DHCPv6 Relay Agent Echo Request Option
RFC 4994

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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

Zeng, et al.                Standards Track                     [Page 1]
RFC 4994                    Relay Agent ERO               September 2007

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.

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    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+