Dynamic Host Configuration working group           Baiju V. Patel,
   Internet Draft                                      Intel Corp,
                                                       Munil Shah
                                                       Microsoft Corp.
   September 16,
   November 20, 1997

             Multicast address allocation extensions to the

                  Dynamic Host Configuration Protocol
                     <draft-ietf-dhc-mdhcp-02.txt>

                     <draft-ietf-dhc-mdhcp-03.txt>

   Status of this Memo

   This document is an Internet Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
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   A revised version of this draft document will be submitted to the
   RFC editor as a Proposed Standard for the Internet Community.
   Discussion and suggestions for improvement are requested.  This
   document will expire before February 1998. Distribution of this
   draft is unlimited.

   Abstract

   The Dynamic Host Configuration Protocol (DHCP) provides a framework
   for passing configuration information to hosts on a TCP/IP network.
   The multicast extensions to DHCP add additional capability of
   dynamic allocation of the multicast addresses and additional
   configuration options.

   1.  Introduction

   The multicast extensions to DHCP (MDHCP) provide configuration
   parameters to the multicast applications.  MDHCP is built on a
   client-server model, where designated DHCP server allocate allocates
   multicast addresses and deliver delivers parameters associated with the                                MDHCP                    09/16/97
   address to dynamically configured hosts.  Throughout the remainder

   Patel and Shah                                                    1
                                MDHCP                    11/20/97

   of this document, the term "server" refers to a host providing
   multicast address(es) and parameters through DHCP, and the term
   "client" refers to a host requesting multicast address(es) and
   parameters from a DHCP server. MDHCP server is used at times, to
   indicate a DHCP server capable of handling MDHCP extensions to the
   DHCP protocol and the MDHCP client is used to indicate the MDHCP
   capable DHCP client. MDHCP is not a separate protocol, but is
   simply extensions an extension to the DHCP protocol.

   MDHCP supports two mechanisms for multicast address allocation.  In

   "automatic allocation", MDHCP assigns a permanent multicast address
   to a client.  In "dynamic allocation", MDHCP assigns a multicast
   address to a client for a limited period of time (or until the
   client explicitly relinquishes the address).  In "manual
   allocation", a client's IP address is assigned by the network
   administrator, and DHCP is used simply to convey the assigned
   address to the client.  A particular network will use one or more

   of these mechanisms, depending on the policies of the network
   administrator.

   Like DHCP, MDHCP should be a mechanism rather than a policy.  MDHCP
   must allow local system administrators control over configuration
   parameters where desired; e.g., local system administrators should
   be able to enforce local policies concerning allocation and access
   to local resources where desired.

   The MDHCP client is not required to obtain IP address from a DHCP
   server in order to use MDHCP protocol.

   The design goals specified in the DHCP RFC also apply to MDHCP.

  1.1. Requirements

   Throughout this document, the words that are used to define the
   significance of particular requirements are capitalized.  These
   words are:

         o "MUST"

           This word or the adjective "REQUIRED" means that the
           item is an absolute requirement of this specification.

         o "MUST NOT"                                MDHCP                    09/16/97

           This phrase means that the item is an absolute prohibition
           of this specification.

         o "SHOULD"

           This word or the adjective "RECOMMENDED" means that there
           may exist valid reasons in particular circumstances to
           ignore this item, but the full implications should be
           understood and the case carefully weighed before choosing a
           different course.

         o "SHOULD NOT"

           This phrase means that there may exist valid reasons in
           particular circumstances when the listed behavior is
           acceptable or even useful, but the full implications should

    Patel and Shah                                               2
                                MDHCP                    11/20/97

           be understood and the case carefully weighed before
           implementing any behavior described with this label.

         o "MAY"

           This word or the adjective "OPTIONAL" means that this item
           is truly optional.  One vendor may choose to include the
           item because a particular marketplace requires it or because
           it enhances the product, for example; another vendor may
           omit the same item.

  1.2. Terminology

      This document uses the following terms[1]:

         o "DHCP client"

           A DHCP client is an Internet host using DHCP to obtain that obtains configuration
           parameters such as a (e.g.,  network address. address) using DHCP protocol

         o "DHCP server"

           A DHCP server is an Internet host that returns provides
           configuration parameters to DHCP clients.

         o "MDHCP client"

           A MDHCP client is a DHCP client that supports MDHCP
           extensions.

         o "MDHCP server"                                MDHCP                    09/16/97

           A MDHCP server is a DHCP server that supports MDHCP
           extensions.

      o "BOOTP relay agent"

        A BOOTP relay agent or relay agent is an Internet host or
        router that passes DHCP messages between DHCP clients and DHCP
        servers. DHCP is designed to use the same relay agent behavior
        as specified in the BOOTP protocol specification.

      o "binding"

        A binding is a collection of configuration parameters,
        including at least an IP address, associated with or "bound to"
        a DHCP client.  Bindings are managed by DHCP servers.

  1.3. Motivation and protocol requirements.

  For multicast applications to be ubiquitous, there is a need to
  standardize on a protocol to allocate multicast addresses to the
   applications. an
  application. Following are the set of requirements on such a
  protocol.

  Conflict Free Allocation: When two applications obtain a multicast
  address (using a common multicast address allocation protocol), both
  applications are may be allocated identical addresses only if it can be
  guaranteed that no hosts will receive multicasts using same address
  from both the applications on the same network interface provided
  that the multicast scoping is implemented correctly.

   Session protocol independence: The address allocation protocol

   should be independent of existing

    Patel and future session control
   protocol. For example, it must be suitable for applications that
   use SAP (session announcement protocol) and SIP (session invitation
   protocol).

   Small response time: Shah                                               3
                                MDHCP                    11/20/97

   Quick response: The application should not have to wait for a long
   time before it can be sure that able to determine if it can use a multicast address.
   The response time should primarily be a function of network and
   system delays only and should not be in the order of several
   minutes.

   Low network load: The multicast address allocation protocol is a
   control protocol. It Therefore, it should be designed to impose minimal load on the
   network. In particular, it should not require periodic
   broadcast/multicast messages from every application. Specifically,                                MDHCP                    09/16/97 the address allocation protocol should not
   overload a modem line when used by a dial-in user.

   Work with power managed systems: The protocol should not require
   the client systems to be on all the time. It is perfectly
   acceptable that once the multicast address is allocated, the system System may suspend or turn be in on, off for some time. The system may come back to
   full or low
   power just before state between the application starts multicasting
   traffic. address allocation and usage period.

   Multicast address scopes: The protocol must be able to allocate both
   the administratively scoped addresses and global addresses.

   Efficient use of address space: The multicast address space is
   smaller then IP address space. Moreover, a host or application may
   require multiple address. addresses. Therefore, efficient use of address
   space is a design goad goal of multicast address allocation protocol.

  1.4. MHDCP Protocol Summary

   From the client's point of view, protocol standpoint, MDHCP is an extension of the DHCP. As
   in normal DHCP
   mechanisms. protocol, a MDHCP client requests multicast
   address(es) from the MDHCP server for a specified multicast scope.
   The MDHCP servers assigns multicast addresses address(es) to the hosts to be
   used within a specific the requested scope, and valid for a specific

   period. A client may request multiple multicast addresses.

   The client requests a multicast address(es) to be used for a
   specific multicast scope available to it, and for over a specific lease period.
   The MDHCP server would ideally assign the address from the
   requested scope or may allocate it for a different scope. However,
   if it allocates the address from a different scope, it will provide

   this information as an option. The DHCP server MUST provide a TTL
   value. value of the address. The multicast packets client,
   when using the assigned address MUST NOT should not use a the TTL value larger then
   than the one provided.  The lease period is defined by the duration
   of the lease and the time at which the lease becomes effective. Since the client may want to extend lease
   at a later time, the DHCP server SHOULD make every attempt at
   allocating an address which is not currently allocated to any other
   client. The
   DHCP server MUST NOT allocate the same addresses address to different clients
   with overlapping lease period. period and scope. The protocol also allows
   client to request more than one address at a time.

   Before requesting a multicast
   scope address, a client needs to obtain the
   list of multicast scopes available on the MDHCP server. The
   multicast scope-list is one of the DHCP MDHCP configuration parameters.
   The scope list may be obtained through the DHCP option described in
   [3], or may be obtained with by some other means. Similarly, the MDHCP
   server address (unicast or multicast) (multicast) may also be obtained by the option
   described in [3] or by some other means. can be configured on the client.

   The MDHCP server is not required to be co-located with a DHCP
   server. Therefore, in a typical deployment, there may be fewer MDHCP                    09/16/97
   servers then the DHCP servers.

   The MDHCP protocol uses M flag and a set of options defined below.

    Patel and Shah                                               4
                                MDHCP                    11/20/97

   2.  MDHCP messages and options.

   The following options and flags are used by MDHCP extensions.

  2.1. M flag

   A new flag (M) is defined to differentiate the MDHCP messages from
   DHCP messages.  All the messages (DHCPDISCOVER, DHCPOFFER etc.) use
   M flag (this is a new flag) defined below to indicate multicast address negotiations. The
   second bit of the flag field (bit 1) defines M (multicast) flag.
   The M bit must be set for all the message exchanges pertinent to the
   multicast address assignment. The client MUST obtain an IP address
   prior to requesting a multicast address. Therefore, B flag MUST not
   be set when M flag is set.

                                     1 1 1 1 1 1

                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5

                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                |B|M|           MBZ             |

                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                B:  BROADCAST flag

                M:  Multicast address request flag.

                MBZ:  MUST BE ZERO (reserved for future use)

  2.2. Multicast Scope Option

   This option is used by the client to indicate the multicast scope
   for the requested multicast address. address(es). It is also used to indicate
   the scope of the assigned address by the DHCP server. If this option
   is not specified, the DHCP server MAY allocate an address from a
   DEFAULT scope or reject the request.                                MDHCP                    09/16/97

                                     1 1 1 1 1 1
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3

         Code  Len      Scope Id

        +-----+-----+-----+-----+-----+-----+

        | 101 | 4 5

                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                | code          | length=4   |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i1  | Scope id i2  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i3  | Scope id i4  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        +-----+-----+-----+-----+-----+-----+

   The client may obtain the scope list through the option described in
   [3] or using some other means. The scope id is the numeric
   representation of the scope as described in [3]. The 'code' for this
   option is 101. 101 and the length is 4.

    Patel and Shah                                               5
                                MDHCP                    11/20/97

  2.3. Start time Option

   The start time is used in a client request (DHCPDISCOVER or
   DHCPREQUEST) to allow the client to request the starting time for
   the use of the assigned address. This option allows client to
   request a multicast address for use at a future time.

                                     1 1 1 1 1 1
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5

                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                | code

         Code  Len      Time

        +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

        | length=4 102 |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8   | t1  | t2  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                | t3  | t4  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                | t5  | t6  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                | t7  | t8  |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

   The time value is the decimal representation of Network Time
   Protocol (NTP) time values in seconds [5].

   The 'code' for this option is 102. 102 and the length is 8.

   If IP Address Lease Time option specifies [2] the duration of the
   lease beginning at Start Time option value.                                MDHCP                    09/16/97

  2.4. Multicast TTL Option

   This option specifies the TTL value to be used with the multicast
   address. The TTL is specified as an octet with a value between 1
   and 255. The implied value of this option is 255 when not included.

         Code  Len    Multicast TTL

        +-----+-----+-----+

        | 103 | 1 1 1 1 1 1
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | code n   |

        +-----+-----+-----+

   The 'code' for this option is 103 and the length is 1.

  2.5. Number of Addresses Requested Option

   This option specifies the number of addresses requested by the
   client. The client MAY obtain more than one address either by
   repeating the protocol for every address or by requesting all the
   addresses at the same time via this option. The server MAY use this
   option to indicate to the client the number of addresses it has
   allocated to the client. When the client is requesting only one
   address, this option need not be included.

         Code  Len    Number of Addresses

        +-----+-----+-----+-----+

        | length=1 104 |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2   | TTL n         |
                +-+-+-+-+-+-+-+-+

        +-----+-----+-----+-----+

   The 'code' for this option is 103.

  2.5. 104 and the length is 2.

    Patel and Shah                                               6
                                MDHCP                    11/20/97

  2.6. Client Port Option

  In order to facilitate implementations outside the operating system
  kernel, and to allow two separate client implementations: one for
  DHCP and one for MDHCP, if this option is specified, the MDHCP server
  MUST use the source port number used in the DHCPDISCOVER,
  DHCPREQUEST, DHCPINFORM, and DHCPRESEASE as the destination port
  number in the response messages.

                 0

         Code  Len    Port

        +-----+-----+-----+

        | 105 | 1 2 3 4 5 6 7
                +-+-+-+-+-+-+-+-+   | code n   |
                +-+-+-+-+-+-+-+-+

        +-----+-----+-----+

   The 'code' for this option is 105.

   3.   MDHP protocol

   The client needs to obtain 105 and the IP address length is 1.

  2.7. List of Address Ranges Allocated

  This option is used by the MDHCP server (this
   may be a unicast or a multicast address for MDHCP group), and to provide the
   multicast scope list. This list may be obtained as part of all the
   normal DHCP protocol using
  address ranges allocated to the options specified in client when client requests more than
  one addresses. When a client requests only one address, the server
  uses the ‘yiaddr’ field specify the allocated address. When a client
  requests more than one address, additional address ranges are listed
  via this option.

         Code  Len     Address Range List

        +-----+-----+-----+-----+-...-+-----+

        | 105 | n   | L1  | L2  |     | Ln  |

        +-----+-----+-----+-----+-----+-----+

   Where the Address Range List is of the follwing format.

        StartAddress1  BlockSize1 StartAddress2 BlockSize2 ...

        +---+---+---+---+---+---+---+---+---+---+---+---+--...--+

        |S11|S12|S13|S14|B11|B12|S21|S22|S23|S24|B21|B22|       |

        +---+---+---+---+---+---+---+---+---+---+---+---+-------+

   The 'code' for this option is TBD and the minimum length is 6.

  3. MDHP protocol

   The client first needs to know the group multicast address of the
   MDHCP servers, and the multicast scope list. This address and the
   scope list may be obtained by requesting the options specified in
   [3] from DHCP servers via DHCPINFORM or by some from other means.

   The repository of
   network configurations.

   At this point, client selects one has two ways of obtaining the multicast scopes
   address(es) from the server.

    Patel and requests multicast Shah                                               7
                                MDHCP                    11/20/97

   In the first method [see Figure 1], the client is requesting
   address(es) from any of the MDHCP servers. servers configured to hand out
   addresses from a given scope. The fields client selects a scope and options that

   are different from sends
   out a DHCPDISCOVER
   message to the normal DHCP multicast address of the MDHCP servers. The server
   responds by sending DHCPOFFER message exchange are summarized
   in Table 1 directly to 3.  details on rest the client. The
   client then sends DHCPREQUEST messages to the multicast address.
   of the parameters, please MDHCP                    09/16/97

   consult servers. The selected server responds by sending
   DHCPACK message directly to the client as in normal DHCP RFC [1]. protocol.
   The multicast addresses DHCPDICOVER and DHCPREQUEST messages are renewed or
   released using received by
   only the multicast capable DHCP exchanges for network addresses as defined
   in servers, and therefore, there is no
   conflict between the MDHCP and DHCP RFC [1].

   Note that all messages. Further, the messages in this
   for renewing and releasing lease are sent directly to the MDHCP
   servers only, and therefore, there is conflict between DHCP and
   MDHCP message interpretation by a non-MDHCP capable server. The
   fields and options that are different from the normal DHCP message
   exchange are summarized in Table 1 to 3.  For details on rest of the
   fields, please refer DHCP RFC [1].

   The client can later renew or release the multicast address by using
   DHCPREQUEST and DHCPRELEASE message exchanges as defined in the DHCP
   RFC [1].

   At any time, if the MDHCP server is unable to satisfy the
   DHCPREQUEST message (e.g., the requested address has been
   allocated), the server MUST respond with a DHCPNAK message.

   Note that all the messages in this exchange have their M flag set
   and B flag not set.

   In the second method [see Figure 2] the client is requesting
   address(es) directly from a specific MDHCP server. When a client
   knows the IP address of the MDHCP server from which it can obtain a
   multicast address(es) from a give scope, it MAY skip the discover
   phase ( i.e. DHCPDISCOVER and DHCPOFFER message exchange ) and
   directly start with unicasting DHCPREQUEST message to the server. If
   this fails, the client SHOULD revert back to the first method.

   The MDHCP client may need to be deployed on the client machines
   where DHCP client implementation is not capable of filtering out the
   MDHCP messages. In that case, the MDHCP client MUST use a port
   number different from ‘DHCP client port(68)’. The MDHCP client MUST
   specify this port in the DHCPDISCOVER and DHCPREQUEST messages via
   ‘Client Port Option’.

   The MDHCP Client MUST provide client identifier option when sending
   messages for multicast address assignment. The client generates a
   unique key and uses that as a client identifier in the DHCPDISCOVER
   message. The client identifier is the key to distinguish the client
   request and to avoid duplicate address allocation.

   Each client may be running several different multicast enabled
   applications, and each application may require separate multicast
   address(es). Client MUST use separate unique client identifier when

    Patel and Shah                                               8
                                MDHCP                    11/20/97

   requesting separate multicast address(es) for each application. request. A client
   implementation may choose to use hardware address, hardware

   type and application
   instance number and time of request to generate unique client
   identifier.                                MDHCP                    09/16/97

  Field      DHCPOFFER identifiers.

   The following tables [Table 1, Table 2] describes the fields and
   options that are relavent to MDHCP protocol but are different from
   the normal DHCP protocol [1]

   Field      DHCPOFFER            DHCPACK             DHCPNAK

   -----      ---------            -------             -------

  'flags'    Set 'M' Bit.         set 'M' Bit         set 'M' bit

             BROADCAST bit 0      BROADCAST bit 0     BROADCAST bit 0

  'ciaddr'   'ciaddr' from        'ciaddr' from       0

             DHCPDISCOVER or 0    DHCPREQUEST or 0

  'yiaddr'   Starting   Multicast address of  Starting    Multicast address of 0
             the multicast block  the multicast block

             assigned to client   assigned to client

  'siaddr'   Server's IP address  Server's IP address 0

             reachable from the   reachable from the

             client.              client.

  'chaddr'   'chaddr' from        'chaddr' from       'chaddr' from

             client DHCPDISCOVER  client DHCPREQUEST  client DHCPREQUEST

             message              message             message

  'file'     may contain options  may contain options    (unused)

  'options'  options              options

   Option                    DHCPOFFER    DHCPACK            DHCPNAK

   ------                    ---------    -------            -------

   IP address lease time     MUST         MUST (DHCPREQUEST)               MUST NOT
  Server identifier

   Lease Start Time          MUST         MUST               MUST
  Multicast TTL NOT

   Server identifier         MUST         MUST               MUST NOT

   Multicast Block size      MAY          MAY Scope           MUST NOT
  Cookie         MUST         MAY               MUST NOT

              Table 1:  Fields and options that are different in
                           multicast DHCP server messages.

    Patel and Shah                                               9
                                MDHCP                    09/16/97                    11/20/97

     Field      DHCPDISCOVER      DHCPREQUEST           DHCPDECLINE,           DHCPRELEASE

     -----      ------------      -----------           -----------

     'flags'    Set 'M' Bit.      set 'M' Bit           set 'M' bit

                BROADCAST bit 0   BROADCAST bit 0       BROADCAST bit 0

     'ciaddr'   0 or client's network     0 or client's network         0

                network addr reachable      network addr reachable
                from the server   from the server

     'chaddr'   may contain       may contain           may contain

                hardware address  hardware address     hardware address   ignored           ignored               ignored

     'options'  options           options               (unused)

     Option                  DHCPDISCOVER   DHCPREQUEST  DHCPDECLINE,    DHCPRELEASE

     ------                  ------------   -----------    -----------
     Requested IP address       MAY           MUST (in      MUST

                                              SELECTING or (DHCPDECLINE),
                                              INIT-REBOOT)  MUST NOT
                                              MUST NOT (in  (DHCPRELEASE)
                                              BOUND or
                                              RENEWING)

     Start time                 MAY           MAY           MUST NOT
     Client identifier          MUST          MUST          MAY

             Table 2:  Fields and options that are different in
                               multicast DHCP client messages

   --------------------------------------------------------------------
   |              |INIT-REBOOT  |SELECTING         |RENEWING|REBINDING |

   --------------------------------------------------------------------
   |multi/unicast |multicast    |multicast if      |unicast |multicast |
   |              |             |multicast DISCOVER|        |          |
   |              |             |unicast otherwise |        |          |
   |server-ip     |MUST NOT     |MUST              |MUST NOT|MUST NOT  |
   |requested-ip  |MUST         |MUST              |MUST NOT|MUST NOT  |
   |ciaddr        |IP addr      |IP addr           |IP addr |IP address|
   ---------------------------------------------------------------------

              Table 3: Client messages from different states                                MDHCP                    09/16/97

  3.1.  DHCPDISCOVER Message.

   If the unicast address of a MDHCP server is known and it supports
   the desired multicast scope, the MDHCP client SHOULD send a
   DHCPDISCOVER address to the MDHCP server. If the MDHCP server fails
   to allocate address(es) or fails to respond, the DHCP client SHOULD
   send a multicast DHCPDISCOVER message to the group address
   (multicast) of the MDHCP server. In both cases, if the client uses
   non-standard DHCP port number, it MUST specify the client port

   option. The client MUST also specify its IP address in the ciaddr
   field so that the MDHCP server and respond to the client request
   with a unicast message. The B flag must not be set and M flag MUST
   be set.

   The client MUST include client identifier option.
   In addition, the DHCPDISCOVER option SHOULD include the following

   options:

   o DHCP Scope,
   o Start time,
   o Lease time (duration)

   If any of these options are not specified, the DHCP server
   may assume default values.

  3.2.  DHCPOFFER Message.

   The DHCP server may respond to a DHCPDISCOVER message with a
   unicast DHCPOFFER the client. This message MUST includes an
   available multicast address using ``yiaddr'' field. The

   MDHCP server SHOULD reserve the offered address. When allocating
   the address, the server MUST make every effort to ensure that the
   address is not in use for the lease period.

   The server MUST include configuration parameters such as DHCP
   scope, start and lease time, in the DHCPOFFER message, if different
   from the ones requested. The MDHCP server must specify a cookie

   value in this message and this cookie MUST be specified in all the
   subsequent messages exchanged between the MDHCP clients and server
   pertaining to associated address(es). The MDHCP server MUST use the
   cookie to identify the addresses instead of the client IP address.

  3.3.  DHCPREQUEST

   The client will select a multicast address(es) from a DHCPOFFER                                MDHCP                    09/16/97

   response. The client SHOULD send a unicast DHCPREQUEST message
   indicating the selected multicast address(es) to the MDHCP server,
   when the DHCPOFFER was in response to a unicast DHCPDISCOVER

   message, and using a multicast message, when the DHCPOFFER was in
   response to a multicast address. It MUST include multicast address
   option field in the response. If the number of address selected are
   different from the number of offered address, the client MUST also
   include the multicast block size option.

   The M flag MUST be set and B flag MUST NOT be set.

  3.4.  DHCPACK.

   If the multicast address(es) are still available, the MDHCP server
   MUST reserve the address and send a DHCPACK message. Any
   configuration parameters in the DHCPACK message SHOULD NOT conflict

   with the ones in earlier DHCPOFFER message. The M flag MUST be set
   and B flag MUST NOT be set.

  3.5.  DHCPNACK

   The server MAY choose to mark the multicast address in DHCPOFFER

   unavailable to the client. In that case it will send DHCPNACK
   message. The M flag MUST be set and B flag MUST NOT be set.

  3.6.  Renewing and termination of lease

   The client may choose to release address(es) before the lease time

   has expired. The usual DHCP messages are used for this purpose.

   The M flag MUST be set and B flag MUST not be set. Moreover, the
   client port option SHOULD be specified, if the client is using a
   port different from the standard DHCP port. The cookie MUST be
   specified with RENEW and RELEASE messages.

   4.   Examples of usage

   The MDHCP server is not required to be co-located with a DHCP
   server. Therefore, in a typical deployment, there may be fewer
   MDHCP servers then the DHCP servers. We consider specific examples
   of DHCP configurations and the use of MDHCP protocol extensions.

   4.1.         One MDHCP server                                MDHCP                    09/16/97

   There is one MDHCP server which is configured to allocate multicast
   addresses to a client and there may be many DHCP servers. The DHCP
   servers should be configured to provide the address of the MDHCP

   server capable of allocating multicast address to the MDHCP client,
   and should include a multicast scope list supported by the MDHCP
   server. The client may obtain the DHCP server address and scope
   list through DHCP client configuration procedure (and may use
   DHCPINFORM message). The client then selects a multicast scope from
   which the multicast address is to be requested and sends out a
   unicast DHCPDISCOVER address and includes multicast scope, start
   time, and lease time information using DHCP options. It

   may also specify multicast block size. The MDHCP server
   responds with an DHCPOFFER for multicast address and includes a TTL
   value to be used with this address. The client sends out a
   DHCPREQUEST message and includes the selected. If the address is
   still available, the server responds with an DHCPACK message, else
   responds with a NACK message.

   Since the DHCP messages are directly send to the MDHCP server, the
   server is capable of interpreting M flag and therefore, there will
   be no conflict between the interpretation of DHCP and MDHCP
   messages.                                MDHCP                    09/16/97

                                Client          Server (selected)
                                  v               v

                                  |               |
                        Obtain IP address         |
                                  |               |
                                  |               |
                   Begin multicast address request|
                                  |               |
                                  |               |
                                  |\_____________ |

                                  | DHCPDISCOVER \|
                                  |               |
                                  |          Determines
                                  |          address(es)
                                  |               |
                                  |  ____________/|
                                  | /DHCPOFFER    |

                                  |/              |
                                  |               |
                                 \|               |
                        Selects Address(es)       |
                                  |               |
                                  |\_____________ |
                                  |  DHCPREQUEST \|
                                  |               |

                                  |     Commits address(es)
                                  |               |
                                  | _____________/|
                                  |/ DHCPACK      |
                                  |               |
                    assignment complete           |
                                  |               |

                                  .               .
                                  .               .
                                  |               |
                         Graceful release         |
                                  |               |
                                  |\_____________ |
                                  |  DHCPRELEASE \|
                                  |               |

                                  |        Discards lease
                                  |               |
                                  v               v
     Figure 1: Timeline diagram of messages exchanged between MDHCP
     client and servers when allocating multicast address(es) using
     unicast messages to a MDHCP capable server.                                MDHCP                    09/16/97

  4.2.  One or more MDHCP servers

   If one or more MDHCP servers are available to a MDHCP client for
   the purpose of assigning multicast addresses, the DHCP scope list
   option SHOULD specify an administratively scoped group address used
   by the MDHCP servers to receive DHCPDISCOVER messages. Each scope

   in the scope list MUST be supported by at least one server listening
   to the group multicast address used by MDHCP servers.

   The client SHOULD select a scope and send out a DHCPDISCOVER,
   DHCPREQUEST messages to the group multicast address. The multicast
   DHCPREQUEST message is only received by the MDHCP capable DHCP
   servers, and therefore, there is no conflict between the MDHCP and

   DHCP messages. Further, the messages for renewing and releasing
   lease are sent directly to the MDHCP servers only, and therefore,
   there is conflict between DHCP and MDHCP message interpretation by time              MAY            MAY            MUST NOT

     Client identifier       MUST           MUST           MAY

     Multicast Scope         SHOULD         SHOULD         MAY

     Client Port             MUST(if using  MUST (if using MUST NOT

                             a non-MDHCP capable server.

   A summary of fields of MDHCP in messages different    a different

                             port)          port)

                Table 2:  Fields and options that are different from
   the corresponding DHCP [1] messages are specified in Tables 1 to 3.

   In some cases, the client may be aware of the unicast address of an
   MDHCP capable server, and may also be aware of the group
                                  multicast
   address of the MDHCP capable servers. In that case, the DHCP client
   SHOULD first try to use the unicast address, messages

    Patel and if unsuccessful,
   SHOULD try the group multicast address for MDHCP servers. Shah                                              10
                                MDHCP                    09/16/97                    11/20/97

                Server          Client          Server

            (not selected)                    (selected)

                  v               v               v

                  |               |               |

                  |     Obtain IP address         |

                  |               |               |

                  |Begin multicast address request|

                  |               |               |

                  | _____________/|\_____________ |

                  |/ DHCPDISCOVER | DHCPDISCOVER \|

                  |               |               |

              Determines          |          Determines

              address(es)         |          address(es)

                  |               |               |

                  |\              |  ____________/|

                  | \_________    | /DHCPOFFER    |

                  |  DHCPOFFER\   |/              |

                  |            \  |               |

                  |       Collects replies        |

                  |              \|               |

                  |     Selects Address(es)       |

                  |               |               |

                  | _____________/|\_____________ |

                  |/ DHCPREQUEST  |  DHCPREQUEST \|

                  |               |               |

                  |               |     Commits address(es)

                  |               |               |

                  |               | _____________/|

                  |               |/ DHCPACK      |

                  |               |               |

                  | assignment complete           |

                  |               |               |

                  .               .               .

                  |               |               |

                  |      Graceful release         |

                  |               |               |

                  |               |\_____________ |

                  |               |  DHCPRELEASE \|

                  |               |               |

                  |               |        Discards lease

                  |               |               |

                  v               v               v

        Figure 2: 1: Timeline diagram of messages exchanged between MDHCP
        client and servers when allocating multicast
               address(es) using group multicast address for MDHCP
        capable servers.

    Patel and Shah                                              11
                                MDHCP                    09/16/97

   5.                    11/20/97

               Client          Server

                  v               v

                  |               |

                  |\_____________ |

                  |  DHCPREQUEST \|

                  |               |

                  |     Commits address(es)

                  |               |

                  | _____________/|

                  |/ DHCPACK      |

                  |               |

                  | assignment complete

                  |               |

                  .               .

                  |               |

         Graceful release         |

                  |               |

                  |\_____________ |

                  |  DHCPRELEASE \|

                  |               |

                  |        Discards lease

                  |               |

                  v               v               v

        Figure 2: Timeline diagram of messages exchanged between MDHCP
                  client and servers when MDHCP server has already been
                  selected

   4.  MDHCP Protocol properties

   Conflict free address allocation: In the intranet case, each MDHCP
   server is MAY be allocated part of the administratively scoped address
   space. As long as the address space managed by MDHCP servers is
   non-overlapping for a given administrative scope, the protocol
   will allocate conflict free addresses. MDHCP protocol does not
   directly address the mechanisms for determining address allocation
   outside Intranet. However, we propose to use MDHCP as a front end
   to any future address allocation protocol for the Internet. The MDHCP DHCP
   protocol will preserve conflict free address allocation property of
   the internet multicast address allocation protocol.

   Session protocol independence: The MDHCP protocol does not dictate
   use of the address allocated, and does not rely on any session

   control protocol. Therefore, it will work with SIP or SAP based
   session control protocol.

   Small response time: The response time for MDHCP protocol is
   strictly based on the network propagation delay and the load on the
   MDHCP server.

   The MDHCP protocol does not require a client system to be on all the
   time. Thus, it poses no additional requirements on power managed
   systems.

    Patel and Shah                                              12
                                MDHCP                    11/20/97

   Multicast address scopes: The administratively scoped multicast
   address may be directly allocated by MDHCP server. However, it is
   envisioned that the MDHCP protocol will be indirectly used for
   Internet wide Multicast addresses allocation. In such deployment,
   the MDHCP server will act as a front-end to future Internet
   multicast address allocation protocols.

   Efficient use of address space: The multicast address space may be
   statically partitioned between MDHCP servers to provide sufficient
   reliability and load management on servers. However, the multicast
   based address request will be able to obtain addresses from any of
   the available servers. Alternately, the MDHCP server can be
   organized hierarchically where a master server allocates blocks of
   addresses to the child servers (using MDHCP protocol). It is also
   possible to provide further fault-tolerance using DHCP server-server
   protocol.                                MDHCP                    09/16/97

   6.

   5.  Security Considerations

   This document does not explicitly address security considerations to
   avoid redundant effort with the work in progress in DHC working
   group of IETF on securing DHCP.

   7.

   6.  Acknowledgements

   The authors would like to thank Rajeev Byrisetty, Steve Deering,
   Peter Ford, Mark Handley, Van Jacobson, David Oran, Thomas Pfenning,
   Dave Thayler, Ramesh Vyaghrapuri and the participants of IETF for
   their assistance with this protocol.

   8.

   7.  References

   [1] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,

   October 1993.

   [2] Alexander, S., and R. Droms, "DHCP Options and BOOTP Vendor

   Extensions", RFC 1533, Lachman Technology, Inc., Bucknell

   University, October 1993.

   [3] Patel, B., and Shah, M., ``Multicast address allocation

   extensions options'' <draft-ietf-dhc-multopt-00.txt>

   [4] Meyer, D., ``Administratively scoped IP Multicast'', Internet

   draft, <draft-ietf-mboned-admin-ip-space-01.txt>

   [5] D. Mills, ``Network Time Protocol version 2 specification and

   implementation'',

   9.

   8.  Author's Address

      Baiju V. Patel
      Intel Corp.
      2111 NE 25th Ave.
      Hillsboro, OR 97124

    Patel and Shah                                              13
                                MDHCP                    11/20/97

      Phone: 503 264 2422
      EMail: baiju@mailbox.jf.intel.com

      Munil Shah
      Microsoft Corporation
      One Microsoft Way
      Redmond, WA 98052

   Phone:206

      Phone:425 703 3924
      Email:munils@microsoft.com

      This document will expire on Sept, 1997                                MDHCP                    09/16/97 April, 1998

    Patel and Shah                                              14