Network Working Group                                            S. Zeng
Request for Comments: 4994                                       B. Volz
Category: Standards Track                                     K. Kinnear
                                                    Cisco Systems, Inc.
                                                          J. Brzozowski
                                                          Comcast Cable
                                                         September 2007


                DHCPv6 Relay Agent Echo Request Option

Status of This Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Abstract

  This memo defines a Relay Agent Echo Request option for the Dynamic
  Host Configuration Protocol for IPv6 (DHCPv6).  The option allows a
  DHCPv6 relay agent to request a list of relay agent options that the
  server echoes back to the relay agent.

Table of Contents

  1. Introduction ....................................................2
  2. Requirements Terminology ........................................2
  3. The Relay Agent Echo Request Option .............................2
  4. DHCPv6 Relay Agent Behavior .....................................3
  5. DHCPv6 Server Behavior ..........................................3
  6. Security Considerations .........................................4
  7. IANA Considerations .............................................4
  8. Acknowledgements ................................................4
  9. References ......................................................4
     9.1. Normative References .......................................4
     9.2. Informative References .....................................4












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1.  Introduction

  DHCPv6 [2] provides a framework for configuring IPv6 clients with
  addresses and other network parameters.  It includes a relay agent
  capability.  A relay agent is an intermediary node that delivers DHCP
  messages between clients and servers.  The relay agent and the server
  exchange information using options in relay agent messages.  The
  relay agent may add relay agent options to the client DHCP message
  before forwarding it.

  The information that relay agents supply can be used in the server's
  decision making about the addresses, delegated prefixes, and
  configuration parameters that the client is to receive.  Likewise,
  the relay may need some of the information to efficiently return
  replies to clients.

  In DHCPv4, the server generally echoes the relay agent option back
  verbatim to the relay agent in server-to-client replies [3].
  However, DHCPv6 [2] does not require the server to do so.  This could
  be problematic, as the relay agent may need to use some relay options
  even if the server does not recognize them.

  This memo defines a relay agent echo request option that the relay
  agent uses to explicitly request a list of options that the server
  echoes back to the relay agent.

2.  Requirements Terminology

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in [1].

3.  The Relay Agent Echo Request Option

  The relay agent adds options in the Relay Forward message that the
  server uses to guide its decision making with regard to address
  assignment, prefix delegation, and configuration parameters.  The
  relay agent also knows which of these options that it will need to
  efficiently return replies to the client.  It uses the relay agent
  Echo Request option to inform the server of the list of relay agent
  options that the server must echo back.










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  The format of the DHCPv6 Relay Agent Echo Request option is shown
  below:

   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_ERO          |           option-len          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    requested-option-code-1    |    requested-option-code-2    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                              ...                              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  option-code              OPTION_ERO (43).
  option-len               2 * number of requested options.
  requested-option-code-n  The option code for an option requested by
                           the relay agent.

4.  DHCPv6 Relay Agent Behavior

  A relay agent MAY include an Echo Request option in a Relay Forward
  message to inform the server about options the relay agent wants the
  server to echo back to the relay agent.  If the relay agent takes
  different actions based on whether an option is echoed back or not,
  then the relay agent SHOULD NOT include such an option in the Echo
  Request option.  Note that the relay uses the OPTION_ORO [2] to
  request the server to return options (e.g., [4]) other than relay
  agent options in the Relay Forward message.

5.  DHCPv6 Server Behavior

  When a server creates a Relay-Reply, it SHOULD perform ERO processing
  after processing the ORO and other options processing.  For each
  option in the ERO:

  a.  If the option is already in the Relay-Reply, the server MUST
      ignore that option and continue to process any remaining options
      in the ERO.

  b.  If the option was not in the received Relay-Forward, the server
      MUST ignore that option and continue to process any remaining
      options in the ERO.

  c.  Otherwise, the server MUST copy the option, verbatim, from the
      received Relay-Forward to the Relay-Reply, even if the server
      does not otherwise recognize that option.





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6.  Security Considerations

  As the Echo Request option is only exchanged between relay agents and
  DHCPv6 servers, section 21.1 of [2] provides details on securing
  DHCPv6 messages sent between servers and relay agents.  And, section
  23 of [2] provides general DHCPv6 security considerations.

7.  IANA Considerations

  IANA has assigned a DHCPv6 option code for the OPTION_ERO (Relay
  Agent Echo Request) Option (43).

8.  Acknowledgements

  Thanks to Ralph Droms, Josh Littlefield, Richard Johnson, and Hemant
  Singh for their consistent input, ideas, and review during the
  production of this document.

9.  References

9.1.  Normative References

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

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

  [3]  Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
       January 2001.

9.2.  Informative References

  [4]  Droms, R., Volz, B., and O. Troan, "DHCPv6 Relay Agent
       Assignment Notification (RAAN) Option", Work in Progress,
       November 2006.














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Authors' Addresses

  Shengyou Zeng
  Cisco Systems, Inc.
  1414 Massachusetts Ave.
  Boxborough, MA  01719
  USA

  Phone: +1 978 936 0000
  EMail: [email protected]


  Bernard Volz
  Cisco Systems, Inc.
  1414 Massachusetts Ave.
  Boxborough, MA  01719
  USA

  Phone: +1 978 936 0000
  EMail: [email protected]


  Kim Kinnear
  Cisco Systems, Inc.
  1414 Massachusetts Ave.
  Boxborough, MA  01719
  USA

  Phone: +1 978 936 0000
  EMail: [email protected]


  John Jason Brzozowski
  Comcast Cable
  1800 Bishops Gate Boulevard
  Mt. Laurel, NJ  08054
  USA

  Phone: +1 856 324 2671
  EMail: [email protected]











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