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Internet Engineering Task Force                                 J. Bound
INTERNET DRAFT                                                     Nokia
DHC Working Group                                              M. Carney
Obsoletes:  draft-ietf-dhc-dhcpv6-16.txt           Sun Microsystems, Inc
                                                              C. Perkins
                                                   Nokia Research Center
                                                           R. Droms(ed.)
                                                           Cisco Systems
                                                            1 March 2001


         Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
                      draft-ietf-dhc-dhcpv6-17.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" [13], and can be used 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. Requirements                                                       1

 3. Background                                                         1

 4. Design Goals                                                       3

 5. Non-Goals                                                          3

 6. Terminology                                                        4
     6.1. IPv6 Terminology  . . . . . . . . . . . . . . . . . . . .    4
     6.2. DHCP Terminology  . . . . . . . . . . . . . . . . . . . .    5

 7. DHCP Constants                                                     6
     7.1. Multicast Addresses . . . . . . . . . . . . . . . . . . .    7
     7.2. UDP ports . . . . . . . . . . . . . . . . . . . . . . . .    7
     7.3. DHCP message types  . . . . . . . . . . . . . . . . . . .    7
     7.4. Error Values  . . . . . . . . . . . . . . . . . . . . . .    9
           7.4.1. Generic Error Values  . . . . . . . . . . . . . .    9
           7.4.2. Server-specific Error Values  . . . . . . . . . .    9
     7.5. Configuration Variables . . . . . . . . . . . . . . . . .   10

 8. Overview                                                          10
     8.1. How does a node know to use DHCP? . . . . . . . . . . . .   10
     8.2. What if the client and server(s) are on different links?    10
     8.3. How does a client request configuration parameters from
             servers? . . . . . . . . . . . . . . . . . . . . . . .   11
     8.4. How do clients and servers identify and manage addresses?   11
     8.5. Can a client release its assigned addresses before the lease
             expires? . . . . . . . . . . . . . . . . . . . . . . .   12
     8.6. What if the client determines one or more of its assigned
             addresses are already being used by another client?  .   12
     8.7. How are clients notified of server configuration changes?   12

 9. Message Formats                                                   13
     9.1. DHCP Solicit Message Format . . . . . . . . . . . . . . .   13
     9.2. DHCP Advertise Message Format . . . . . . . . . . . . . .   14
     9.3. DHCP Request Message Format . . . . . . . . . . . . . . .   14
     9.4. DHCP Confirm Message Format . . . . . . . . . . . . . . .   14
     9.5. DHCP Renew Message Format . . . . . . . . . . . . . . . .   15
     9.6. DHCP Rebind Message Format  . . . . . . . . . . . . . . .   15
     9.7. DHCP Reply Message Format . . . . . . . . . . . . . . . .   16
     9.8. DHCP Release Message Format . . . . . . . . . . . . . . .   16



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     9.9. DHCP Decline Message Format . . . . . . . . . . . . . . .   16
    9.10. DHCP Reconfigure-init Message Format  . . . . . . . . . .   17

10. Relay messages                                                    17
    10.1. Relay-forward message . . . . . . . . . . . . . . . . . .   17
    10.2. Relay-reply message . . . . . . . . . . . . . . . . . . .   18

11. Identity association                                              18

12. DHCP Server Solicitation                                          19
    12.1. Solicit Message Validation  . . . . . . . . . . . . . . .   19
    12.2. Advertise Message Validation  . . . . . . . . . . . . . .   19
    12.3. Client Behavior . . . . . . . . . . . . . . . . . . . . .   19
          12.3.1. Creation and sending of the Solicit message . . .   19
          12.3.2. Time out and retransmission of Solicit Messages .   20
          12.3.3. Receipt of Advertise messages . . . . . . . . . .   20
    12.4. Server Behavior . . . . . . . . . . . . . . . . . . . . .   21
          12.4.1. Receipt of Solicit messages . . . . . . . . . . .   21
          12.4.2. Creation and sending of Advertise messages  . . .   21

13. DHCP Client-Initiated Configuration Exchange                      22
    13.1. Client Message Validation . . . . . . . . . . . . . . . .   22
    13.2. Server Message Validation . . . . . . . . . . . . . . . .   23
    13.3. Client Behavior . . . . . . . . . . . . . . . . . . . . .   23
          13.3.1. Creation and sending of Request messages  . . . .   24
          13.3.2. Creation and sending of Confirm messages  . . . .   24
          13.3.3. Creation and sending of Renew messages  . . . . .   26
          13.3.4. Creation and sending of Rebind messages . . . . .   27
          13.3.5. Receipt of Reply message in response to a Reply,
                          Confirm, Renew or Rebind message . . . . .  28
          13.3.6. Creation and sending of Release messages  . . . .   29
          13.3.7. Time out and retransmission of Release Messages .   29
          13.3.8. Creation and sending of Decline messages  . . . .   30
          13.3.9. Time out and retransmission of Decline Messages .   30
         13.3.10. Receipt of Reply message in response to a Release
                          message  . . . . . . . . . . . . . . . . .  31
    13.4. Server Behavior . . . . . . . . . . . . . . . . . . . . .   31
          13.4.1. Receipt of Request messages . . . . . . . . . . .   31
          13.4.2. Receipt of Confirm messages . . . . . . . . . . .   32
          13.4.3. Receipt of Renew messages . . . . . . . . . . . .   32
          13.4.4. Receipt of Rebind messages  . . . . . . . . . . .   33
          13.4.5. Receipt of Release messages . . . . . . . . . . .   34
          13.4.6. Sending of Reply messages . . . . . . . . . . . .   35

14. DHCP Server-Initiated Configuration Exchange                      35
    14.1. Reconfigure-init Message Validation . . . . . . . . . . .   35
    14.2. Server Behavior . . . . . . . . . . . . . . . . . . . . .   35
          14.2.1. Creation and sending of Reconfigure-init messages   36
          14.2.2. Time out and retransmission of unicast
                          Reconfigure-init messages  . . . . . . . .  37
          14.2.3. Time out and retransmission of multicast
                          Reconfigure-init messages  . . . . . . . .  37
          14.2.4. Receipt of Request messages . . . . . . . . . . .   37



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    14.3. Client Behavior . . . . . . . . . . . . . . . . . . . . .   37
          14.3.1. Receipt of Reconfigure-init messages  . . . . . .   37
          14.3.2. Creation and sending of Request messages  . . . .   38
          14.3.3. Time out and retransmission of Request messages .   38
          14.3.4. Receipt of Reply messages . . . . . . . . . . . .   38

15. Relay Behavior                                                    38
    15.1. Relaying of Solicit messages  . . . . . . . . . . . . . .   39
    15.2. Relaying of Advertise messages  . . . . . . . . . . . . .   39

16. DHCP options                                                      39
    16.1. Format of DHCP options  . . . . . . . . . . . . . . . . .   40
    16.2. Identity association option . . . . . . . . . . . . . . .   40
    16.3. Option request option . . . . . . . . . . . . . . . . . .   42
    16.4. Client message option . . . . . . . . . . . . . . . . . .   43
    16.5. Server message option . . . . . . . . . . . . . . . . . .   43
    16.6. Retransmission parameter option . . . . . . . . . . . . .   44
    16.7. Authentication option . . . . . . . . . . . . . . . . . .   44
    16.8. Reconfigure-delay option  . . . . . . . . . . . . . . . .   44
    16.9. DSTM Global IPv4 Address Option . . . . . . . . . . . . .   44

17. DHCP Client Implementor Notes                                     45
    17.1. Primary Interface . . . . . . . . . . . . . . . . . . . .   45
    17.2. Advertise Message and Configuration Parameter Caching . .   46
    17.3. Time out and retransmission variables . . . . . . . . . .   46
    17.4. Server Preference . . . . . . . . . . . . . . . . . . . .   46

18. DHCP Server Implementor Notes                                     46
    18.1. Client Bindings . . . . . . . . . . . . . . . . . . . . .   46
    18.2. Reconfigure-init Considerations . . . . . . . . . . . . .   47
          18.2.1. Reliable transmission of multicast Reconfigure-init
                          messages . . . . . . . . . . . . . . . . .  47
    18.3. Server Preference . . . . . . . . . . . . . . . . . . . .   47
    18.4. Request Message Transaction-ID Cache  . . . . . . . . . .   47

19. DHCP Relay Implementor Notes                                      48

20. Open Issues for Working Group Discussion                          48
    20.1. Authentication  . . . . . . . . . . . . . . . . . . . . .   48
    20.2. Identification of IAs by servers  . . . . . . . . . . . .   48
    20.3. DHCP-DNS interaction  . . . . . . . . . . . . . . . . . .   48
    20.4. Anonymous addresses . . . . . . . . . . . . . . . . . . .   48
    20.5. Use of term "agent" . . . . . . . . . . . . . . . . . . .   48
    20.6. Client behavior when response to Rebind is not received .   49
    20.7. Additional options  . . . . . . . . . . . . . . . . . . .   49
    20.8. Operational parameters  . . . . . . . . . . . . . . . . .   49

21. Security                                                          49

22. Year 2000 considerations                                          49

23. IANA Considerations                                               49




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24. Acknowledgments                                                   50

 A. Comparison between DHCPv4 and DHCPv6                              50

 B. Full Copyright Statement                                          52

 C. Changes in this draft                                             53
     C.1. New messages for confirming addresses and extending the lease
             on an IA . . . . . . . . . . . . . . . . . . . . . . .   53
     C.2. New message formats . . . . . . . . . . . . . . . . . . .   53
     C.3. Renamed Server-forward message  . . . . . . . . . . . . .   53
     C.4. Clarified relay forwarding of messages  . . . . . . . . .   53
     C.5. Addresses and options in Advertise messages . . . . . . .   53
     C.6. Clarification of IA option format . . . . . . . . . . . .   53
     C.7. Specification of transaction ID in Solicit message  . . .   54
     C.8. Edits to definitions  . . . . . . . . . . . . . . . . . .   54
     C.9. Relay agent messages  . . . . . . . . . . . . . . . . . .   54
    C.10. Relay agent behavior  . . . . . . . . . . . . . . . . . .   54
    C.11. Transmission of all client messages through relays  . . .   54
    C.12. Reconfigure-init messages . . . . . . . . . . . . . . . .   54
    C.13. Ordering of sections  . . . . . . . . . . . . . . . . . .   54
    C.14. DSTM option . . . . . . . . . . . . . . . . . . . . . . .   54

Chair's Address                                                       57

Author's Address                                                      57






























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1. Introduction

   This document describes DHCP for IPv6 (DHCP), a UDP [12]
   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" [13].  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.

   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.


2. 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.


3. 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 [13], IPv6 Neighbor
   Discovery Processing [10], and Dynamic Updates to DNS [15].  These
   specifications enable DHCP to build upon the IPv6 work to provide




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   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 [8]
   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 [13] (Addrconf) specifies
   procedures by which a node may autoconfigure addresses based on
   router advertisements [10], 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
   stateful autoconfiguration.  Compatibility with addrconf is a design
   requirement of DHCP (see Section 4).

   IPv6 Neighbor Discovery [10] is the node discovery protocol in IPv6
   which replaces and enhances functions of ARP [11].  To understand
   IPv6 and Addrconf it is strongly recommended that implementors
   understand IPv6 Neighbor Discovery.

   Dynamic Updates to DNS [15] 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



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   not only support autoconfiguration, but also autoregistration in
   IPv6.


4. 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 [13].

    -  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.

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


5. 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.




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6. Terminology

6.1. IPv6 Terminology

   IPv6 terminology relevant to this specification from the IPv6
   Protocol [5], IPv6 Addressing Architecture [7], and IPv6 Stateless
   Address Autoconfiguration [13] 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                  The initial bits of an address, or a set
                              of IP address that share the same initial
                              bits.

      prefix length           The number of bits in a prefix.

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


6.2. 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 containing
                                the server's information about the
                                addresses in an IA and any other
                                configuration information assigned to
                                the client.  A binding is indexed by the
                                tuple <prefix, DUID>, where the 'prefix'
                                is a prefix assigned to the link to
                                which the client is attached and 'DUID'
                                is the DUID from the IA in the binding.

                                DISCUSSION:

                                   The indexing of an IA by <prefix,
                                   DUID> is still under discussion.

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




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      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.

      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 set of links 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.

      DUID                      A DHCP unique identifier for a client.

                                DISCUSSION:

                                   Rules for choosing a DUID are TBD.

      Identity association (IA) A collection of addresses assigned to
                                a client.  Each IA has an associated
                                DUID. An IA may have 0 or more addresses
                                associated with it.

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


7. DHCP Constants

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






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7.1. Multicast Addresses

   DHCP makes use of the following multicast addresses:

      All DHCP Agents address:  FF02::1:2 This link-scoped 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-scoped 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.

   DISCUSSION:

      Is there a requirement for a site-scoped "All DHCP Clients"
      multicast address, to be used as the default in sending
      Reconfigure messages.


7.2. UDP ports

   DHCP uses the following destination UDP [12] 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 servers as the destination port
                 for messages sent to clients and relays.  Used by relay
                 agents as the destination port for messages sent to
                 clients.

      547        Agent port.  Used as the destination port by clients
                 for messages sent to agents.  Used as the destination
                 port by relays for messages sent to servers.


7.3. 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
   TBD--255 are reserved and MUST be silently ignored.  The message code
   for each message type is shown with the message name.

      TBD DHCP Solicit            The DHCP Solicit (or Solicit) message
                                  is used by clients to locate servers.



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      TBD DHCP Advertise          The DHCP Advertise (or Advertise)
                                  message is used by servers responding
                                  to Solicits.

      TBD DHCP Request            The DHCP Request (or Request)
                                  message is used by clients to request
                                  configuration parameters from servers.

      TBD DHCP Confirm            The DHCP Confirm (or Confirm) message
                                  is used by clients to confirm that
                                  the addresses assigned to an IA and
                                  the lifetimes for those addresses,
                                  as well as the current configuration
                                  parameters assigned by the server to
                                  the client are still valid.

      TBD DHCP Renew              The DHCP Renew (or Renew) message
                                  is used by clients to obtain the
                                  addresses assigned to an IA and the
                                  lifetimes for those addresses, as
                                  well as the current configuration
                                  parameters assigned by the server to
                                  the client.  A client sends a Renew
                                  message to the server that originally
                                  assigned the IA when the lease on an
                                  IA is about to expire.

      TBD DHCP Rebind             The DHCP Rebind (or Rebind) message
                                  is used by clients to obtain the
                                  addresses assigned to an IA and the
                                  lifetimes for those addresses, as
                                  well as the current configuration
                                  parameters assigned by the server to
                                  the client.  A clients sends a Rebind
                                  message to all available DHCP servers
                                  when the lease on an IA is about to
                                  expire.

      TBD DHCP Reply              The DHCP Reply (or Reply) message is
                                  used by servers responding to Request,
                                  Confirm, Renew, Rebind, Release and
                                  Decline messages.  In the case of
                                  responding to a Request, Confirm,
                                  Renew or Rebind message, the Reply
                                  contains configuration parameters
                                  destined for the client.

      TBD DHCP Release            The DHCP Release (or Release) message
                                  is used by clients to return one or
                                  more IP addresses to servers.

      TBD DHCP Decline            The DHCP Decline (or Decline) message
                                  is used by clients to indicate that



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                                  the client has determined that one or
                                  more addresses in an IA are already in
                                  use on the link to which the client is
                                  connected.

      TBD 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.


7.4. Error Values

   This section describes error values exchanged between DHCP
   implementations.


7.4.1. 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_______________|_

7.4.2. 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.
   _______________________________________________________________
   |Error_Name____|Error_ID|_Description________________________|_
   |NoBinding_____|20______|_Client_record_(binding)_unavailable|_
   |ConfNoMatch___|21______|_Client_record_Confirm_not_match_IA_|_

   |RenwNoMatch___|22______|_Client_record_Renew_not_match_IA___|_
   |RebdNoMatch___|23______|_Client_record_Rebind_not_match_IA__|_
   |InvalidSource_|24______|_Invalid_Client_IP_address__________|_
   |NoServer______|25______|_Relay_cannot_find_Server_Address___|_
   |ICMPError_____|64______|_Server_unreachable_(ICMP_error)____|_



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7.5. 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.

   _________________________________________________________________________
   |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____|_Retrans_timer_(msecs)_for_Reply__________|_
   |QRY_MSG_ATTEMPTS___|10_____|_MAX_Request/Confirm/Renew/Rebind_attempts|_
   |REL_MSG_ATTEMPTS___|5______|_MAX_Release/Decline_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)___________|_


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 can be found in later sections of this
   document.


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 [10] and stateless
   autoconfiguration [13].


8.2. 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
   link-local address.  Relays receive the Solicit and Request messages
   from the client and forward them to some set of servers within the



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   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 All DHCP 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.


8.3. 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 16.3 (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 8.7.


8.4. 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



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   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.


8.5. 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 7.5), 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.


8.6. 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 [13] 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.


8.7. 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.

   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




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   exchange with the server in order to acquire the new or updated
   addresses.


9. Message Formats

   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 described for every message and fields that are not used in a
   message are marked as "unused".  All unused fields in a message MUST
   be transmitted as zeroes and ignored by the receiver of the message.

   The DHCP message header:

      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   |  preference   |         transaction-ID        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   client-link-local-address                   |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         server-address                        |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                                                               .
     .                            options                            .
     |                          (variable)                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




9.1. DHCP Solicit Message Format

      msg-type                    TBD

      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



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      options                     See section 16.


9.2. DHCP Advertise Message Format

      msg-type                    TBD

      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 that
                                  generated this message.  If the DHCP
                                  domain crosses site boundaries, then
                                  this address MUST be globally-scoped.

      options                     See section 16.


9.3. DHCP Request Message Format

      msg-type                    TBD

      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 this message is directed, copied
                                  from an Advertise message.

      options                     See section 16.


9.4. DHCP Confirm Message Format

      msg-type                    TBD

      preference                  (unused) MUST be 0



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

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

      server-address              MUST be zero.

      options                     See section 16.


9.5. DHCP Renew Message Format

      msg-type                    TBD

      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
                                  this Renew message is directed, which
                                  MUST be the address of the server from
                                  which the IAs in this message were
                                  originally assigned.

      options                     See section 16.


9.6. DHCP Rebind Message Format

      msg-type                    TBD

      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              MUST be zero.

      options                     See section 16.



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9.7. DHCP Reply Message Format

      msg-type                    TBD

      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                     See section 16.


9.8. DHCP Release Message Format

      msg-type                    TBD

      preference                  (unused) MUST be 0

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

      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 16.


9.9. DHCP Decline Message Format

      msg-type                    TBD

      preference                  (unused) MUST be 0

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



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      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 16.


9.10. DHCP Reconfigure-init Message Format

      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                     See section 16.


10. Relay messages

   Relay agents exchange messages with servers to forward messages
   between clients and servers that are not connected to the same link.


10.1. 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   | 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 assigned to the interface through which
                      the message from the client was received.

      options         MUST include a "Client message option"; see
                      section 16.4.


10.2. Relay-reply 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   | 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 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 16.5.


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 DUID 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.

   See section 16.2 for the representation of an IA in a DHCP message.







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12. 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.


12.1. 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.


12.2. Advertise Message Validation

   Servers MUST discard any received Advertise messages.

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

     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.


12.3. Client Behavior

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


12.3.1. Creation and sending of the Solicit message

   The client sets the "msg-type" field to TBD, and places the
   link-local address of the interface it wishes to configure in the
   "client-link-local-address" field.

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

   The client MAY include an Option Request Option in the Solicit
   message.  The client MUST NOT include any other options except those
   specifically allowed as defined by specific options.

   The client sends the Solicit message to the All DHCP Agents
   multicast address, destination port 547.  The source port selection




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   can be arbitrary, although it SHOULD be possible using a client
   configuration facility to set a specific source port value.


12.3.2. 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 7.5.


12.3.3. 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 17.4) 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.

   If the client needs to select an alternate server in the case that a
   chosen server does not respond, the client choose the server with the
   next highest preference value.




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   The client MAY choose a less-preferred server if that server has a
   better set of advertised parameters.


12.4. 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.


12.4.1. 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.


12.4.2. Creation and sending of Advertise messages

   The server sets the "msg-type" field to TBD 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 18.3 for a description of
   server preference.

   The server MUST include options to the Advertise message containing
   any addresses that would be assigned to IAs contained in the Solicit
   message from the client.  The server MAY include other options the
   server will return to the client in a subsequent Reply message.
   The information in these options will be used by the client in the
   selection of a server if the client receives more than one Advertise
   message.





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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.


13. DHCP Client-Initiated Configuration Exchange

   A client initiates a message exchange with the server to acquire
   or update 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.

   The client uses the following messages to initiate a configuration
   event with the server:

      Request   Obtain initial configuration information when the client
                has no assigned addresses

      Confirm   Confirm the validity of assigned addresses and other
                configuration changes when the client's assigned
                addresses may not be valid; for example, when the client
                reboots or loses its connection to a link

      Renew     Extend the lease on an IA through the server that
                originally assigned the IA

      Rebind    Extend the lease on an IA through any server willing to
                extend the lease

   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.

   A client uses the Decline-Reply message exchange to indicate to the
   DHCP server that the client has detected that one or more addresses
   assigned by the server is already in use on the client's link.


13.1. Client Message Validation

   Clients MUST silently discard any received client messages (Request,
   Confirm, Renew, Rebind, Release or Decline messages).





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

   Servers MUST discard any received client messages in which the
   "options" field contains an authentication option, and the server
   cannot successfully authenticate the client.

   Servers MUST discard any received Request or Renew message in which
   the "server-address" field value does not match any of the server's
   addresses.


13.2. Server Message Validation

   Servers MUST silently discard any received server messages (Reply
   messages).

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

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

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

     o The server 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.


13.3. Client Behavior

   A client will use Request, Confirm, Renew and Rebind messages to
   acquire and confirm the validity of 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 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
   the client has been instructed to release the IA prior to the IA
   expiration time since it is no longer needed.





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   A client uses the Decline message when 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.


13.3.1. Creation and sending of Request messages

   If a client has no valid IPv6 addresses of sufficient scope to
   communicate with a DHCP server, it may send 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.

   The client sets the "msg-type" field to TBD, 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).  The list of addresses in each included IA MUST
   be empty.

   The client sends the Request message to the 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.

   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 7.5.


13.3.2. Creation and sending of Confirm messages

   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 Confirm/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.

   The client sets the "msg-type" field to TBD, 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 sets the "server-address" field to 0.

   The client adds any appropriate options, including one or more IA
   options (if the client is requesting that the server confirm the
   validity of 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.

   The client sends the Confirm message to the 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.

   Servers will respond to the Confirm message with a Reply message.  If
   no Confirm message is received within REP_MSG_TIMEOUT milliseconds,
   the client retransmits the Confirm 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 QRY_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 QRY_MSG_ATTEMPTS
   are documented in section 7.5.

   If the client receives no response to its Confirm message, it MAY
   restart the configuration process by locating a different DHCP server
   with an Advertise message and sending a Request to that server, as
   described in section 13.3.1.





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13.3.3. Creation and sending of Renew messages

   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.

   The client sets the "msg-type" field to TBD, 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 extend the lease
   on some IAs; note that the client may check the status of other
   configuration parameters without asking for lease extensions).  If
   the client does include any IA options, it MUST include the list of
   addresses the client currently has associated with that IA.

   The client sends the Renew message to the 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.

   The server will respond to the Renew message with a Reply message.
   If no Reply message is received within REP_MSG_TIMEOUT milliseconds,



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   the client retransmits the Renew 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 until time T2 is
   reached (see section 13.3.4).

   Default and initial values for REP_MSG_TIMEOUT are documented in
   section 7.5.


13.3.4. Creation and sending of Rebind messages

   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
   All DHCP Agents multicast address.

   The client sets the "msg-type" field to TBD, 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 sets the "server-address" field to 0.

   The client adds any appropriate options, including one or more IA
   options.  If the client does include any IA options (if the client is
   requesting that the server extend the lease on some IAs; note that
   the client may check the status of other configuration parameters
   without asking for lease extensions), it MUST include the list of
   addresses the client currently has associated with that IA.

   The client sends the Rebind message to the 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.

   The server will respond to the Rebind message with a Reply message.
   If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
   the client retransmits the Rebind 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.

   Default and initial values for REP_MSG_TIMEOUT are documented in
   section 7.5.

   DISCUSSION:

      The client has several alternatives to choose from if it
      receives no response to its Rebind message.



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       -  When the lease on the IA expires, the client may choose
          to use a Solicit message to locate a new DHCP server and
          send a Request for the expired IA to the new server

       -  Some addresses in the IA may have lifetimes that extend
          beyond the lease of the IA, so the client may choose
          to continue to use those addresses; once all of the
          addresses have expired, the client may choose to locate
          a new DHCP server

       -  The client may have other addresses in other IAs, so the
          client may choose to discard the expired IA and use the
          addresses in the other IAs


13.3.5. Receipt of Reply message in response to a Reply, Confirm, Renew
   or Rebind message

   Upon the receipt of a valid Reply, Confirm, Renew or Rebind 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 16.

   When the client receives an Unavail error status in an IA from the
   server for a Request message the client will have to find a new
   server to create an IA Association.

   When the client receives a NoBinding error status in an IA from the
   server for a Confirm message the client can assume it needs to send a
   Request to reestablish an IA Association with the server.

   When the client receives a Conf_NoMatch error status in an IA from
   the server for a Confirm message the client can send a Renew message
   to the server to extend the lease for the addresses.

   When the client receives a NoBinding error status in an IA from the
   server for a Renew message the client can assume it needs to send a
   Request to reestablish an IA Association with the server.

   When the client receives a Renw_NoMatch error status in an IA from
   the server for a Renew message the client can assume it needs to send
   a Request to reestablish an IA Association with the server.



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   When the client receives an Unavail error status in an IA from the
   server for a Renew message the client can assume it needs to send a
   Request to reestablish an IA Association set of addresses with the
   server.

   When the client receives a NoBinding error status in an IA from the
   server for a Rebind message the client can assume it needs to send
   a Request to reestablish an IA Association with the server or try
   another server.

   When the client receives a Rebd_NoMatch error status in an IA from
   the server for a Rebind message the client can assume it needs to
   send a Request to reestablish an IA Association with the server or
   try another server.

   When the client receives an Unavail error status in an IA from the
   server for a Rebind message the client can assume it needs to send a
   Request to reestablish an IA Association set of addresses with the
   server or try another server.


13.3.6. Creation and sending of Release messages

   The client sets the "msg-type" field to TBD, 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 places the IP address of the server that allocated the
   address(es) in the "server-address" 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.

   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  16.7 for more
   details about the authentication option.


13.3.7. 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.




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   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 7.5.

   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.


13.3.8. Creation and sending of Decline messages

   The client sets the "msg-type" field to TBD, and places the
   link-local address of the interface associated with the configuration
   information it wishes to decline in the "client-link-local-address"
   field.

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

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

   The client includes options containing the IAs it is declining in the
   "options" field.  The appropriate "status" field in the options MUST
   be set to indicate the reason for declining the address.

   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  16.7 for more
   details about the authentication option.


13.3.9. Time out and retransmission of Decline Messages

   If no Reply message is received within REP_MSG_TIMEOUT milliseconds,
   the client retransmits the Decline, 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 attempt to
   decline the address.  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 7.5.









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13.3.10. Receipt of Reply message in response to a Release message

   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.


13.4. Server Behavior

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


13.4.1. 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.

   The server SHOULD process each option for the client in an
   implementation-specific manner.  The server MUST construct a Reply
   message containing the following values:

      msg-type                    TBD

      preference                  Enter the servers preference to
                                  provide services to the client.

      transaction-ID              Enter the transaction-ID from the
                                  Request message.

      client-link-local address   Enter the client-link-local address
                                  from the Request message.

      server address              Enter the IP address of the server.

   When the server receives a Request and IA option is included the
   client is requesting the configuration of a new IA by the server.
   The server MUST take the clients IA and associate a binding for
   that client in an implementation-specific manner within the servers
   configuration parameter database for DHCP clients.

   If the server cannot provide addresses to the client it SHOULD send
   back an empty IA to the client with the status field set to Unavail.

   If the server can provide addresses to the client it MUST send back
   the IA to the client with all fields entered and a status of Success,
   and add the IA as a new client binding.




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13.4.2. Receipt of Confirm messages

   Upon the receipt of a valid Confirm 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.

   The server SHOULD process each option for the client in an
   implementation-specific manner.  The server MUST construct a Reply
   message containing the following values:

      msg-type                    TBD

      preference                  Enter the servers preference to
                                  provide services to the client.

      transaction-ID              Enter the transaction-ID from the
                                  Confirm message.

      client-link-local address   Enter the client-link-local address
                                  from the Confirm message.

      server address              Enter the server's address.

   When the server receives a Confirm and an IA option is included the
   client is requesting confirmation that the addresses in the IA are
   valid.  The server SHOULD locate the clients binding and verify the
   information in the IA from the client matches the information stored
   for that client.

   If the server cannot find a client entry for this IA the server
   SHOULD return an empty IA with status set to NoBinding.

   If the server finds that the information for the client does not
   match what is in the servers records for that client the server
   should send back an empty IA with status set to Conf_NoMatch.

   If the server finds a match to the Confirm then the server should
   send back the IA to the client with status set to success.


13.4.3. Receipt of Renew messages

   Upon the receipt of a valid Renew 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.





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   The server SHOULD process each option for the client in an
   implementation-specific manner.  The server MUST construct a Reply
   message containing the following values:

      msg-type                    TBD

      preference                  Enter the servers preference to
                                  provide services to the client.

      transaction-ID              Enter the transaction-ID from the
                                  Confirm message.

      client-link-local address   Enter the client-link-local address
                                  from the Confirm message.

      server address              Enter the server's address.

   When the server receives a Renew and IA option from a client it
   SHOULD locate the clients binding and verify the information in the
   IA from the client matches the information stored for that client.

   If the server cannot find a client entry for this IA the server
   SHOULD return an empty IA with status set to NoBinding.

   If the server finds that the addresses in the IA for the client do
   not match the clients binding the server should return an empty IA
   with status set to Renw_NoMatch.

   If the server cannot Renew addresses for the client it SHOULD send
   back an empty IA to the client with the status field set to Unavail.

   If the server finds the addresses in the IA for the client then the
   server SHOULD send back the IA to the client with new lease times
   and T1/T2 times if the default is not being used, and set status to
   Success.


13.4.4. Receipt of Rebind messages

   Upon the receipt of a valid Rebind 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.

   The server SHOULD process each option for the client in an
   implementation-specific manner.  The server MUST construct a Reply
   message containing the following values:

      msg-type                    TBD





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      preference                  Enter the servers preference to
                                  provide services to the client.

      transaction-ID              Enter the transaction-ID from the
                                  Confirm message.

      client-link-local address   Enter the client-link-local address
                                  from the Confirm message.

      server address              Enter the server's address.

   When the server receives a Renew and IA option from a client it
   SHOULD locate the clients binding and verify the information in the
   IA from the client matches the information stored for that client.

   If the server cannot find a client entry for this IA the server
   SHOULD return an empty IA with status set to NoBinding.

   If the server finds that the addresses in the IA for the client do
   not match the clients binding the server should return an empty IA
   with status set to Rebd_NoMatch.

   If the server cannot Rebind addresses for the client it SHOULD send
   back an empty IA to the client with the status field set to Unavail.

   If the server finds the addresses in the IA for the client then the
   server SHOULD send back the IA to the client with new lease times
   and T1/T2 times if the default is not being used, and set status to
   Success.


13.4.5. 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
   releases none of the addresses in the message and sets the "status"
   field to "NoBinding"(section 7.4).

   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?




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      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?


13.4.6. Sending of Reply messages

   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.


14. DHCP Server-Initiated Configuration Exchange

   A server initiates a configuration exchange to force DHCP clients
   to obtain new addresses and other configuration information.  For
   example, an administrator may use a server-initiated configuration
   exchange when links in the DHCP domain 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).


14.1. 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.

   Clients MUST discard any Reconfigure-init messages that contain a
   transaction-ID that matches the transaction-ID in a Reconfigure-init
   message previously received from the same DHCP server.


14.2. Server Behavior

   A server sends a Reconfigure-init message to trigger a client to
   initiate immediately a Request/Reply message exchange with the
   server.  A server may unicast a Reconfigure-init message directly
   to a single client or use multicast to deliver a Reconfigure-init
   message to multiple clients.






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14.2.1. Creation and sending of Reconfigure-init messages

   The server sets the "msg-type" field to TBD. 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.

   The server MAY include a Reconfigure-delay option in a
   Reconfigure-init message to be unicast to a client, and MUST
   include a Reconfigure-delay option in a Reconfigure-init message to
   be multicast to a group of clients.

   The server MUST NOT include any other options in the Reconfigure-init
   except as specifically allowed in the definition of individual
   options.

   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.

   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.

   DISCUSSION:

      Authentication of multicast reconfigure-init is still an
      open issue.





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   See section 18.2 for recommendations on the use of multicast
   and unicast Reconfigure-init messages for reliable client
   reconfiguration.


14.2.2. Time out and retransmission of unicast Reconfigure-init messages

   If 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 7.5.


14.2.3. Time out and retransmission of multicast Reconfigure-init
   messages

   After the server transmits the initial Reconfigure-init message,
   the server waits RECREP_MSG_TIMEOUT milliseconds.  The server
   then retransmits the Reconfigure-init message, doubles the
   RECREP_MSG_TIMEOUT value and waits again.  The server repeats this
   process until a total of REC_MSG_ATTEMPTS Reconfigure-init messages
   have been transmitted.

   Default and initial values for RECREP_MSG_TIMEOUT and
   REC_MSG_ATTEMPTS are documented in section 7.5.


14.2.4. Receipt of Request messages

   The server generates and sends Reply message(s) to the client as
   described in section 13.4.6, including in the "option" field new
   values for configuration parameters.


14.3. 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.


14.3.1. 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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14.3.2. 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 13.3.1 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.


14.3.3. 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 13.3.1 for details.


14.3.4. 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.


15. Relay Behavior

   For this discussion, the Relay may be configured to use a list of
   server destination addresses, which may include unicast addresses,
   the All DHCP Servers multicast address, or other multicast addresses
   selected by the network administrator.  If the Relay has not been



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   explicitly configured, it will use the All DHCP Servers multicast
   address as the default.


15.1. Relaying of Solicit messages

   When a Relay receives a valid Solicit message, it constructs
   a Relay-forward message.  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.  This address will be used by the server to
   identify the link to which the client is connected and will be used
   by the relay to forward the Advertise message from the server back to
   the client.

   The relay constructs a "relay-message" option 16.4 that contains
   the entire Solicit message from the client in the data field of the
   option.  The relay places the "relay-message" option along with any
   "relay-specific" options in the options field of the Relay-forward
   message.  The Relay then sends the Relay-forward message to the list
   of server destination addresses that it has been configured with.


15.2. Relaying of Advertise messages

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


16. 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 16.1.

   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.














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16.1. 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.


16.2. 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:


























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      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              |          option-len           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            IA DUID                            |
     |                          (8 octets)                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              T1                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              T2                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   IA status   |   num-addrs   |  addr status  | prefix length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                         IPv6 address                          |
     |                          (16 octets)                          |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      preferred lifetime                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        valid lifetime                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  addr status  | prefix length |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
     |                         IPv6 address                          |
     |                          (16 octets)                          |
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |      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 DUID   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.

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



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      IA status Status of the IA in this option.

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

      addr status Status of this address.

      prefix length Prefix length for this address.

      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 DUID
      are TBD.

   Note that 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.


16.3. 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    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              ...                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      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.



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16.4. 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.


16.5. 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

      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.














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16.6. 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.


16.7. Authentication option

   The authentication option is TBD.


16.8. Reconfigure-delay option

   The Reconfigure-delay option specifies the amount of time a client
   should delay before sending a Request message in response to a
   Reconfigure-init 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   minimum delay time (msec)   |   maximum delay time (msec)   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   The client chooses a random number between the minimum delay time and
   the maximum delay time and delays that number of milliseconds before
   sending its Request message.


16.9. DSTM Global IPv4 Address Option

   The DSTM Global IPv4 Address Option informs a client or server that
   the Identity Association Option (IA) following this option will



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   contain an IPv4-Mapped IPv6 Address [?] in the case of a Client
   receiving the option, or is a Request for an IPv4-Mapped IPv6 Address
   from a client in the case of a DHCPv6 Server receiving the option.
   The option can also provide an IPv6 address to be used as the Tunnel
   Endpoint (TEP) to encapsulate an IPv4 packet within IPv6.

   This option can be used with the Request, Reply, and Reconfigure-Init
   Messages for cases where a server wants to assign to clients
   IPv4-Mapped IPv6 Addresses, thru the Option Request Option (ORO).

    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-length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Tunnel End Point (TEP)               |
   |                           (If Present)                        |
   |                            (16 octets)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:            TBD
   option-length:          Variable: 0 or 16
   Tunnel End Point:       IPv6 Address if Present


   A DSTM IPv4 Global Address Option MUST only apply to the IA following
   this option.


17. 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.


17.1. 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.



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17.2. 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.


17.3. Time out and retransmission variables

   Note that the client time out and retransmission variables outlined
   in section 7.5 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 16.6.  A client implementation SHOULD be
   able to reset these variables using the values from this option.


17.4. 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 18.3), 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.


18. DHCP Server Implementor Notes

   This section provides helpful information for the server implementor.


18.1. Client Bindings

   A server implementation MUST use the IA's DUID 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.





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


18.2. 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 processing load
   impact of the multicast of a Reconfigure-init message.


18.2.1. Reliable transmission of multicast Reconfigure-init messages

   Because clients will ignore Reconfigure-init messages with the
   same transaction-ID, a server can retransmit a Reconfigure-init
   message (using the same transaction-ID) without causing any
   client to reply more than once.  A server SHOULD retransmit a
   multicast Reconfigure-init message several times to maximize the
   probability that all clients in the multicast group have received the
   Reconfigure-init message.

   If a server does not receive a Reply message from some clients in a
   multicast group, the server MAY choose to unicast a Reconfigure-init
   message to those clients.  Because the clients may have received the
   multicast Reconfigure-init messages while the server did not receive
   the clients' Reply messages, the server SHOULD use a different
   transaction-ID in the unicast Reconfigure-init messages to trigger
   the client to reconfigure.


18.3. 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.


18.4. 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



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   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.


19. 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.


20. Open Issues for Working Group Discussion

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


20.1. Authentication

   Authentication is not discussed in this document.  Authentication
   will be modeled on DHCPv4 authentication.  Authentication of
   multicast Reconfigure-init messages is a special problem.


20.2. Identification of IAs by servers

   Do servers identify an IA just by its DUID or by <prefix, DUID>?  If
   just by DUID, are DUIDs guaranteed unique (within the DHCP universe)?
   If so, how is that guarantee implemented?


20.3. DHCP-DNS interaction

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


20.4. Anonymous addresses

   How does DHCPv6 interact with anonymous addresses?  If the server
   assigns anonymous addresses (e.g., addresses with short lifetimes),
   how can a client application choose an anonymous address as a source
   address in preference to a non-anonymous address?


20.5. Use of term "agent"

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




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20.6. Client behavior when response to Rebind is not received

   Section 13.3.4 describes several plausible ways in which a client
   might respond when it does not receive a Reply to a Rebind message.
   The acceptable client behaviors need to be defined and described
   in 13.3.4.


20.7. Additional options

   Which additional options should be included in this base spec
   document?


20.8. Operational parameters

   Should servers have an option to set operational parameters -
   retransmission timeouts, number of retries - in clients?


21. Security

   This document references an "authentication option" which is TBD.

   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.


22. 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.


23. IANA Considerations

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

   Section 7.1 lists several multicast addresses used by DHCP.

   This document also defines several status codes that are to be
   returned with the Reply message (see section 9.7).  The non-zero
   values for these status codes which are currently specified are shown
   in the table in section 7.4.




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   There is a DHCPv6 option described in section 16.6, which allows
   clients and servers to exchange values for some of the timing
   and retransmission parameters defined in section 7.5.  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 [9].


24. 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
   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.


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.



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     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 [14].

   DHCPv6 Architecture/Model Changes:

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

     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.




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     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.

     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 (2001).  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.





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C. Changes in this draft

   This section describes the changes between this version of the DHCPv6
   specification and draft-ietf-dhc-dhcpv6-16.txt.


C.1. New messages for confirming addresses and extending the lease on an
   IA

   Four new messages, DHCP Confirm, DHCP Renew, DHCP Rebind and DHCP
   Decline, have been added and are described in section 13.  Client
   behavior - when and how to send these new messages - and server
   behavior - how to respond to each - has been defined.  The message
   type codes for these messages have been added to section 7.3.


C.2. New message formats

   Section 9 has been restructured to include only one copy of the DHCP
   message header, because now all the messages have the same header
   format.  Descriptions of the use of header fields in the Confirm,
   Renew, Rebind and Decline messages have been added to 9.


C.3. Renamed Server-forward message

   Section 10.2 has been renamed "relay-reply" for consistency with the
   rest of the document


C.4. Clarified relay forwarding of messages

   Added text to sections on relay behavior to clarify encapsulation and
   decapsulation of client messages in Relay-forward and Relay-reply
   messages.


C.5. Addresses and options in Advertise messages

   Modified section 12.4.2 so that servers include addresses to be
   assigned and other options in Advertise messages.  Also added text to
   section 12.3.1 to disallow option values (except as noted in option
   definitions) in Solicit messages.


C.6. Clarification of IA option format

   Changed the label of the prefix length field in an IA option to
   "prefix length" in the option format diagram, and moved the prefix
   before the address for consistency with relay messages and other IPv6
   protocols.





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C.7. Specification of transaction ID in Solicit message

   Add text (which was missing) to specify the insertion of a
   transaction ID in Solicit messages.


C.8. Edits to definitions

   Some of the definitions in section 6 have been edited for clarity.


C.9. Relay agent messages

   The formats of relay agent messages are now described in a separate
   section, 10.


C.10. Relay agent behavior

   The behavior of relay agents for all client and server messages is
   now described in a single section, 15.


C.11. Transmission of all client messages through relays

   All client messages are now multicast to the All Agents multicast
   address and forwarded by relays as appropriate.


C.12. Reconfigure-init messages

   Client behavior in response to a Reconfigure-init messages has
   been extended to accommodate receipt of multiple copies of a
   Reconfigure-init message due to duplicate messages or retransmission.

   Server use of multicast Reconfigure-init has been specified.

   Hints about use of multicast and unicast for reliable reconfiguration
   have been added to server implementor's hints.


C.13. Ordering of sections

   Several sections have been re-ordered for clarity.


C.14. DSTM option

   The DSTM option has been added (section 16.9).







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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.

    [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] 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.

    [9] 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.

   [10] 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.

   [11] 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.

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

   [13] 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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   [14] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan.  Service
        Location Protocol.  Request for Comments (Proposed Standard)
        2165, Internet Engineering Task Force, June 1997.

   [15] 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
        Nokia Networks
        5 Wayside Road
        Burlington, MA 01803
        USA
        Phone:  +1-781-492-6010
        Email:  jim.bound@nokia.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












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