicast address is delivered to all interfaces
                 identified by that address.

      host       Any node that is not a router.

      IP         Internet Protocol Version 6 (IPv6).  The terms IPv4 and
                 IPv6 are used only in contexts where it is necessary to
                 avoid ambiguity.

      interface
                 A node's attachment to a link.

      link       A communication facility or medium over which nodes
                 can communicate at the link layer, i.e., the layer
                 immediately below IP. Examples are Ethernet (simple or
                 bridged); Token Ring; PPP links, X.25, Frame Relay, or
                 ATM networks; and Internet (or higher) layer "tunnels",
                 such as tunnels over IPv4 or IPv6 itself.

      link-layer identifier
                 a link-layer identifier for an interface.  Examples
                 include IEEE 802 addresses for Ethernet or Token Ring
                 network interfaces, and E.164 addresses for ISDN links.

      link-local address
                 An IP address having link-only scope, indicated by
                 having the prefix (FE80::0000/64), that can be used
                 to reach neighboring nodes attached to the same link.
                 Every interface has a link-local address.




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      message    A unit of data carried in a packet, exchanged between
                 DHCP agents and clients.

      neighbor   A node attached to the same link.

      node       A device that implements IP.

      packet     An IP header plus payload.

      prefix     A bit string that consists of some number of initial
                 bits of an address.

      router     A node that forwards IP packets not explicitly
                 addressed to itself.


2.2. DHCP Terminology

   Terminology specific to DHCP can be found below.


      abort status
                 A status value returned to the application that has
                 invoked a DHCP client operation, indicating anything
                 other than success.

      agent address
                 The address of a neighboring DHCP Agent on the same
                 link as the DHCP client.

      binding    A binding (or, client binding) is a group of server
                 data records indexed by <prefix, UUID> containing the
                 server's information about the addresses and other
                 information assigned to the IA.

      DHCP       Dynamic Host Configuration Protocol for IPv6.  The
                 terms DHCPv4 and DHCPv6 are used only in contexts where
                 it is necessary to avoid ambiguity.

      configuration parameter


                 An element of the configuration information set on the
                 server and delivered to the client using DHCP. Such
                 parameters may be used to carry information to be used
                 by a node to configure its network subsystem and enable
                 communication on a link or internetwork, for example.





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      DHCP client (or client)
                 A node that initiates requests on a link to obtain
                 configuration parameters from one or more DHCP servers.

      DHCP domain
                 A chunk of network topology managed by DHCP and
                 operated by a single administrative entity.

      DHCP server (or server)
                 A server is a node that responds to requests from
                 clients, and may or may not be on the same link as the
                 client(s).

      DHCP relay (or relay)
                 A node that acts as an intermediary to deliver DHCP
                 messages between clients and servers, and is on the
                 same link as a client.

      DHCP agent (or agent)
                 Either a DHCP server on the same link as a client, or a
                 DHCP relay.

      Identity association (IA)
                 A collection of addresses assigned to a client.  Each
                 IA has an associated UUID. A server identifies an IA by
                 the tuple (prefix, UUID), where ``prefix'' is a prefix
                 assigned to the link to which the client is attached,
                 An IA may have 0 or more addresses associated with it.

      Releasable resource
                 (Removed; see section 23.3.)

      transaction-ID
                 An unsigned integer to match responses with replies
                 initiated either by a client or server.

      UUID
                 A universally unique identifier for a client.

                 DISCUSSION:

                    Rules for choosing a UUID are TBD.


3. DHCP Constants

   This section describes various program and networking constants used
   by DHCP.




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3.1. Multicast Addresses

   DHCP makes use of the following multicast addresses:

      All DHCP Agents address:  FF02::1:2
                 This link-local multicast address is used by clients to
                 communicate with the on-link agent(s) when they do not
                 know those agents' link-local address(es).  All agents
                 (servers and relays) are members of this multicast
                 group.

      All DHCP Servers address:  FF05::1:3
                 This site-local multicast address is used by clients or
                 relays to communicate with server(s), either because
                 they want to send messages to all servers or because
                 they do not know the server(s) unicast address(es).
                 Note that in order for a client to use this address,
                 it must have an address of sufficient scope to be
                 reachable by the server(s).  All servers within the
                 site are members of this multicast group.


3.2. UDP ports

   DHCP uses the following destination UDP [13] port numbers.  While
   source ports MAY be arbitrary, client implementations SHOULD permit
   their specification through a local configuration parameter to
   facilitate the use of DHCP through firewalls.

      546        Client port.  Used by agents to send messages to
                 clients.  Also used by servers to send messages to
                 relays.

      547        Agent port.  Used by clients to send messages to
                 agents.  Also used by relays to send messages to
                 servers.


3.3. DHCP message types

   DHCP defines the following message types.  More detail on these
   message types can be found in Section 9.  Message types 0 and 9--255
   are reserved and MUST be silently ignored.

      01 DHCP Solicit

         The DHCP Solicit (or Solicit) message is used by clients
         to locate servers.  This message is multicast using the




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         All-DHCP-Agents address.  Relay(s) forward Solicits as
         necessary to off-link servers.

         Section 9.1 contains more details about the Solicit message.

      02 DHCP Advertise

         The DHCP Advertise (or Advertise) message is used by servers
         responding to Solicits.  This message is unicast to the
         client's link-local address (if the server and client are
         on the same link) or unicast to the relay through which the
         Solicit was sent for final delivery to the client.

         Section 9.2 contains more details about the Advertise message.

      03 DHCP Request

         The DHCP Request (or Request) message is used by clients to
         request configuration parameters from servers.  This message is
         multicast using the All-DHCP-Agents address.  Relay(s) forward
         Requests as necessary to off-link servers.

         Section 9.3 contains more details about the Request message.

      04 DHCP Reply

         The DHCP Reply (or Reply) message is used by servers responding
         to Request and Release messages.  In the case of responding to
         a Request message, the Reply contains configuration parameters
         destined for the client.  This message is unicast to the client
         if the client has an address of sufficient scope that is
         reachable by the server.  Otherwise, it is unicast to the relay
         through which the Request or Release message was sent for final
         delivery to the client.

         Section 9.4 contains more details about the Reply message.

      05 DHCP Release

         The DHCP Release (or Release) message is used by clients to
         return one or more IP addresses to servers.  The server will
         acknowledge the receipt of the Release message by sending the
         client a Reply message.

         Section 9.5 contains more details about the Release message.







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      06 DHCP Reconfigure

      07 DHCP Reconfigure-reply

         Removed; see section 23.2.

      08 DHCP Reconfigure-init

         The DHCP Reconfigure-init (or Reconfigure-init) message is set
         by server(s) to inform client(s) that the server(s) has new or
         updated configuration parameters, and that the client(s) are
         to initiate a Request/Reply transaction with the server(s) in
         order to receive the updated information.

         Section 9.8 contains more details about the Reconfigure-init
         message.


3.4. Error Values

   This section describes error values exchanged between DHCP
   implementations.


3.4.1. Generic Error Values

   The following symbolic names are used between client and server
   implementations to convey error conditions.  The following table
   contains the actual numeric values for each name.  Note that the
   numeric values do not start at 1, nor are they consecutive.  The
   errors are organized in logical groups.

   _______________________________________________________________
   |Error_Name___|Error_ID|_Description_________________________|_
   |Success______|00______|_Success_____________________________|_
   |UnspecFail___|16______|_Failure,_reason_unspecified_________|_
   |AuthFailed___|17______|_Authentication_failed_or_nonexistent|_
   |PoorlyFormed_|18______|_Poorly_formed_message_______________|_
   |Unavail______|19______|_Addresses_unavailable_______________|_

3.4.2. Server-specific Error Values

   The following symbolic names are used by server implementations to
   convey error conditions to clients.  The following table contains the
   actual numeric values for each name.







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   _______________________________________________________________
   |Error_Name____|Error_ID|_Description________________________|_
   |NoBinding_____|20______|_Client_record_(binding)_unavailable|_
   |InvalidSource_|21______|_Invalid_Client_IP_address__________|_
   |NoServer______|23______|_Relay_cannot_find_Server_Address___|_
   |ICMPError_____|64______|_Server_unreachable_(ICMP_error)____|_

3.5. Configuration Variables

   This section presents a table of client and server configuration
   variables and the default or initial values for these variables.  The
   client-specific variables MAY be configured on the server and MAY be
   delivered to the client through the ``DHCP Retransmission Parameter
   Option'' in a Reply message.  This option is TBD.

   ______________________________________________________________
   |Parameter__________|Default|_Description___________________|_
   |MIN_SOL_DELAY______|1______|_MIN_(secs)_to_delay_1st_mesg__|_
   |MAX_SOL_DELAY______|5______|_MAX_(secs)_to_delay_1st_mesg__|_
   |ADV_MSG_TIMEOUT____|500____|_SOL_Retrans_timer_(msecs)_____|_
   |ADV_MSG_MAX________|30_____|_MAX_timer_value_(secs)________|_
   |SOL_MAX_ATTEMPTS___|-1_____|_MAX_attempts_(-1_=_infinite)__|_
   |REP_MSG_TIMEOUT____|250____|_REQ_Retrans_timer_(msecs)_____|_
   |REQ_MSG_ATTEMPTS___|10_____|_MAX_Request_attempts__________|_
   |REL_MSG_ATTEMPTS___|5______|_MAX_Release_attempts__________|_
   |RECREP_MSG_TIMEOUT_|2000___|_Retrans_timer_(msecs)_________|_
   |REC_MSG_ATTEMPTS___|10_____|_Reconfigure_attempts__________|_
   |REC_REP_MIN________|5______|_Minimum_pause_interval_(secs)_|_
   |REC_REP_MAX________|7200___|_Maximum_pause_interval_(secs)_|_
   |REC_THRESHOLD______|100____|_%_of_required_clients_________|_
   |SRVR_PREF_WAIT_____|2______|_Advertise_Collect_timer_(secs)|_


4. Requirements

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [2].

   This document also makes use of internal conceptual variables
   to describe protocol behavior and external variables that an
   implementation must allow system administrators to change.  The
   specific variable names, how their values change, and how their
   settings influence protocol behavior are provided to demonstrate
   protocol behavior.  An implementation is not required to have them in
   the exact form described here, so long as its external behavior is
   consistent with that described in this document.





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5. Background

   Related work in IPv6 that would best serve an implementor to study
   is the IPv6 Specification [5], the IPv6 Addressing Architecture [7],
   IPv6 Stateless Address Autoconfiguration [14], IPv6 Neighbor
   Discovery Processing [11], and Dynamic Updates to DNS [16].  These
   specifications enable DHCP to build upon the IPv6 work to provide
   both robust stateful autoconfiguration and autoregistration of DNS
   Host Names.

   The IPv6 Specification provides the base architecture and design of
   IPv6.  A key point for DHCP implementors to understand is that IPv6
   requires that every link in the Internet have an MTU of 1280 octets
   or greater (in IPv4 the requirement is 68 octets).  This means that
   a UDP packet of 536 octets will always pass through an internetwork
   (less 40 octets for the IPv6 header), as long as there are no IP
   options prior to the UDP header in the packet.  But, IPv6 does not
   support fragmentation at routers, so that fragmentation takes place
   end-to-end between hosts.  If a DHCP implementation needs to send a
   packet greater than 1500 octets it can either fragment the UDP packet
   into fragments of 1500 octets or less, or use Path MTU Discovery [9]
   to determine the size of the packet that will traverse a network
   path.

   DHCP clients use Path MTU discovery when they have an address of
   sufficient scope to reach the DHCP server.  If a DHCP client does not
   have such an address, that client MUST fragment its packets if the
   resultant message size is greater than the minimum 1280 octets.

   Path MTU Discovery for IPv6 is supported for both UDP and TCP and
   can cause end-to-end fragmentation when the PMTU changes for a
   destination.

   The IPv6 Addressing Architecture specification [7] defines the
   address scope that can be used in an IPv6 implementation, and the
   various configuration architecture guidelines for network designers
   of the IPv6 address space.  Two advantages of IPv6 are that support
   for multicast is required, and nodes can create link-local addresses
   during initialization.  This means that a client can immediately use
   its link-local address and a well-known multicast address to begin
   communications to discover neighbors on the link.  For instance, a
   client can send a Solicit message and locate a server or relay.

   IPv6 Stateless Address Autoconfiguration [14] (Addrconf) specifies
   procedures by which a node may autoconfigure addresses based on
   router advertisements [11], and the use of a valid lifetime to
   support renumbering of addresses on the Internet.  In addition the
   protocol interaction by which a node begins stateless or stateful
   autoconfiguration is specified.  DHCP is one vehicle to perform



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   stateful autoconfiguration.  Compatibility with addrconf is a design
   requirement of DHCP (see Section 6).

   IPv6 Neighbor Discovery [11] is the node discovery protocol in IPv6
   which replaces and enhances functions of ARP [12].  To understand
   IPv6 and Addrconf it is strongly recommended that implementors
   understand IPv6 Neighbor Discovery.

   Dynamic Updates to DNS [16] is a specification that supports the
   dynamic update of DNS records for both IPv4 and IPv6.  DHCP can use
   the dynamic updates to DNS to integrate addresses and name space
   to not only support autoconfiguration, but also autoregistration
   in IPv6.  The security model to be used with DHCPv6 should conform
   as closely as possible to the authentication model outlined in
   RFC2402 [8].


6. Design Goals

    -  DHCP is a mechanism rather than a policy.  Network administrators
       set their administrative policies through the configuration
       parameters they place upon the DHCP servers in the DHCP domain
       they're managing.  DHCP is simply used to deliver parameters
       according to that policy to each of the DHCP clients within the
       domain.

    -  DHCP is compatible with IPv6 stateless autoconf [14].

    -  DHCP does not require manual configuration of network parameters
       on DHCP clients, except in cases where such configuration is
       needed for security reasons.  A node configuring itself using
       DHCP should require no user intervention.

    -  DHCP does not require a server on each link.  To allow for scale
       and economy, DHCP must work across DHCP relays.

    -  DHCP coexists with statically configured, non-participating nodes
       and with existing network protocol implementations.

    -  DHCP clients can operate on a link without IPv6 routers present.

    -  DHCP will provide the ability to renumber network(s) when
       required by network administrators [3].

    -  A DHCP client can make multiple, different requests for
       configuration parameters when necessary from one or more DHCP
       servers at any time.





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    -  DHCP will contain the appropriate time out and retransmission
       mechanisms to efficiently operate in environments with high
       latency and low bandwidth characteristics.


7. Non-Goals

   This specification explicitly does not cover the following:

    -  Specification of a DHCP server to server protocol.

    -  How a DHCP server stores its DHCP data.

    -  How to manage a DHCP domain or DHCP server.

    -  How a DHCP relay is configured or what sort of information it may
       log.


8. Overview

   This section provides a general overview of the interaction
   between the functional entities of DHCP. The overview is organized
   as a series of questions and answers.  Details of DHCP such
   as message formats and retransmissions are left to sections 9,
   10, 11, 12, 14, 15, and  16.


8.1. How does a node know to use DHCP?

   An unconfigured node determines that it is to use DHCP for
   configuration of an interface by detecting the presence (or absence)
   of routers on the link.  If router(s) are present, the node examines
   router advertisements to determine if DHCP should be used to
   configure the interface.  If there are no routers present, then
   the node MUST use DHCP to configure the interface.  Detail on
   this process can be found in neighbor discovery [11] and stateless
   autoconfiguration [14].


8.2. How does a client find out about DHCP agents?

   (Section removed, see 23.6


8.3. What if the client and server(s) are on different links?

   Use of DHCP in such environments requires one or more DHCP relays
   be set up on the client's link, because a client may only have a



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   link-local address.  Relays receive the Solicit and Request messages
   from the client and forward them to some set of servers within the
   DHCP domain.  The client message is forwarded verbatim as the payload
   in a message from the relay to the server.  A relay will include
   one of its own addresses (of sufficient scope) from the interface
   on the same link as the client, as well as the prefix length of
   that address, in its message to the server.  Servers receiving
   the forwarded traffic use this information to aid in selecting
   configuration parameters appropriate to the client's link.  The
   servers also use the relay's address as the destination to forward
   client-destined messages for final delivery by the relay.

   Relays forward client messages to servers using some combination of
   the FF05::1:3(All Servers) site-local multicast address, some other
   (perhaps a combination) of site-local multicast addresses set up
   within the DHCP domain to include the servers in that domain, or a
   list of unicast addresses for servers.  The network administrator
   makes relay configuration decisions based upon the topological
   requirements (scope) of the DHCP domain they are managing.  Note
   that if the DHCP domain spans more than the site-local scope, then
   the relays MUST be configured with global addresses for the client's
   link so as to be reachable by servers outside the relays' site-local
   environment.


8.4. How does a client request configuration parameters from servers?

   To request configuration parameters, the client forms a Request
   message, and sends it to the server either directly (client has an
   address of sufficient scope) or indirectly (through the on-link
   relay).  The client MAY include a Option Request Option 22.3 (ORO)
   along with other options to request specific information from the
   server.  Note that the client MAY form multiple Request messages
   and send each of them to different servers to request potentially
   different information (perhaps based upon what was advertised) in
   order to satisfy its needs.  As a client's needs may change over time
   (perhaps based upon an application's requirements), the client may
   form additional Request messages to request additional information as
   it is needed.

   The server(s) respond with Reply messages containing the requested
   configuration parameters, which can include status information
   regarding the information requested by the client.  The Reply MAY
   also include additional information, such as a reconfiguration event
   multicast group for the client to join to monitor reconfiguration
   events, as described in section 8.8.






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8.5. How do clients and servers identify and manage addresses?

   Servers and clients manage addresses in groups called ``identity
   associations.''  Each identity associations is identified using
   a unique identifier.  An identity association may contain one or
   more IPv6 addresses.  DHCP servers assign addresses to identity
   associations.  DHCP clients use the addresses in an identity
   association to configure interfaces.  There is always at least one
   identity association per interface that a client wishes to configure.
   Each address in an IA has its own preferred and valid lifetime.  Over
   time, the server may change the characteristics of the addresses in
   an IA; for example, by changing the preferred or valid lifetime for
   an address in the IA. The server may also add or delete addresses
   from an IA; for example, deleting old addresses and adding new
   addresses to renumber a client.  A client can request the current
   list of addresses assigned to an IA from a server through an exchange
   of protocol messages.


8.6. Can a client release its assigned addresses before the lease
   expires?

   A client forms a Release message, including options identifying
   the IA to be released.  The client sends the Release to the server
   which assigned the addresses to the client initially.  If that
   server cannot be reached after a certain number of attempts (see
   section 3.5), the client can abandon the Release attempt.  In this
   case, the address(es) in the IA will be reclaimed by the server(s)
   when the lifetimes on the addresses expire.


8.7. What if the client determines one or more of its assigned addresses
   are already being used by another client?

   If the client determines through a mechanism like Duplicate Address
   Detection [14] that the address it was assigned by the server is
   already in use by another client, the client will form a Release
   message, including the option carrying the in-use address.  The
   option's status field MUST be set to the value reflecting the ``in
   use'' status of the address.


8.8. How are clients notified of server configuration changes?

   There are two possibilities.  Either the clients discover the new
   information when they revisit the server(s) to request additional
   configuration information / extend the lifetime on an address.  or
   through a server-initiated event known as a reconfigure event.




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   The reconfiguration feature of DHCP offers network administrators
   the opportunity to update configuration information on DHCP clients
   whenever necessary.  To signal the need for client reconfiguration,
   the server will unicast a Reconfigure-init message to each
   client individually.  The server may use multicast to signal the
   reconfiguration to multiple clients simultaneously.  (Note that
   there is no mechanism defined in the protocol to guarantee that
   every client actually performs a reconfiguration in response to a
   multicast reconfigure-init message.)  A Reconfigure-init is a trigger
   which will cause the client(s) to initiate a standard Request/Reply
   exchange with the server in order to acquire the new or updated
   addresses.


9. Message Formats and Identity Associations

   All reserved fields in a message MUST be transmitted as zeroes and
   ignored by the receiver of the message.

   DISCUSSION:

      Each DHCP message has an identical fixed format header; some
      messages also allow a variable format area for options.  Not
      all fields in the header are used in every message.  In this
      section, every field is included in every message format
      diagram and fields that are not used in a message are marked
      as ``unused''.  As an alternative, the unused fields could
      be labeled ``unused'' in the format diagram.


9.1. DHCP Solicit Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 1 |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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      preference
                 (unused) MUST be 0

      transaction-ID
                 An unsigned integer generated by the client used to
                 identify this Solicit message.

      client-link-local-address
                 The link-local address of the interface for which the
                 client is using DHCP.

      server-address (unused) MUST be 0


9.2. DHCP Advertise Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 2 |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      preference   An unsigned integer indicating a server's willingness
                   to provide service to the client.

      transaction-ID An unsigned integer used to identify this Advertise
                   message.  Copied from the client's Solicit message.

      client-link-local-address
                   The IP link-local address of the client interface
                   from which the client issued the Solicit message.

      server-address
                   The IP address of the server.  If the DHCP domain




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                   crosses site boundaries, then this address MUST be
                   globally-scoped.

      options      Options are described elsewhere in this document

   See Sections 14.4 and 15.3 for information about how clients and
   servers handle the preference field.


9.3. DHCP Request Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 3 |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      preference
                 (unused) MUST be 0

      transaction-ID
                 An unsigned integer generated by the client used to
                 identify this Request message.

      client-link-local-address
                 The link-local address of the client interface from
                 which the client will issue the Request message.

      server-address
                 The IP address of the server to which the the client's
                 Request message is directed, copied from an Advertise
                 message.

      options
                 Options are described elsewhere in this document.




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9.4. DHCP Reply Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 4 |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                     client-link-local-address                 |
     |                           (16 octets)                         |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      preference An unsigned integer indicating a server's willingness
                 to provide service to the client.

      transaction-ID
                 An unsigned integer used to identify this Reply
                 message.  Copied from the client's Request message.

      client-link-local-address
                 The link-local address of the interface for which the
                 client is using DHCP.

      server-address
                 The IP address of the server.  If the DHCP domain
                 crosses site boundaries, then this address MUST be
                 globally-scoped.

      options
                 Options are described elsewhere in this document.













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9.5. DHCP Release Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 5 | preference    |        transaction-ID         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      preference (unused) MUST be 0

      transaction-ID
                 An unsigned integer generated by the client used to
                 identify this Release message.

      P          (unused) MUST be 0

      client-link-local-address
                 The client's link-local address for the interface from
                 which the client issued the Release message.

      server-address
                 The IP address of the server that assigned the
                 addresses.

      options    See section 22.


9.6. DHCP Reconfigure Message Format

   The Reconfigure message has been deleted (see section 23.2).


9.7. DHCP Reconfigure-reply Message Format

   The Reconfigure-reply message has been deleted (see section 23.2).




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9.8. DHCP Reconfigure-init Message Format

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type = 8 |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                        server-address                         |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      preference (unused) MUST be 0

      transaction-ID
                 An unsigned integer generated by the server to identify
                 this Reconfigure-init message

      client-link-local-address
                 (unused) MUST be 0

      server-address
                 The IP address of the DHCP server issuing the
                 Reconfigure-init message.  MUST be of sufficient scope
                 to be reachable by all clients.

      options    SHOULD only include an ``Options request option''
                 (ORO) and/or authentication options.  No configuration
                 information SHOULD be included.  See section 22 more
                 information about options.













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9.9. Relay-forward message

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type TBD | prefix length |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                                                               |
     |                         relay-address                         |
     |                                                               |
     |                               |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      msg-type   TBD

      prefix-length
                 The length of the prefix in the address in the
                 ``relay-address'' field.

      relay-address
                 An address assigned to the interface through which the
                 message from the client was received.

      options    MUST include a ``Client message option''; see
                 section 22.4.


9.10. Server-forward message

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  msg-type TBD | prefix length |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                                                               |
     |                         relay-address                         |
     |                                                               |
     |                               |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |            options (variable number and length)   ....        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


      msg-type   TBD





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      prefix-length
                 The length of the prefix in the address in the
                 ``relay-address'' field.

      relay-address
                 An address identifying the interface through which the
                 message from the server should be forwarded; copied
                 from the ``client-forward'' message.

      options    MUST include a ``Server message option''; see
                 section 22.5.


9.11. Identity association

   An ``identity-association'' (IA) is a construct through which a
   server and a client can identify, group and manage IPv6 addresses.
   Each IA consists of a UUID and a list of associated IPv6 addresses
   (the list may be empty).  A client associates an IA with one of
   its interfaces and uses the IA to obtain IPv6 addresses for that
   interface from a server.


10. DHCP Server Solicitation

   This section describes how a client locates servers.  The behavior of
   client, server, and relay implementations is discussed, along with
   the messages they use.

   (Prefix advertisements have been deleted; see 23.9.)


10.1. Solicit Message Validation

   Clients MUST silently discard any received Solicit messages.

   Agents MUST silently discard any received Solicit messages if
   the ``client-link-local-address'' field does not contain a valid
   link-local address.


10.2. Advertise Message Validation

   Servers MUST discard any received Advertise messages.

   Clients MUST discard any Advertise messages that meet any of the
   following criteria:





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     o The ``Transaction-ID'' field value does not match the value the
       client used in its Solicit message.

     o The ``client-link-local-address'' field value does not match the
       link-local address of the interface upon which the client sent
       the Solicit message.


10.3. Client Behavior

   Clients use the Solicit message to discover DHCP servers configured
   to serve addresses on the link to which the client is attached.

   (Prefix advertisement by servers has been deleted; see section 23.9.)


10.3.1. Creation and sending of the Solicit message

   The client sets the ``msg-type'' field to 1, and places the
   link-local address of the interface it wishes to configure in the
   ``client-link-local-address'' field.  The client sets all other
   fields to zero.

   The client sends the Solicit message to the FF02::1:2  (All DHCP
   Agents) multicast address, destination port 547.  The source port
   selection can be arbitrary, although it SHOULD be possible using a
   client configuration facility to set a specific source port value.


10.3.2. Time out and retransmission of Solicit Messages

   The client's first Solicit message on the interface MUST be delayed
   by a random amount of time between the interval of MIN_SOL_DELAY and
   MAX_SOL_DELAY. This random delay desynchronizes clients which start
   at the same time (e.g., after a power outage).

   The client waits ADV_MSG_TIMEOUT, collecting Advertise messages.
   If no Advertise messages are received, the client retransmits
   the Solicit, and doubles the ADV_MSG_TIMEOUT value.  This process
   continues until either one or more Advertise messages are received or
   ADV_MSG_TIMEOUT reaches the ADV_MSG_MAX value.  Thereafter, Solicits
   are retransmitted every ADV_MSG_MAX until SOL_MAX_ATTEMPTS have been
   made, at which time the client stops trying to DHCP configure the
   interface.  An event external to DHCP is required to restart the DHCP
   configuration process.

   Default and initial values for MIN_SOL_DELAY, MAX_SOL_DELAY,
   ADV_MSG_TIMEOUT, AND ADV_MSG_MAX are documented in section 3.5.




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10.3.3. Receipt of Advertise messages

   Upon receipt of one or more validated Advertise messages, the client
   selects one or more Advertise messages based upon the following
   criteria.

    -  Those Advertise messages with the highest server preference
       value (see section 14.4) are preferred over all other Advertise
       messages.

    -  Within a group of Advertise messages with the same server
       preference value, a client MAY select those servers whose
       Advertise messages advertise information of interest to
       the client.  For example, one server may be advertising the
       availability of IP addresses which have an address scope of
       interest to the client.

   Once a client has selected Advertise message(s), the client will
   typically store information about each server, such as server
   preference value, addresses advertised, when the advertisement was
   received, and so on.  Depending on the requirements of the client's
   invoking user, the client MAY initiate a configuration exchange with
   the server(s) immediately, or MAY defer this exchange until later.


10.4. Relay Behavior

   For this discussion, the Relay may be configured to use a list of
   server destination addresses, which may include unicast addresses,
   the FF05::1:3 (All DHCP Servers) multicast address, or other
   multicast addresses selected by the network administrator.  If
   the Relay has not been explicitly configured, it will use the
   FF05::1:3 (All DHCP Servers) multicast address as the default.


10.4.1. Relaying of Solicit messages

   When a Relay receives a valid Solicit message, it constructs a
   Relay-forward message.  The client Solicit message is carried as the
   payload of a ``client-message'' option.  The relay places an address
   from the interface on which the Solicit message was received in the
   ``relay-address'' field and the prefix length for that address in
   the ``prefix-length'' field.  The Relay then sends the Relay-forward
   message to the list of server destination addresses that it has been
   configured with.







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10.4.2. Relaying of Advertise messages

   When the relay receives a Relay-reply message, it extracts the server
   message from the ``server-message'' option and forwards the server
   message to the address in the client-link-local-address field in
   the server message.  The relay forwards the server message through
   the interface identified in the ``relay-address'' field in the
   Relay-reply message.


10.5. Server Behavior

   For this discussion, the Server is assumed to have been configured in
   an implementation specific manner.  This configuration is assumed to
   contain all network topology information for the DHCP domain, as well
   as any necessary authentication information.


10.5.1. Receipt of Solicit messages

   If the server receives a Solicit message, the client must be on the
   same link as the server.  If the server receives a Relay-forward
   message containing a Solicit message, the client must be on the
   link to which the prefix identified by the ``relay-address'' and
   ``prefix-length'' fields in the Relay-forward message is assigned.
   The server records the ``relay-address'' field from the Relay-forward
   message and extracts the solicit message from the ``client-message''
   option.

   If administrative policy permits the server to respond to a client on
   that link, the server will generate and send an Advertise message to
   the client.


10.5.2. Creation and sending of Advertise messages

   The server sets the ``msg-type'' field to 2 and copies the values
   of the following fields from the client's Solicit to the Advertise
   message:

     o transaction-ID

     o client-link-local-address

   The server places one of its IP addresses (determined through
   administrator setting) in the ``server-address'' field of the
   Advertise message.  The server sets the ``preference'' field
   according to its configuration information.  See section 15.3 for a
   description of server preference.



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   If the Solicit message was received in a Relay-forward message, the
   server constructs a Relay-reply message with the Advertise message
   in the payload of a ``server-message'' option.  The server unicasts
   the Relay-reply message to the address in the ``relay-address'' field
   from the Relay-forward message.

   If the Solicit message was received directly by the server, the
   server unicasts the Advertise message directly to the client using
   the ``client-link-local-address'' field value as the destination
   address.  The Advertise message MUST be unicast through the interface
   on which the Solicit message was received.

   DISCUSSION:

      (From Ted Lemon) There is a danger in using Solicit versus
      DHCPDISCOVER: in the Solicit paradigm, the client has to
      choose the DHCP server before it knows if the DHCP server
      will give it an IP address, or which addresses the server is
      willing to assign to the client.  It may be that there are
      two or more DHCP servers owned by the same administrative
      domain, and both are theoretically willing to give the
      client addresses, but only one actually has any addresses to
      give.


11. DHCP Client-Initiated Configuration Exchange

   A client uses the Request-Reply message exchange to acquire
   configuration information of interest.  The client may initiate the
   configuration exchange as part of the operating system configuration
   process or when requested to do so by the application layer.

   A client uses the Release-Reply message exchange to indicate to the
   DHCP server that the client will no longer be using the addresses in
   the released IA.


11.1. Request Message Validation

   Clients MUST silently discard any received Request messages.

   Agents MUST discard any Request messages in which the
   ``client-link-local-address'' field does not contain a valid
   link-local address.

   Servers MUST discard any received Request message which meets any of
   the following criteria:





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     o The ``server-address'' field value does not match any of the
       server's addresses.

     o The ``options'' field contains an authentication option, and the
       server cannot successfully authenticate the client.


11.2. Reply Message Validation

   Servers MUST silently discard any received Reply messages.

   Clients MUST discard any Reply message that meets any of the
   following criteria:

     o The ``transaction-ID'' field value does not match the value the
       client used in its Request or Release message.

     o The ``client-link-local-address'' field value does not match the
       link-local address of the interface upon which the client sent in
       its Request or Release message.

     o The Reply message contains an authentication option, and the
       client's attempt to authenticate the message fails.

   Relays MUST discard any Relay-reply message in which the
   ``client-link-local-address'' in the encapsulated Reply message does
   not contain a valid link-local address.


11.3. Release Message Validation

   Clients MUST silently discard any received Release messages.

   Agents MUST discard any Release message in which the
   ``client-link-local-address'' field does not contain a valid
   link-local address.

   Servers MUST discard any received Release message in which the
   ``options'' field contains an authentication option, and the server
   cannot successfully authenticate the client.


11.4. Client Behavior

   A client will generate one or more Request messages to acquire
   configuration information.  A client may initiate such an exchange
   automatically in order to acquire the necessary network parameters
   to communicate with nodes off-link.  The client uses the server
   address information from previous Advertise message(s) for use in



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   constructing Request message(s).  Note that a client may request
   configuration information from one or more servers at any time.

   A client uses the Release message in the management of IAs when:

     o The client has determined through DAD or some other method that
       one or more of the addresses assigned by the server in the IA is
       already in use by a different client.

     o The client has been instructed to release the IA prior to the IA
       expiration time since it is no longer needed.


11.4.1. Creation and sending of Request messages

   The client sets the ``msg-type'' field to 3, and places the
   link-local address of the interface it wishes to acquire
   configuration information for in the ``client-link-local-address''
   field.

   The client generates a transaction ID inserts this value in the
   ``transaction-ID'' field.

   The client places the address of the destination server in the
   ``server-address'' field.

   The client adds any appropriate options, including one or more IA
   options (if the client is requesting that the server assign it some
   network addresses).  If the client does include any IA options,
   it MUST include the list of addresses the client currently has
   associated with that IA. If the client is requesting configuration of
   a new IA, the list of addresses MUST be empty.


11.4.2. Time out and retransmission of Request Messages

   The server will respond to the Request message with a Reply
   message.  If no Reply message is received within REP_MSG_TIMEOUT
   milliseconds, the client retransmits the Request with the same
   transaction-ID, and doubles the REP_MSG_TIMEOUT value, and waits
   again.  The client continues this process until a Reply is received
   or REQUEST_MSG_ATTEMPTS unsuccessful attempts have been made, at
   which time the client MUST abort the configuration attempt.  The
   client SHOULD report the abort status to the application layer.

   Default and initial values for REP_MSG_TIMEOUT and REQ_MSG_ATTEMPTS
   are documented in section 3.5.





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11.4.3. Receipt of Reply message in response to a Request

   Upon the receipt of a valid Reply message, the client extracts the
   configuration information contained in the Reply.  If the ``status''
   field contains a non-zero value, the client reports the error status
   to the application layer.

   The client records the T1 and T2 times for each IA in the Reply
   message.  The client records any addresses included with IAs in
   the Reply message.  The client updates the preferred and valid
   lifetimes for the addresses in the IA from the lifetime information
   in the IA option.  The client leaves any addresses that the client
   has associated with the IA that are not included in the IA option
   unchanged.

   Management of the specific configuration information is detailed in
   the definition of each option, in section 22.


11.4.4. Creation and sending of Release messages

   The client sets the ``msg-type'' field to 5, and places the
   link-local address of the interface associated with the configuration
   information it wishes to release in the ``client-link-local-address''
   field.

   The client generates a transaction ID and places this value in the
   ``transaction-ID'' field.

   The client includes options containing the IAs it is releasing in the
   ``options'' field.  The appropriate ``status'' field in the options
   MUST be set to indicate the reason for the release.

   The client places the IP address of the server that allocated the
   address(es) in the ``server-address'' field.

   If the client is configured to use authentication, the client
   generates the appropriate authentication option, and adds this option
   to the ``options'' field.  Note that the authentication option MUST
   be the last option in the ``options'' field.  See section  22.7 for
   more details about the authentication option.

   (The client always forwards Release messages to the server through a
   relay; see section 11.5.)








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11.4.5. Time out and retransmission of Release Messages

   If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
   the client retransmits the Release, doubles the REP_MSG_TIMEOUT
   value, and waits again.  The client continues this process until a
   Reply is received or REL_MSG_ATTEMPTS unsuccessful attempts have been
   made, at which time the client SHOULD abort the release attempt.
   The client SHOULD return the abort status to the application, if an
   application initiated the release.

   Default and initial values for REP_MSG_TIMEOUT and REL_MSG_ATTEMPTS
   are documented in section 3.5.

   Note that if the client fails to release the IA, the addresses
   assigned to the IA will be reclaimed by the server when the lease
   associated with it expires.


11.4.6. Receipt of Reply message in response to a Release

   Upon receipt of a valid Reply message, the client can consider the
   Release event successful, and SHOULD return the successful status to
   the application layer, if an application initiated the release.


11.4.7. When a client should send a Request message

   The description of the Request/Reply message exchange in this section
   makes no assumptions about the timing or state of the client when
   it initiates a Request/Reply message exchange.  Sections 11.4.8
   through 11.4.10 describe when a client MAY initiate a Request/Reply
   message exchange.  The procedures for timeout and retransmission of
   Request messages are described in section 11.4.2.


11.4.8. Initialization

   If a client has no valid IPv6 addresses of sufficient scope to
   communicate with a DHCP server, it may a Request message to obtain
   new addresses.  The client includes one or more IAs in the Request
   message, to which the server assigns new addresses.  The server then
   returns to IA(s) to the client in a Reply message.


11.4.9. Confirming the validity of IPv6 addresses

   Whenever a client may have moved to a new link, its IPv6 addresses
   may no longer be valid.  Examples of times when a client may have
   moved to a new link include:



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     o The client reboots

     o The client is physically disconnected from a wired connection

     o The client returns from sleep mode

     o The client using a wireless technology changes cells

   In any situation when a client may have moved to a new link, the
   client MUST initiate a Request/Reply message exchange.  The client
   includes any IAs, along with the addresses associated with those IAs,
   in its Request message.  The server returns the IAs with updated list
   of addresses and associated lifetimes.


11.4.10. Extending the lifetimes on IPv6 addresses

   IPv6 addresses assigned to a client through an IA use the same
   preferred and valid lifetimes as IPv6 addresses obtained through
   stateless autoconfiguration.  The server assigns preferred and valid
   lifetimes to the IPv6 addresses it assigns to an IA. To extend those
   lifetimes, the client sends a Request to the server containing an
   ``IA option'' for the IA and its associated addresses.  The server
   determines new lifetimes for the addresses in the IA according to
   the server's administrative configuration.  The server may also add
   new addresses to the IA. The server remove addresses from the IA by
   setting the preferred and valid lifetimes of those addresses to zero.

   The server controls the time at which the client contacts the server
   to extend the lifetimes on assigned addresses through the T1 and
   T2 parameters assigned to an IA. If the server does not assign an
   explicit value to T1 or T2 for an IA, T1 defaults to 0.5 times the
   shortest preferred lifetime of any address assigned to the IA and
   T2 defaults to 0.875 times the shortest preferred lifetime of any
   address assigned to the IA.

   At time T1 for an IA, the client initiates a Request/Reply message
   exchange to extend the lifetimes on any addresses in the IA. The
   client includes an IA option with all addresses currently assigned
   to the IA in its Request message.  The client unicasts this Request
   message to the server that originally assigned the addresses to the
   IA.

   At time T2 for an IA (which will only be reached if the server to
   which the Request message was sent at time T1 has not responded),
   the client initiates a Request/Reply message exchange.  The client
   includes an IA option with all addresses currently assigned to the
   IA in its Request message.  The client multicasts this message to
   the FF02::1:2 (All DHCP Agents) multicast address.



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11.5. Relay Behavior

11.5.1. Relaying of Request or Release messages

   When a Relay receives a valid Request or Release message, it
   constructs a Relay-forward message.  The client message is carried
   as the payload of a ``client-message'' option.  The relay places an
   address from the interface on which the client message was received
   in the ``relay-address'' field and the prefix length for that
   address in the ``prefix-length'' field.  The Relay then forwards the
   Relay-forward message to the list of server destination addresses
   that it has been configured with.


11.6. Server Behavior

   For this discussion, the Server is assumed to have been configured in
   an implementation specific manner with configuration of interest to
   clients.


11.6.1. Receipt of Request messages

   Upon the receipt of a valid Request message from a client the server
   can respond to, (implementation-specific administrative policy
   satisfied) the server scans the options field.

   The server then constructs a Reply message and sends it to the
   client.

   DISCUSSION:

      This section needs text about managing IAs and determining
      options to be returned to client.


11.6.2. Receipt of Release messages

   Upon the receipt of a valid Release message, the server examines the
   IAs and the addresses in the IAs for validity.  If the IAs in the
   message are in a binding for the client and the addresses in the IAs
   have been assigned by the server to those IA, the server deletes
   the addresses from the IAs and makes the addresses available for
   assignment to other clients.

   The server then generates a Reply message.  If all of the IAs were
   valid and the addresses successfully released,, the server sets the
   ``status'' field to ``Success''.  If any of the IAs were invalid or
   if any of the addresses were not successfully released, the server



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   releases none of the addresses in the message and sets the ``status''
   field to ``NoBinding''(section 3.4).

   DISCUSSION:

      What is the behavior of the server relative to a ``partially
      released'' IA; i.e., an IA for which some but not all
      addresses are released?

      Can a client send an empty IA to release all addresses in
      the IA?

      If the IA becomes empty - all addresses are released - can
      the server discard any record of the IA?


11.6.3. Creation and sending of Reply messages

   DISCUSSION:

      XXX - This section needs to be fixed (see section 11.6.1).

   The server sets the ``msg-type'' field to 4 and copies the values
   of the following fields from the client's Request or Release to the
   Reply message:

     o transaction-ID

     o client's link-local address

     o server-address

   The server sets the ``status'' field appropriately (see the table
   in section 3.4) based upon the results of processing the client's
   request.

   If the Request or Release message from the client was originally
   received by the server, the server unicasts the Reply message to the
   link-local address in the ``client-link-local-address'' field.

   If the message was originally received in a Forward-request or
   Forward-release message from a relay, the server places the Reply
   message in the options field of a Response-reply message and unicasts
   the message to the relay's address from the original message.








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12. DHCP Server-Initiated Configuration Exchange

   A server initiates a configuration exchange on behalf of the
   administrator of the DHCP domain.  An administrator may initiate such
   an exchange when new links are added to the domain or existing links
   are to be renumbered.  Other examples include changes in the location
   of directory servers, addition of new services such as printing, and
   availability of new software (system or application).

   DISCUSSION:

      Changed ``networks'' to ``links'' here (ed.).  Why would
      adding new links cause a server-initiated configuration
      exchange?


12.1. Reconfigure Message Validation

   Reconfigure messages have been deleted; see section 23.2.


12.2. Reconfigure-reply Message Validation

   Reconfigure-reply messages have been deleted; see section 23.2.


12.3. Reconfigure-init Message Validation

   Agents MUST silently discard any received Reconfigure-init messages.

   Clients MUST discard any Reconfigure-init messages that do
   not contain an authentication option or that fail the client's
   authentication check.


12.4. Server Behavior

   For this discussion, the server is assumed to have a
   implementation-specific interface by which an administrator
   may initiate a reconfiguration event with some set of clients.

   A server sends a Reconfigure-init message to trigger a client to
   initiate immediately a Request/Reply message exchange with the
   server.  A server can send Reconfigure-init messages only to those
   clients who have an address of sufficient scope to be reachable by
   the server.  Thus, those clients who have not requested an IP address
   and are off-link cannot be reconfigured by the server.

   DISCUSSION:



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      It would be possible to forward Reconfigure-init messages
      through relays if the server records the client's link-local
      address and the relay's address from the client's Request
      message.


12.4.1. Creation and sending of Reconfigure messages

   Reconfigure messages have been deleted; see section 23.2.


12.4.2. Time out and retransmission of Reconfigure messages

12.4.3. Receipt of Reconfigure-reply messages

12.4.4. Creation and sending of Reconfigure-init messages

   The server sets the ``msg-type'' field to 8.  The server generates
   a transaction-ID and inserts it in the ``transaction-ID'' field.
   The server places its address (of appropriate scope) in the
   ``server-address'' field.

   The server MAY include an ORO option to inform the client of what
   information has been changed or new information that has been added.

   The server MUST include an authentication option with the appropriate
   settings and add that option as the last option in the ``options''
   field of the Reconfigure-init message.

   Typically, the server will not provide more than an ORO and / or
   Authentication option, since it will provide the new configuration
   information as part of the Request/Reply transaction triggered by the
   Reconfigure-init message.

   The server may either unicast the Reconfigure-init message to one
   client or multicast the message to one or more Reconfigure Multicast
   Addresses previously sent as options to the clients.  The server
   may unicast Reconfigure-init messages to more than one client
   concurrently; for example, to reliably reconfigure all clients, the
   server will unicast a Reconfigure-init message to each client.

   If the server unicasts to one or more clients, it waits for a Request
   message from those clients confirming that it has received the
   Reconfigure-init and are thus initiating a Request/Reply transaction
   with the server.  The server can determine that a Request message is
   in response to a Reconfigure-init because the transaction-ID in the
   Request will be the same value as was used in the Reconfigure-init
   message.




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   If the server multicasts the Reconfigure-init message, it must use
   some TBD authentication mechanism that can authenticate the server to
   multiple clients.  There is no reliability mechanism for multicast
   Reconfigure-init messages.  A server might use multicast in the
   case where it does not have a list of its clients; for example, a
   server that distributes configuration information to clients using
   stateless autoconfiguration might not keep a list of clients it has
   communicated with.


12.4.5. Time out and retransmission of Reconfigure-init messages

   It the server does not receive a Request message from the client
   in RECREP_MSG_TIMEOUT milliseconds, the server retransmits
   the Reconfigure-init message, doubles the RECREP_MSG_TIMEOUT
   value and waits again.  The server continues this process until
   REC_MSG_ATTEMPTS unsuccessful attempts have been made, at which point
   the server SHOULD abort the reconfigure process.

   Default and initial values for RECREP_MSG_TIMEOUT and
   REC_MSG_ATTEMPTS are documented in section 3.5.


12.4.6. Receipt of Request messages

   The server generates and sends Reply message(s) to the client as
   described in section 11.6.3, including in the ``option'' field new
   values for configuration parameters.


12.5. Client Behavior

   A client MUST always monitor UDP port 546 for Reconfigure-init
   messages on interfaces upon which it has acquired DHCP parameters.
   Since the results of a reconfiguration event may affect application
   layer programs, the client SHOULD log these events, and MAY notify
   these programs of the change through an implementation-specific
   interface.


12.5.1. Receipt of Reconfigure-init messages

   Upon receipt of a valid Reconfigure-init message, the client
   initiates a Request/Reply transaction with the server.








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12.5.2. Creation and sending of Request messages

   When responding to a Reconfigure-init, the client creates and
   sends the Request message in exactly the same manner as outlined in
   section 11.4.1 with the following differences:

      transaction-ID
                The client copies the transaction-ID from the
                Reconfigure-init message into the Request message.

      IAs
                The client includes IA options containing the addresses
                the client currently has assigned to those IAs for the
                interface through which the Reconfigure-init message was
                received.

      Pause before sending Request
                The client pauses before sending the Request for
                a random value within the range REC_REP_MIN and
                REC_REP_MAX seconds.  This delay helps reduce the
                load on the server generated by processing large
                numbers of triggered Request messages from a multicast
                Reconfigure-init message.


12.5.3. Time out and retransmission of Request messages

   The client uses the same variables and retransmission algorithm as it
   does with Request messages generated as part of a client-initiated
   configuration exchange.  See section 11.4.2 for details.


12.5.4. Receipt of Reply messages

   Upon the receipt of a valid Reply message, the client extracts the
   contents of the ``option'' field, and sets (or resets) configuration
   parameters appropriately.  The client records and updates the
   lifetimes for any addresses specified in IAs in the Reply message.
   If the configuration parameters changed were requested by the
   application layer, the client notifies the application layer of the
   changes using an implementation-specific interface.


13. Using DHCP for network renumbering

   This section has been deleted (to be moved to ``Notes about DHCP''
   doc?).





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14. DHCP Client Implementor Notes

   This section provides helpful information for the client implementor
   regarding their implementations.  The text described here is not part
   of the protocol, but rather a discussion of implementation features
   we feel the implementor should consider during implementation.


14.1. Primary Interface

   Since configuration parameters acquired through DHCP can be
   interface-specific or more general, the client implementor SHOULD
   provide a mechanism by which the client implementation can be
   configured to specify which interface is the primary interface.  The
   client SHOULD always query the DHCP data associated with the primary
   interface for non-interface specific configuration parameters.  An
   implementation MAY implement a list of interfaces which would be
   scanned in order to satisfy the general request.  In either case, the
   first interface scanned is considered the primary interface.

   By allowing the specification of a primary interface, the client
   implementor identifies which interface is authoritative for
   non-interface specific parameters, which prevents configuration
   information ambiguity within the client implementation.


14.2. Advertise Message and Configuration Parameter Caching

   If the hardware the client is running on permits it, the implementor
   SHOULD provide a cache for Advertise messages and a cache of
   configuration parameters received through DHCP. Providing these
   caches prevents unnecessary DHCP traffic and the subsequent load
   this generates on the servers.  The implementor SHOULD provide a
   configuration knob for setting the amount of time the cache(s) are
   valid.


14.3. Time out and retransmission variables

   Note that the client time out and retransmission variables outlined
   in section 3.5 can be configured on the server and sent to the client
   through the use of the ``DHCP Retransmission Parameter Option'',
   which is documented in section 22.6.  A client implementation SHOULD
   be able to reset these variables using the values from this option.








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14.4. Server Preference

   A client MUST wait for SRVR_PREF_WAIT seconds after sending a DHCP
   Solicit message to collect Advertise messages and compare their
   preferences (see section 15.3), unless it receives an Advertise
   message with a preference of 255.  If the client receives an
   Advertise message with a preference of 255, then the client MAY act
   immediately on that Advertise without waiting for any more additional
   Advertise messages.


15. DHCP Server Implementor Notes

   This section provides helpful information for the server implementor.


15.1. Client Bindings

   A server implementation MUST use the IA's UUID and the prefix
   specification from which the client sent its Request message(s) as an
   index for finding configuration parameters assigned to the client.
   While it isn't critical to keep track of the other parameters
   assigned to a client, the server MUST keep track of the addresses it
   has assigned to an IA.

   The server should periodically scan its bindings for addresses whose
   leases have expired.  When the server finds expired addresses, it
   MUST delete the assignment of those addresses, thereby making these
   addresses available to other clients.

   The client bindings MUST be stored in non-volatile storage.

   The server implementation should provide policy knobs to control
   whether or not the lifetimes on assigned addresses are renewable, and
   by how long.


15.2. Reconfigure-init Considerations

   A server implementation MUST provide an interface to the
   administrator for initiating reconfigure-init events.

   A server implementation may provide a mechanism for allowing the
   specification of how many clients comprise a reconfigure multicast
   group.  This enables the administrator to control the hit a server
   takes when a reconfigure-init event occurs.






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15.3. Server Preference

   The server implementation SHOULD allow the setting of a server
   preference value by the administrator.  The server preference
   variable is an unsigned single octet value (0--255), with the lowest
   preference being 0 and the highest 255.  Clients will choose higher
   preference servers over those with lower preference values.  If you
   don't choose to implement this feature in your server, you MUST set
   the server preference field to 0 in the Advertise messages generated
   by your server.


15.4. Request Message Transaction-ID Cache

   In order to improve performance, a server implementation MAY include
   an in memory transaction-ID cache.  This cache is indexed by client
   binding and transaction-ID, and enables the server to quickly
   determine whether a Request is a retransmission or a new Request
   without the cost of a database lookup.  If an implementor chooses to
   implement this cache, then they SHOULD provide a configuration knob
   to tune the lifetime of the cache entries.


16. DHCP Relay Implementor Notes

   A relay implementation SHOULD allow the specification of a list of
   destination addresses for forwarded messages.  This list MAY contain
   any mixture of unicast addresses and multicast addresses.

   If a relay receives an ICMP message in response to a DHCP message it
   has forwarded, it SHOULD log this event.


17. Open Issues for Working Group Discussion

   This section contains some items for discussion by the working group.


17.1. Authentication

   Authentication is not discussed in this document.


17.2. DHCP-DNS interaction

   Interaction among DHCP servers, clients and DNS servers is not
   discussed in this document.





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17.3. Release vs.  Decline

   Should there be a separate Decline message through which the client
   informs the server that it has discovered an address that is in use
   by some other host?


17.4. Request messages

   In DHCPv4, there has been much confusion about overloading
   DHCPREQUEST with the actions of initial address allocation
   (INIT), address confirmation (INIT-REBOOT), and extending leases
   (RENEW/REBIND).

   The model for DHCPv6 messages described in section 11 also uses one
   type of message, Request, in each of the scenarios in sections 11.4.8
   through 11.4.10.  The DHCPv6 specification in this document does not
   differentiate the actions taken by a server based on different times
   at which a client might initiate a Request/Reply exchange with a
   server.  That is, the description of server actions in section 11.6.1
   does not differentiate among Requests received from clients based on
   the client behavior described in sections 11.4.8 through 11.4.10.

   It may be necessary to define different server behaviors for each of
   the client scenarios.  For example, in the address-reconfirmation
   scenario (section 11.4.9), servers cannot safely assign new addresses
   to a client.  The reconfirmation Request is broadcast to multiple
   servers, which cannot coordinate the assignment of any addresses.
   Therefore, in this scenario, servers can only acknowledge or deny the
   validity of addresses but cannot allocate any new addresses.


17.5. Use of term ``agent''

   The term ``agent'', taken to mean ``relay agent or server'', may be
   confusing.  ``relay agent or server'' might be clearer.


17.6. Use of terms ``subnet'' and ``network''

   The term ``subnet'' has been eliminated from the document.  The term
   ``network'' is no longer used to describe a link, collection of links
   or collection of IPv6 addresses.


18. Security

   This document references an ``authentication option'' which is TBD.




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   DISCUSSION:

      Based on the discussion of security issues at the
      8/31/00 design team teleconference and subsequent
      DHC WG mailing list discussion, DHCPv6 will use
      the security model from DHCPv4, as described in
      draft-ietf-dhc-authentication-15.txt.


19. Year 2000 considerations

   Since all times are relative to the current time of the transaction,
   there is no problem within the DHCPv6 protocol related to any
   hardcoded dates or two-digit representation of the current year.


20. IANA Considerations

   This document defines message types 1--8 to be received by UDP at
   port numbers 546 and 547.  Additional message types may be defined in
   the future.

   Section 3.1 lists several multicast addresses used by DHCP.

   This document also defines several status codes that are to
   be returned with the Reply and Reconfigure-reply messages (see
   sections 9.4 and 9.7).  The non-zero values for these status codes
   which are currently specified are shown in the table in section 3.4.

   There is a DHCPv6 option described in section 22.6, which allows
   clients and servers to exchange values for some of the timing
   and retransmission parameters defined in section 3.5.  Adding new
   parameters in the future would require extending the values by which
   the parameters are indicated in the DHCP option.  Since there needs
   to be a list kept, the default values for each parameter should also
   be stored as part of the list.

   All of these protocol elements may be specified to assume new values
   at some point in the future.  New values should be approved by the
   process of IETF Consensus [10].


21. Acknowledgments

   Thanks to the DHC Working Group for their time and input into the
   specification.  Ralph Droms and Thomas Narten have had a major
   role in shaping the continued improvement of the protocol by their
   careful reviews.  Many thanks to Matt Crawford, Erik Nordmark, Gerald
   Maguire, and Mike Carney for their studied review as part of the



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   Last Call process.  Thanks also for the consistent input, ideas, and
   review by (in alphabetical order) Brian Carpenter, Jack McCann, Yakov
   Rekhter, Matt Thomas, Sue Thomson, and Phil Wells.

   Thanks to Steve Deering and Bob Hinden, who have consistently
   taken the time to discuss the more complex parts of the IPv6
   specifications.


22. DHCP options

   Options are used to carry additional information and parameters
   in DHCP messages.  Every option shares a common base format, as
   described in section 22.1.

   this document describes the DHCP options defined as part of the base
   DHCP specification.  Other options may be defined in the future in a
   separate document.


22.1. Format of DHCP options

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          option-data                          |
     |                      (option-len octets)                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      option-code
                An unsigned integer identifying the specific option type
                carried in this option.

      option-len
                An unsigned integer giving the length of the data in
                this option in bytes.

      option-data
                The data for the option; the format of this data depends
                on the definition of the option.








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22.2. Identity association option

   The identity association option is used to carry an identity
   association, the parameters associated with the IA and the addresses
   assigned to the IA.

   The format of the IA option is:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              TBD              |            variable           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            IA UUID                            |
     |                          (8 octets)                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              T1                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              T2                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   num-addrs   |              IPv6 address                     |
     +-+-+-+-+-+-+-+-+              (16 octets)                      |
     |                                                               |
     |                                                               |
     +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               |   pref. len   |      preferred lifetime       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | pref. lifetime (cont.)        |        valid lifetime         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | valid lifetime (cont.)        |         IPv6 address          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      option-code
                TBD

      option-len
                Variable; equal to 17 + num-addrs*25

      IA UUID
                The unique identifier for this IA; chosen by the client

      T1        The time at which the client contacts the server from
                which the addresses in the IA were obtained to extend
                the lifetimes of the addresses assigned to the IA.




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      T2        The time at which the client contacts any available
                server to extend the lifetimes of the addresses assigned
                to the IA.

      num-addrs
                An unsigned integer giving the number of addresses
                carried in this IA option (MAY be zero).

      IPv6 address
                An IPv6 address assigned to this IA.

      preferred lifetime
                The preferred lifetime for the associated IPv6 address.

      valid lifetime
                The valid lifetime for the associated IPv6 address.

   The ``IPv6 address'', ``preferred lifetime'' and ``valid lifetime''
   fields are repeated for each address in the IA option (as determined
   by the ``num-addrs'' field).

   DISCUSSION:

      The details of the format and the selection of an IA's UUID
      are TBD.

   DISCUSSION:

      An IA has no explicit ``lifetime'' or ``lease length'' of
      its own.  When the lifetimes of all of the addresses in an
      IA have expired, the IA can be considered as having expired.
      T1 and T2 are included to give servers explicit control over
      when a client recontacts the server about a specific IA.


22.3. Option request option

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    requested-option-code-1    |    requested-option-code-2    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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      option-code TBD.

      option-len
                Variable; equal to twice the number of option codes
                carried in this option.

      option-data
                A list of the option codes for the options requested in
                this option.


22.4. Client message option

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       DHCP client message                     |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      option-code TBD

      option-len
                Variable; equal to the length of the forwarded DHCP
                client message.

      option-data
                The message received from the client; forwarded verbatim
                to the server.


22.5. Server message option

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       DHCP server message                     |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      option-code TBD



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      option-len
                Variable; equal to the length of the forwarded DHCP
                server message.

      option-data
                The message received from the server; forwarded verbatim
                to the client.


22.6. Retransmission parameter option

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          option-data                          |
     |                      (option-len octets)                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      option-code
                An unsigned integer identifying the specific option type
                carried in this option.

      option-len
                An unsigned integer giving the length of the data in
                this option in bytes.

      option-data
                The data for the option; the format of this data depends
                on the definition of the option.


22.7. Authentication option

   The authentication option is TBD.


23. Changes in this draft

   This section describes the changes between this version of the DHCPv6
   specification and draft-ietf-dhc-dhcpv6-15.txt.








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23.1. Order of sections

   New sections have been added at the end of this document to minimize
   changes in section numbering.  Those sections will be rearranged in a
   future revision.


23.2. Reconfigure message

   DHCP Reconfigure and Reconfigure-reply messages and the associated
   mechanisms have been removed from this draft of the specification.


23.3. Releasable resources

   ``Releasable resources'' have been removed from this draft.


23.4. DHCP message header

   A common fixed DHCP message header has been defined.  Not all fields
   are used in all messages.


23.5. Design goals

   The second sentence in the 8th design goal bullet has been removed.


23.6. Overview

   Section 8.2 (DHCP agents) has been removed.  DHCP clients no longer
   need to know about specific DHCP agents.

   Section 8.3 has been modified to reflect the new encapsulating
   mechanism through which relays forward client messages to servers.

   Section 8.6 and 8.7 have been modified to describe ``identity
   associations''.

   Section 8.8 has been modified to reflect the deletion of
   ``reconfigure'' and ``reconfigure-reply'' messages.


23.7. Message formats, 9

   Message formats have been changed.  All messages share a common fixed
   message header followed by options.  The various control bits (``P'',
   ``C'') have been removed from the message header.



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23.8. Solicit and Advertise messages, (section 10)

   The description of the message exchanges have been changed to
   reflect:

    -  New relay behavior - encapsulated client messages

    -  Use of IAs


23.9. Prefix advertisement

   Servers no longer advertise prefixes.


23.10. Identity Associations

   Section 9.11 describes IAs in detail.  A definition of ``IA'' has
   been added to section 2.  The description of messages exchanges
   have been extended to include IAs.  The IA option is defined in
   section 22.2


23.11. Extensions renamed options; defined in this document

   ``extensions'' are now called ``options''; the options referenced in
   this document are defined in section 22.


23.12. Transaction-ID ranges

   Solicit, Advertise, Request, Reply, Release and Reconfigure-init
   messages all use an unsigned 16-bit integer ``Transaction-ID''.
   Transaction-IDs generated by clients are considered to be chosen from
   a different namespace than those chosen by servers.  There is no
   need to restrict clients and servers to select Transaction-IDs from
   specific ranges to avoid conflicts.


23.13. Release messages and relays

   Release/Reply messages are forwarded through relays.  This mechanism
   eliminates the need for an 'R' bit.


23.14. Discovering relay agents

   Clients no longer learn the identity of relay agents.  When the
   client only has a link-local address (e.g., the client has no



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   assigned addresses), it now multicasts Request message, which is then
   forwarded by a relay agent on the same link.


A. Comparison between DHCPv4 and DHCPv6

   This appendix is provided for readers who will find it useful to see
   a model and architecture comparison between DHCPv4 [6, 1] and DHCPv6.
   There are three key reasons for the differences:

     o IPv6 inherently supports a new model and architecture for
       communications and autoconfiguration of addresses.

     o DHCPv6 benefits from the new IPv6 features.

     o New features were added to support the expected evolution and
       the existence of more complicated Internet network service
       requirements.

   IPv6 Architecture/Model Changes:

     o The link-local address permits a node to have an address
       immediately when the node boots, which means all clients have a
       source IP address at all times to locate an on-link server or
       relay.

     o The need for BOOTP compatibility and the broadcast flag have been
       removed.

     o Multicast and address scoping in IPv6 permit the design of
       discovery packets that would inherently define their range by the
       multicast address for the function required.

     o Stateful autoconfiguration has to coexist and integrate with
       stateless autoconfiguration supporting Duplicate Address
       Detection and the two IPv6 lifetimes, to facilitate the dynamic
       renumbering of addresses and the management of those addresses.

     o Multiple addresses per interface are inherently supported in
       IPv6.

     o Some DHCPv4 options are unnecessary now because the configuration
       parameters are either obtained through IPv6 Neighbor Discovery or
       the Service Location protocol [15].

   DHCPv6 Architecture/Model Changes:

     o The message type is the first byte in the packet.




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     o IPv6 Address allocations are now handled in a message option as
       opposed to the message header.

     o Client/Server bindings are now mandatory and take advantage of
       the client's link-local address to always permit communications
       either directly from an on-link server, or from a off-link server
       through an on-link relay.

     o Servers are discovered by a client Solicit, followed by a server
       Advertise message

     o The client will know if the server is on-link or off-link.

     o The on-link relay may locate off-link server addresses from
       system configuration or by the use of a site-wide multicast
       packet.

     o ACKs and NAKs are not used.

     o The server assumes the client receives its responses unless it
       receives a retransmission of the same client request.  This
       permits recovery in the case where the network has faulted.

     o Clients can issue multiple, unrelated Request messages to the
       same or different servers.

     o The function of DHCPINFORM is inherent in the new packet design;
       a client can request configuration parameters other than IPv6
       addresses in the optional option headers.

     o Clients MUST listen to their UDP port for the new Reconfigure
       message from servers.

     o New options have been defined.

   With the changes just enumerated, we can support new user features,
   including

     o Configuration of Dynamic Updates to DNS

     o Address deprecation, for dynamic renumbering.

     o Relays can be preconfigured with server addresses, or use of
       multicast.

     o Authentication

     o Clients can ask for multiple IP addresses.




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     o Addresses can be reclaimed using the Reconfigure-init message.

     o Integration between stateless and stateful address
       autoconfiguration.

     o Enabling relays to locate off-link servers.


B. Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However,
   this document itself may not be modified in any way, such as by
   removing the copyright notice or references to the Internet Society
   or other Internet organizations, except as needed for the purpose
   of developing Internet standards in which case the procedures
   for copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


References

    [1] S. Alexander and R. Droms.  DHCP Options and BOOTP Vendor
        Extensions.  Request for Comments (Draft Standard) 2132,
        Internet Engineering Task Force, March 1997.

    [2] S. Bradner.  Key words for use in RFCs to Indicate Requirement
        Levels.  Request for Comments (Best Current Practice) 2119,
        Internet Engineering Task Force, March 1997.






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    [3] S. Bradner and A. Mankin.  The Recommendation for the IP Next
        Generation Protocol.  Request for Comments (Proposed Standard)
        1752, Internet Engineering Task Force, January 1995.

    [4] W. J. Croft and J. Gilmore.  Bootstrap Protocol.  Request for
        Comments 951, Internet Engineering Task Force, September 1985.

    [5] S. Deering and R. Hinden.  Internet Protocol, Version 6 (IPv6)
        Specification.  Request for Comments (Draft Standard) 2460,
        Internet Engineering Task Force, December 1998.

    [6] R. Droms.  Dynamic Host Configuration Protocol.  Request for
        Comments (Draft Standard) 2131, Internet Engineering Task Force,
        March 1997.

    [7] R. Hinden and S. Deering.  IP Version 6 Addressing Architecture.
        Request for Comments (Proposed Standard) 2373, Internet
        Engineering Task Force, July 1998.

    [8] S. Kent and R. Atkinson.  IP Authentication Header.  Request for
        Comments (Proposed Standard) 2402, Internet Engineering Task
        Force, November 1998.

    [9] J. McCann, S. Deering, and J. Mogul.  Path MTU Discovery for
        IP version 6.  Request for Comments (Proposed Standard) 1981,
        Internet Engineering Task Force, August 1996.

   [10] T. Narten and H. Alvestrand.  Guidelines for Writing an IANA
        Considerations Section in RFCs.  Request for Comments (Best
        Current Practice) 2434, Internet Engineering Task Force, October
        1998.

   [11] T. Narten, E. Nordmark, and W. Simpson.  Neighbor Discovery for
        IP Version 6 (IPv6).  Request for Comments (Draft Standard)
        2461, Internet Engineering Task Force, December 1998.

   [12] D. C. Plummer.  Ethernet Address Resolution Protocol:  Or
        converting network protocol addresses to 48.bit Ethernet address
        for transmission on Ethernet hardware.  Request for Comments
        (Standard) 826, Internet Engineering Task Force, November 1982.

   [13] J. Postel.  User Datagram Protocol.  Request for Comments
        (Standard) 768, Internet Engineering Task Force, August 1980.

   [14] S. Thomson and T. Narten.  IPv6 Stateless Address
        Autoconfiguration.  Request for Comments (Draft Standard) 2462,
        Internet Engineering Task Force, December 1998.





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   [15] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan.  Service
        Location Protocol.  Request for Comments (Proposed Standard)
        2165, Internet Engineering Task Force, June 1997.

   [16] P. Vixie, Ed., S. Thomson, Y. Rekhter, and J. Bound.  Dynamic
        Updates in the Domain Name System (DNS UPDATE).  Request for
        Comments (Proposed Standard) 2136, Internet Engineering Task
        Force, April 1997.












































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Chair's Address

   The working group can be contacted via the current chair:

         Ralph Droms
         Cisco Systems
         300 Apollo Drive
         Chelmsford, MA 01824

         Phone:  (978) 244-4733
         E-mail:  rdroms@cisco.com



Author's Address

   Questions about this memo can be directed to:

        Jim Bound
        Compaq Computer Corporation
        Mail Stop:  ZK03-3/U14
        110 Spitbrook Road
        Nashua, NH 03062
        USA
        Phone:  +1-603-884-0400
        Email:  bound@zk3.dec.com

        Mike Carney
        Sun Microsystems, Inc
        Mail Stop:  UMPK17-202
        901 San Antonio Road
        Palo Alto, CA 94303-4900
        USA
        Phone:  +1-650-786-4171
        Email:  mwc@eng.sun.com

        Charles E. Perkins
        Communications Systems Lab
        Nokia Research Center
        313 Fairchild Drive
        Mountain View, California 94043
        USA
        Phone:  +1-650 625-2986
        EMail:  charliep@iprg.nokia.com
        Fax:  +1 650 625-2502







Bound, Carney, Perkins, Droms (ed.)     Expires 1 May 2001     [Page 54]


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