dhc Group                                                       R. Droms
Internet-Draft                                                   B. Volz
Intended status: Informational                                  O. Troan
Expires: May 31, 2007 Standards Track                     Cisco Systems, Inc.
                                                       November 27, 2006
Expires: August 10, 2009                                        O. Troan
                                                          No Affiliation
                                                        February 6, 2009

        DHCPv6 Relay Agent Assignment Notification (RAAN) Option

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   The DHCP Relay Agent Assignment Notification (RAAN) option is sent
   from a DHCP server to a DHCP relay agent to inform the relay agent of
   IPv6 addresses that have been assigned or IPv6 prefixes that have
   been delegated to DHCP clients.

1.  Introduction

   The DHCP Relay Agent Assignment Notification (RAAN) option
   encapsulates address and prefix options to indicate that an address
   or prefix has been assigned.  The option may also carry other
   information required by the network element for configuration related
   to the assigned address or prefix.

   For example, a network administrator uses the RAAN option to inform a
   relay agent of a prefix that has been delegated through DHCP PD to a
   DHCP client.  The relay agent notifies the network element on which
   it is implemented of the delegation information so the network
   element can add routing information about the delegated prefix into
   the routing infrastructure.

2.  Terminology

   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be
   interpreted as described in RFC 2119 [1]. [RFC2119].

   The term "DHCP" in this document refers to DHCP for IPv6, as defined
   in RFC 3315 [2]. [RFC3315].  The terms "DHCP prefix delegation" and "DHCP
   PD" refer DHCP for IPv6 prefix delegation, as defined in RFC 3633 [3]

   Additional terms used in the description of DHCP and DHCP prefix
   delegation are defined in RFC 3315 and RFC 3633.  In this document
   "assigning" an IPv6 prefix is equivalent to "delegating" a prefix.

3.  Option Semantics and Usage

   The RAAN option carries information about assigned IPv6 addresses and
   prefixes.  It encapsulates IA Address options (RFC 3315) and/or IA
   Prefix options (RFC 3633), and possibly other options that carry
   other information related to the assigned IPv6 address or prefix.

   The DHCP server is responsible for synchronizing any state created by
   a node through the use of the RAAN option.  For example, if a DHCP
   server receives a Release message for a delegated prefix, it causes
   the node to delete any state associated with that prefix by sending a
   RAAN option containing an IA Prefix option with the released prefix
   and a valid lifetime of zero.

   When a DHCP server sends this option to a relay agent, it MUST
   include all addresses and prefixes assigned to the client on the link
   to which the option refers at the time the option is sent.

   Examples of use:

   o  Populate an ACL with an assigned IPv6 address if the network
      security policy requires limiting IPv6 forwarding to devices that
      have obtained an address through DHCP
   o  Inject routing information into a routing infrastructure about a
      delegated prefix on behalf of a requesting router

4.  Relay Agent Behavior

   A relay agent that wants information from the server in a RAAN option
   includes an ORO requesting the RAAN option in its Relay-Forw message.
   A relay agent may do this for any relayed message, regardless of the
   message type or the message contents.

   When a relay agent receives a Relay-Reply message containing a RAAN
   option, the relay agent may forward that option data to the node in
   which the relay agent is instantiated.  If no RAAN option is included
   in the Relay-Reply, the relay agent MUST NOT assume anything with
   regard to RAAN data and MUST NOT forward any indication to the node
   in which the relay agent is instantiated.

   If a node creates state based on the information included in this
   option, it MUST remove that state when the lifetime as specified in
   the option expires.

5.  Server Behavior

   When a server is responding to a request and the ORO contains an RAAN
   option, the server SHOULD include a RAAN option with all of the
   addresses and prefixes that have been (or are being assigned) to the
   client.  If no addresses or prefixes are assigned, the server SHOULD
   send a RAAN option with no addresses or prefixes.

   If the DHCP server does include this option in a Relay-Reply message,
   it MUST include it in the option area of the Relay-Reply message sent
   to the relay agent intended as the recipient of the option.

   If the message received from the client contains no Client Identifier
   option or the server is otherwise unable to identify the client or
   the client's link (perhaps because of missing or invalid data in the
   request), the server MUST NOT include a RAAN option in the response.

6.  Option format

   The RAAN option 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-code           |            length             |
    |                      encapsulated-options                     |
    .                                                               .
    .                                                               .
    .                                                               .

   option-code          OPTION_AGENT_NOTIFY (TBD)

   length               length of encapsulated options, in octets

   encapsulated-options DHCP options to be delivered by the relay agent
                        Assignment Notification option

7.  Encapsulating DHCP options in the RAAN Option

   The contents of options encapsulated in the RAAN option are
   interpreted according to the use of those options in the node on
   which the relay agent is implemented.  For the purposes of address
   and prefix assignment, the uses of the DHCP IA Address and IA Prefix
   options are defined in this document.

   Note that the contents of these options are not necessarily the same
   as in the corresponding options sent to the DHCP client.

7.1.  IA Address option

   The fields in an IA Address option (OPTION_IAADDR, option code 5) are
   used as follows:

   IPv6 address        The IPv6 address assigned in this DHCP message

   preferred-lifetime  Not used by the relay agent; the server SHOULD
                       set this field to the preferred-lifetime of the
                       corresponding IA Address options in the message
                       to be forwarded to the client

   valid-lifetime      The lifetime of the information carried in this
                       IA Address option, expressed in units of seconds;
                       if the valid-lifetime is 0, the information is no
                       longer valid

   IAaddr-options      Not used by the relay agent; the server SHOULD
                       set this field to the IAaddr-options of the
                       corresponding IA Address option in the message to
                       be forwarded to the client

7.2.  IA Prefix option

   The fields in an IA Prefix option (OPTION_IAPREFIX, option code 28)
   are used as follows:

   preferred-lifetime  Not used by the relay agent; the server SHOULD
                       set this field to the preferred-lifetime of the
                       corresponding IA Prefix options in the message to
                       be forwarded to the client

   valid-lifetime      The lifetime of the information carried in this
                       IA Prefix option, expressed in units of seconds;
                       if the valid-lifetime is 0, the information is no
                       longer valid

   prefix-length       length for this prefix in bits

   IPv6-prefix         The IPv6 prefix assigned in this DHCP message

   IAprefix-options    Not used by the relay agent; the server SHOULD
                       set this field to the IAprefix-options of the
                       corresponding IA Prefix option in the message to
                       be forwarded to the client

8.  Requesting assignment information from the DHCP server

   If a relay agent requires the DHCP server to provide information
   about assigned addresses and prefixes, it MUST include an Option
   Request option, requesting the Assignment Notification option, as
   described in section 22.7 of RFC 3315.

9.  Reordering received DHCP messages

   The relay agent MUST use the Server Reply Sequence Number (SRSN)
   option [4] [I-D.ietf-dhc-dhcpv6-srsn-option] to detect and discard RAAN
   options contained in DHCP messages that are received out of order.

10.  IANA considerations

   IANA is requested to assign an option code from the "DHCPv6 and
   DHCPv6 options" registry
   http://www.iana.org/assignments/dhcpv6-parameters to

11.  Security considerations

   Security issues related to DHCP are described in RFC 3315 and RFC

   The RAAN option may be used to mount a denial of service attack by
   causing a node to incorrectly populate an ACL or incorrectly
   configure routing information for a delegated prefix.  This option
   may also be used to insert invalid prefixes into the routing
   infrastructure or add invalid IP addresses to ACLs in nodes.
   Communication between a server and a relay agent, and communication
   between relay agents, can be secured through the use of IPSec, as
   described in section 21.1 of RFC 3315.

12.  Changes log

   If this section is included in the document when it is submitted for
   publication, the RFC Editor is requested to remove it.

   Changes in rev -01:
   o  Added section describing use of "Server Reply Sequence Number"
      option to allow resequencing of out-of-order messages

   Changes in rev -02:
   o  Made editorial change in section 1: s/the appropriate routing
      protocols/the routing infrastructure/
   o  Updated first paragraph in Section 3 to allow multiple IA Address
      options and/or IA Prefix options
   o  Renamed section 3 to "Options Semantics and Usage"
   o  Added paragraph to section "Option Semantics and Usage" requiring
      that the DHCP server must include all addresses/prefixes for the
      client (on that link) in the RAAN option
   o  Added list of use cases to section "Option Semantics and Usage"
   o  Added section "Relay Agent Behavior"
   o  Added section "Server Behavior"; moved second paragraph of section
      "Option Semantics and Usage" to "Server Behavior"
   o  Updated reference to draft-ietf-dhc-dhcpv6-srsn-option-00
   o  Clarified descriptions of various option fields in section
      "Encapsulating DHCP options in the RAAN Option"

   Changes in rev -03: refreshed after expiration.

13.  Normative References


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


   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.


              Volz, B. and R. Droms, "DHCPv6 Server Reply Sequence
              Number Option", draft-ietf-dhc-dhcpv6-srsn-option-00 draft-ietf-dhc-dhcpv6-srsn-option-02 (work
              in progress), November 2006. February 2009.

Authors' Addresses

   Ralph Droms
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA  01719

   Phone: +1 978.936.1674
   Email: rdroms@cisco.com
   Bernie Volz
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA  01719

   Phone: +1 978.936.0382
   Email: volz@cisco.com

   Ole Troan
   Cisco Systems, Inc.
   Shinjuku Mitsui Building, 2-1-1, Nishi-Shinjuku, Shinjuku-Ku
   Tokyo, Kanto  163-0409
   No Affiliation

   Phone: +81 3 5324.4027 TBD
   Email: otroan@cisco.com

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