    Network Working Group                                           M. Stapp
    Request for Comments: 4243                                    R. Johnson
    Category: Standards Track                                 T. Palaniappan
                                                         Cisco Systems, Inc.
                                                               December 2005

                 Vendor-Specific Information Suboption for the
         Dynamic Host Configuration Protocol (DHCP) Relay Agent 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.

    Copyright Notice

       Copyright (C) The Internet Society (2005).

    Abstract

       This memo defines a new Vendor-Specific Information suboption for the
       Dynamic Host Configuration Protocol's (DHCP) relay agent information
       option.  The suboption allows a DHCP relay agent to include vendor-
       specific information in the DHCP messages it forwards, as configured
       by its administrator.

    Table of Contents

       1. Introduction ....................................................2
       2. Requirements Terminology ........................................2
       3. The Vendor-Specific Suboption ...................................2
       4. Relay Agent Behavior ............................................4
       5. DHCP Server Behavior ............................................4
       6. Security Considerations .........................................4
       7. IANA Considerations .............................................5
       8. Acknowledgements ................................................5
       Normative References ...............................................5
       Informative References .............................................5

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

    1.  Introduction

       DHCP (RFC 2131 [2]) provides IP addresses and configuration
       information for IPv4 clients.  It includes a relay agent capability,
       in which processes within the network infrastructure receive
       broadcast messages from clients and forward them to DHCP servers as
       unicast messages.  In network environments like DOCSIS data-over-
       cable and xDSL, for example, it has proven useful for the relay agent
       to add information to the DHCP message before forwarding it, using
       the relay agent information option (RFC 3046 [3]).

       Servers that recognize the relay agent option echo it back in their
       replies, and some of the information that relays add may be used to
       help an edge device efficiently return replies to clients.  The
       information that relays supply can also be used in the server's
       decision making about the addresses and configuration parameters that
       the client should receive.

       In many environments, it's desirable to associate some vendor- or
       provider-specific information with the clients' DHCP messages.  This
       is often done using the relay agent information option.  RFC 3046
       defines Remote-ID and Circuit-ID sub-options that are used to carry
       such information.  The values of those suboptions, however, are
       usually based on some network resource, such as an IP address of a
       network access device, an ATM Virtual Circuit identifier, or a DOCSIS
       cable-modem identifier.  As a result, the values carried in these
       suboptions are dependent on the physical network configuration.  The
       Vendor-Specific suboption allows administrators to associate other
       useful data with relayed DHCP messages.

    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 RFC 2119 [1].

    3.  The Vendor-Specific Suboption

       This memo defines a new DHCP relay agent option suboption that
       carries vendor-defined data.  The suboption takes a form similar to
       the Vendor-Identifying, Vendor-Specific Option [7].

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

           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
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |     Code      |    Length     |        Enterprise Number1     |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                               |  DataLen1     |               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
          \                         Suboption Data1                       \
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                      Enterprise Number2                       |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |  DataLen2     |             Suboption Data2                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          \                                                               \
          .                                                               .
          .                                                               .
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       The Code for the suboption is 9.

       The one-byte Length field is the length of the data carried in the
       suboption, in bytes.  The length includes the length of the first
       Enterprise Number; the minimum length is 4 bytes.

       "Enterprise NumberN" is a vendor's Enterprise Number as registered
       with IANA [4].  It is a four-byte integer value in network byte-
       order.

       DataLenN is the length of the data associated with the Enterprise
       Number.

       The Suboption Data is an opaque sequence of bytes.

       The Vendor-Specific suboption includes at least one Enterprise Number
       and carries opaque data defined by the organization identified by the
       Enterprise Number.  A relay may include data associated with more
       than one vendor's Enterprise Number within a single instance of the
       Suboption.

       Of course, the Vendor-Specific data are vendor-specific.  This
       specification does not establish any requirements on the data in the
       suboption.  Vendors who make use of this suboption are encouraged to
       document their usage in order to make interoperability possible.

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

    4.  Relay Agent Behavior

       DHCP relay agents MAY be configured to include Vendor-Specific
       suboptions if they include a relay agent information option in
       relayed DHCP messages.  The suboptions' types and data are assigned
       and configured through mechanisms that are outside the scope of this
       memo.

       Relay implementors are encouraged to offer their administrators a
       means of configuring what data can be included in this suboption, and
       to document what they are capable of.

    5.  DHCP Server Behavior

       This suboption provides additional information to the DHCP server.
       The DHCP server, if it is configured to support this suboption, may
       use this information, in addition to other relay agent option data
       and other options included in the DHCP client messages, in order to
       assign an IP address and/or other configuration parameters to the
       client.  There is no special additional processing for this
       suboption.

    6.  Security Considerations

       Message authentication in DHCP for intradomain use, where the out-
       of-band exchange of a shared secret is feasible, is defined in RFC
       3118 [5].  Potential exposures to attack are discussed in section 7
       of the DHCP protocol specification in RFC 2131 [2].

       The DHCP relay agent option depends on a trusted relationship between
       the DHCP relay agent and the server, as described in section 5 of RFC
       3046.  Fraudulent relay agent option data could potentially lead to
       theft-of-service or exhaustion of limited resources (like IP
       addresses) by unauthorized clients.  A host that tampered with relay
       agent data associated with another host's DHCP messages could deny
       service to that host, or interfere with its operation by leading the
       DHCP server to assign it inappropriate configuration parameters.

       While the introduction of fraudulent relay agent options can be
       prevented by a perimeter defense that blocks these options unless the
       relay agent is trusted, a deeper defense using authentication for
       relay agent options via the Authentication Suboption [6] SHOULD be
       deployed as well.

       There are several data in a DHCP message that convey information that
       may identify an individual host on the network.  These include the
       chaddr, the client-id option, and the hostname and client-fqdn
       options.  Depending on the type of data included, the Vendor-Specific
       suboption may also convey information that identifies a specific host
       or a specific user on the network.  In practice, this information
       isn't exposed outside the internal service-provider network, where
       DHCP messages are usually confined.  Administrators who configure
       data that will be used in DHCP Vendor-Specific suboptions should be
       careful to use data that are appropriate for the types of networks

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

       they administer.  If DHCP messages travel outside the service-
       provider's own network, or if the suboption values may become visible
       to other users, it may raise privacy concerns for the access provider
       or service provider.

    7.  IANA Considerations

       The IANA has assigned the suboption number 9 for the Vendor-Specific
       Information Suboption from the DHCP Relay Agent Information Option
       [3] suboption number space.

    8.  Acknowledgements

       The authors are grateful to Andy Sudduth, Josh Littlefield, and Kim
       Kinnear for their review and comments.

    Normative References

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

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

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

       [4]  IANA, "Private Enterprise Numbers (http://www.iana.org/
            assignments/enterprise-numbers.html)".

    Informative References

       [5]  Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
            RFC 3118, June 2001.

       [6]  Stapp, M. and T. Lemon, "The Authentication Suboption for the
            Dynamic Host Configuration Protocol (DHCP) Relay Agent Option",
            RFC 4030, March 2005.

       [7]  Littlefield, J., "Vendor-Identifying Vendor Options for Dynamic
            Host Configuration Protocol version 4 (DHCPv4)", RFC 3925,
            October 2004.

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

    Authors' Addresses

       Mark Stapp
       Cisco Systems, Inc.
       1414 Massachusetts Ave.
       Boxborough, MA  01719
       USA

       Phone: 978.936.0000
       EMail: mjs@cisco.com

       Richard Johnson
       Cisco Systems, Inc.
       170 W. Tasman Dr.
       San Jose, CA  95134
       USA

       Phone: 408.526.4000
       EMail: raj@cisco.com

       Theyn Palaniappan
       Cisco Systems, Inc.
       170 W. Tasman Dr.
       San Jose, CA  95134
       USA

       Phone: 408.526.4000
       EMail: athenmoz@cisco.com

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    RFC 4243            Vendor-Specific Relay Suboption        December 2005

    Full Copyright Statement

       Copyright (C) The Internet Society (2005).

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    Acknowledgement

       Funding for the RFC Editor function is currently provided by the
       Internet Society.

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