Network Working Group                                       K. Chowdhury
Internet-Draft                                          Starent Networks
Expires: December 31, 2005 February 2, 2006                                      P. Yegani
                                                           Cisco Systems
                                                               L. Madour
                                                           June 29,
                                                          August 1, 2005

        DHCP Options for Broadcast and Multicast Control Servers

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   This document defines new options to discover the Broadcast and
   Multicast Service (BCMCS) controller in an IP network.  BCMCS is
   being developed for 3rd generation (3G) cellular telephone networks.
   Users of the service interact with a controller in the network via
   the Mobile Node (MN) to derive information required to receive
   broadcast and multicast service.  Dynamic Host Configuration Protocol
   can be used to configure the MN to acccess a particular controller.
   This document defines the related options and option codes.

Table of Contents

   1.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Overview of the 3GPP2 BCMCS Network  . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Broadcast & Multicast Service Controller Options . . . . . . .  6
     4.1   Broadcast & Multicast Service Controller Domain Name
           list for DHCPv4  . . . . . . . . . . . . . . . . . . . . .  6
     4.2   Broadcast & Multicast Service Controller Domain Name
           List Option for DHCPv6 . . . . . . . . . . . . . . . . . .  7
     4.3   Broadcast & Multicast Service Controller IPv4 address
           option for DHCPv4  . . . . . . . . . . . . . . . . . . . .  7
     4.4   Broadcast & Multicast Service Controller IPv6 Address
           Option for DHCPv6  . . . . . . . . . . . . . . . . . . . .  8
     4.5   Consideration for Client Operation . . . . . . . . . . . .  8
     4.6   Consideration for Server Operation . . . . . . . . . . . .  9  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 12
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
       Intellectual Property and Copyright Statements . . . . . . . . 14

1.  Motivation

   Dynamic Host Configuration Protocol [RFC2131] and [RFC3315] can be
   used to configure various non-IP address type of parameters.  These
   parameters are required for normal operation of various services that
   are offered over an IP network.

   Broadcast and multicast service (BCMCS) is one such service that is
   being standardized in various mobile wireless standard bodies such as
   3GPP2, OMA, and 3GPP.  A description of the BCMCS as defined in 3GPP2
   can be found in [BCMCS].

   While DHCP already defines many options for device configuration, no
   option exists for configuring a mobile device to use BCMCS.  This
   memo defines extensions for both DHCPv4 and DHCPv6 so that DHCP can
   be used to provide necessary configuration information to a mobile
   device about the BCMCS controllers.

   DHCP is being used in 3GPP2, to assist mobile nodes (MN) with the
   discovery of the BCMCS Controller in a mobile operator's IP network.
   The BCMCS includes a controller component that is responsible for
   managing the service via interaction with the MN and other network
   entities.  In this document we will call this a BCMCS controller.

   An overview of the 3GPP2 BCMCS architecture is given in the next
   section.  It provides enough information to understand the basics of
   the 3GPP2 BCMCS operation.  Readers are encouraged to find a more
   detailed description in [BCMCS].

   As described in [BCMCS], the MNs are required to know the IPv4 or the
   IPv6 address of the BCMCS controller entity so that they can download
   all the necessary information about a desired broadcast and/or a
   multicast program.  In a roaming environment static configuration of
   the BCMCS controller's IP address becomes unrealistic.  Therefore,
   DHCP is considered to be a method to dynamically configure the MNs
   with the IP address or the fully qualified domain name of the BCMCS
   controller in the 3G cellular telephone networks.

   In order to allow the MNs to discover the BCMCS controllers, the MNs
   request the appropriate option codes from the DHCP server using
   Parameter Request List option.  The DHCP servers need to return the
   corresponding configuration options that carry either BCMCS
   controller's IP address or fully qualified domain name based on
   configuration.  This document defines the necessary options and
   option codes.

2.  Overview of the 3GPP2 BCMCS Network

   The Broadcast and Multicast Service architecture in a 3G cellular
   telephone network such as 3GPP2 has the following model:

                              +------------+   +--------+
                              |   BCMCS    |   |        |
                              | Controller |   |  DHCP  |
                              |            |   | Server |
                              +------------+   +--------+
   +----+        +------------+    +------------+
   |    |        |            |    |            |
   | MN/| bearer |   Radio    |    | BCMCS      |
   |User|<-------|   Access   |<---| Content    |
   |    |        |   Network  |    | Server     |
   +----+        +------------+    +------------+

   Note that this figure is shown here for a basic understanding of how
   Broadcast and Multicast service works in a 3G cellular telehone
   network.  The network elements except MN/user and the DHCP server are
   not relevant to the text in this document.

   The MN interacts with the BCMCS Controller to request broadcast/
   multicast program information from the network (e.g., scheduled time,
   multicast IP address, port numbers).  The MN may also be
   authenticated by the BCMCS Controller while downloading the relevant
   program security related information (such as encryption key).  These
   interactions may happen via HTTP and XML as defined in [BCMCS].
   There may be more than one BCMCS controller in the network.  The MN
   should discover the appropriate BCMCS controller to request the
   relevant program information.  For details of Broadcast and Multicast
   Service operation in 3GPP2, see [BCMCS].

3.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC 2119.

4.  Broadcast & Multicast Service Controller Options

   This section defines the configuration option for the BCMCS
   controller of the broadcast and multicast service.

4.1  Broadcast & Multicast Service Controller Domain Name list for

   The general format of the BCMCS Controller Domain list option for
   DHCPv4 is as follows:

           Code  Len  FQDN(s) of BCMCS Controller
         | TBD1|  n  |  s1 |  s2 |  s3 |  s4 | s5  |  ...

   The option MAY contain multiple domain names, but these domain names
   SHOULD be used to construct SRV lookups as specified in [BCMCS],
   rather than querying for different A records.  The client MUST can try any
   or ALL of the records in the order listed, applying the mechanism described in
   [BCMCS] for each entry.  The client only resolves the subsequent domain names if attempts to contact the first one failed or yielded
   no common transport protocols between the client and construct the BCMCS
   controller or denote a domain that is administratively prohibited by
   client's policy. SRV lookups.  The use list of multiple
   domain names is not meant to replace the SRV
   records, but rather to allow a single DHCPv4 server to indicate MAY conatin the
   BCMCS controllers in domain name of the wireless access provider's network. provider and
   it's partner networks that also offer broadcast and multicast

   If the length of the domain list exceeds the maximum permissible
   length within a single option (254 octets), then the domain list MUST
   be represented in the DHCPv4 message as specified in [RFC3396] .  An
   example case when two controller domain names, and are returned will be:

   |TBD1| 26 | 7  | 'e'| 'x'| 'a'| 'm'| 'p'| 'l'| 'e'|  3 |
   |'c' | 'o'| |'o'| 'm'|  0 |  7  | 'e'| 'x'| 'a'| 'm'| 'p'| 'l'| 'e'|
   |'e' |  3 | 'n'| 'e'| 't'|  0 |  7 |

4.2  Broadcast & Multicast Service Controller Domain Name List Option
     for DHCPv6

   The semantics and content of the DHCPv6 encoding of this option is
   exactly the same as the encoding described in the previous section,
   other than necessary differences between the way options are encoded
   in DHCPv4 and DHCPv6.

   Specifically, the DHCPv6 option for the BCMCS Control Server Domain
   Names has the following format:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |      OPTION_BCMCS_SERVER_D    |         option-length         |
     |          BCMCS Control Server Domain Name List                |
     |                              ...                              |

   option-code: OPTION_BCMCS_SERVER_D (TBD2).

   option-length: Length of the 'BCMCS Control Server Domain Name List'
   field in octets; variable.

   BCMCS Control Server Domain Name List: Identical content as in
   Section 4.1 (except the Code and Len fields).

4.3  Broadcast & Multicast Service Controller IPv4 address option for

   The Length byte (Len) is followed by a list of IPv4 addresses
   indicating BCMCS controller IPv4 addresses.  The BCMCS controllers
   MUST be listed in order of preference.  Its minimum length is 4, and
   the length MUST be a multiple of 4.  The DHCPv4 option for this
   encoding has the following format:

          Code   Len  Address 1               Address 2
         |TBD3 |  n  | a1  | a2  | a3  | a4  | a1  |  ...

4.4  Broadcast & Multicast Service Controller IPv6 Address Option for

   This DHCPv6 option MUST carry one or more 128-bit IPv6 address(es) of
   the BCMCS Controller in a operator's network.

      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_BCMCS_SERVER_A    |         option-length         |
     |                                                               |
     |    BCMCS Control server-1 address (IPv6 address)              |
     |                                                               |
     |                                                               |
     |                                                               |
     |    BCMCS Control server-2 address (IPv6 address)              |
     |                                                               |
     |                                                               |
     |                              ...                              |

   option-code: OPTION_BCMCS_SERVER_A (TBD4).

   option-length: Length of the 'BCMCS Control Server IPv6 address'
   field in octets; variable.

4.5  Consideration for Client Operation

   For DHCPv6, a client MAY request either or both of the BCMCS
   Controller Domain Name List and the IPv6 Address options in the
   Options Request Option (ORO) as described in [RFC3315].

   If a client receives both the BCMCS Controller Domain Name List and
   IPv6 Address options, it SHOULD use the Domain Name List option.  In
   this case, the client MAY SHOULD NOT use the BCMCS Controller IPv6
   Address option only if unless the servers in the BCMCS Controller Domain Name
   List can not be resolved or reached.

4.6  Consideration for Server Operation

   A server MAY send a client either the BCMCS Controller Domain Name
   List Option or the BCMCS Controller IPv6 Address/IPv4 Address options
   if the server is configured to do so.

   In case of DHCPv6, If a client requests both options and the server
   is configured with both types of information, the server MAY send the
   client only one of these options if it is configured to do so.  In
   this case the server SHOULD send the BCMCS Controller Domain Name
   List option.

   A server configured with the BCMCS Controller IPv6 Address
   information MUST send a client the BCMCS Controller IPv6 Address
   option if that client requested only the BCMCS Controller IPv6
   address option and not the BCMCS Controller Domain Name List option
   in the ORO [RFC3315].

   If a client requests for the BCMCS Controller IPv6 option and the
   Server is configured only with the Domain Names, the Server MUST
   return the Domain Names List and vice versa.

   The DNS name(s) MUST be concatenated and encoded using the technique
   described in section 3.3 of "Domain Names - Implementation And
   Specification" [RFC1035].  DNS name compression MUST NOT be used.

   The following table summarizes the server's response for DHCPv6:

      Client sends in ORO     Domain Name List        IPv6 Address List

      Neither option          SHOULD                  MAY
      Domain Name List        MUST                    MAY
      IPv6 Address            MAY                     MUST
      Both options            SHOULD                  MAY

5.  Security Considerations


   This document does not introduce any new security considerations concerns beyond
   those specified in the base basic DHCP spec [RFC2131] applies.
   An attacker may change information of the BCMCS Controller in packets
   that are in-tranist from DHCP server to the MN, if integrity
   protection is not in place. and DHCPv6 [RFC3315]
   specifications.  In that event, the user absence of message integrity protection for
   these options, an attacker could modify the Broadcast
   & Multicast service may be diverted option values to a rogue BCMCS controller.
   frustrate or divert requests for broadcast service.

6.  IANA Considerations

   The following option codes for Broadcast & Multicast Service
   Controller option must be assigned by IANA:

   1.  The BCMCS Controller Domain Name list (section 4.1) has been
   assigned a value of TBD1 from the DHCPv4 option space.

   2.	The BCMCS Controller Domain Name list (section 4.2) has been
   assigned a value of TBD2 from the DHCPv6 option space, and a name of

   3.  The BCMCS Controller IPv4 address option (section 4.3) has been
   assigned a value of TBD3 from the DHCPv4 option space.

   4.  The BCMCS Controller IPv6 address option (section 4.4) has been
   assigned a value of TBD4 from the DHCPv6 option space, and a name of

   The DHCP options should be registered in

   The DHCPv6 options should be registered in

7.  Acknowledgements

   Thanks to the following indivduals for their review and constructive
   comments during the development of this document:

   AC Mahendran, Jun Wang, Raymond Hsu, Jayshree Bharatia, Ralph Droms,
   Ted Lemon, Margaret Wasserman, and Thomas Narten. Narten, Elwyn Davies, Pekka
   Savola, and Bert Wijnen.

8.  Normative References

   [BCMCS]    3GPP2,,
              "X.S0022, Broadcast and Multicast Service in cdma2000
              Wireless IP Network. (pending publication)",
              December 2004.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3396]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
              Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
              November 2002.

Authors' Addresses

   Kuntal Chowdhury
   Starent Networks
   30 International Place
   Tewksbury, MA  01876

   Phone: +1 214-550-1416
   Parviz Yegani
   Cisco Systems
   3625 Cisco Way
   San Jose, CA  95134

   Phone: +1 408-832-5729

   Lila Madour
   8400, Decarie Blvd
   Town of Mount Royal, Quebec  H4P 2N2

   Phone: +1 514-345-7900

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