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Network Working Group                                            S. ZengRequest for Comments: 4994                                       B. VolzCategory: Standards Track                                     K. Kinnear                                                     Cisco Systems, Inc.                                                           J. Brzozowski                                                           Comcast Cable                                                          September 2007DHCPv6 Relay Agent Echo Request OptionStatus 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 Contents1. Introduction ....................................................22. Requirements Terminology ........................................23. The Relay Agent Echo Request Option .............................24. DHCPv6 Relay Agent Behavior .....................................35. DHCPv6 Server Behavior ..........................................36. Security Considerations .........................................47. IANA Considerations .............................................48. Acknowledgements ................................................49. References ......................................................49.1. Normative References .......................................49.2. Informative References .....................................4Zeng, et al.                Standards Track                     [Page 1]

RFC 4994                    Relay Agent ERO               September 20071.  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.Zeng, et al.                Standards Track                     [Page 2]

RFC 4994                    Relay Agent ERO               September 2007   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.Zeng, et al.                Standards Track                     [Page 3]

RFC 4994                    Relay Agent ERO               September 20076.  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,section23 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.  References9.1.  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.Zeng, et al.                Standards Track                     [Page 4]

RFC 4994                    Relay Agent ERO               September 2007Authors' Addresses   Shengyou Zeng   Cisco Systems, Inc.   1414 Massachusetts Ave.   Boxborough, MA  01719   USA   Phone: +1 978 936 0000   EMail: szeng@cisco.com   Bernard Volz   Cisco Systems, Inc.   1414 Massachusetts Ave.   Boxborough, MA  01719   USA   Phone: +1 978 936 0000   EMail: volz@cisco.com   Kim Kinnear   Cisco Systems, Inc.   1414 Massachusetts Ave.   Boxborough, MA  01719   USA   Phone: +1 978 936 0000   EMail: kkinnear@cisco.com   John Jason Brzozowski   Comcast Cable   1800 Bishops Gate Boulevard   Mt. Laurel, NJ  08054   USA   Phone: +1 856 324 2671   EMail: john_brzozowski@cable.comcast.comZeng, et al.                Standards Track                     [Page 5]

RFC 4994                    Relay Agent ERO               September 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Zeng, et al.                Standards Track                     [Page 6]