DHC Working Group                                               M. Stapp
Internet-Draft                                                R. Johnson
Expires: February 7, 2005                                 T. Palaniappan
                                                     Cisco Systems, Inc.
                                                          August 9, 2004

 Vendor-Specific Information Suboption for the DHCP Relay Agent Option

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.


   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 DHCP messages it forwards, as
   configured by its administrator.

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Table of Contents

   1. Requirements Terminology . . . . . . . . . . . . . . . . . . . . 3
   2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3. The Vendor-Specific Suboption  . . . . . . . . . . . . . . . . . 3
   4. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . . . 4
   5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . . 5
   6. Security Considerations  . . . . . . . . . . . . . . . . . . . . 5
   7. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 6
   8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
      Normative References . . . . . . . . . . . . . . . . . . . . . . 7
      Informative References . . . . . . . . . . . . . . . . . . . . . 7
      Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
      Intellectual Property and Copyright Statements . . . . . . . . . 9

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1. Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

2. 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 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.

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 [8].

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       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 <TBD> (to be assigned by IANA).

   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

   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

   The Vendor-Specific data are of course provider-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.

4. Relay Agent Behavior

   DHCP relay agents MAY be configured to include Vendor-Specific
   suboptions if they include a relay agent information option in

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   relayed DHCP messages. The suboptions' types and data are assigned
   and configured through mechanisms that are outside the scope of this

   Relay implementors are encouraged to offer their administrators some
   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.

   DHCP server vendors are encouraged to offer their administrators some
   means of configuring the use of data from incoming Vendor-Specific
   suboptions in DHCP decision-making.

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] or IPSEC [7]
   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

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   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's going to be used in DHCP Vendor-Specific suboptions should be
   careful to use data that are appropriate for the types of networks
   they administer. If DHCP messages travel outside the
   service-provider's own network, or if the suboption values may become
   visible to other users, that may raise privacy concerns for the
   access provider or service provider.

7. IANA Considerations

   IANA is requested to assign a suboption number 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.

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Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", 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/

Informative References

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

   [6]  Stapp, M., "The Authentication Suboption for the DHCP Relay
        Agent Option", draft-ietf-dhc-auth-suboption-04.txt  (work in
        progress), October 2003.

   [7]  Droms, R., "Authentication of Relay Agent Options Using IPsec",
        draft-ietf-dhc-relay-agent-ipsec-01.txt  (work in progress),
        November 2003.

   [8]  Littlefield, J., "Vendor-Identifying Vendor Options for DHCPv4",
        draft-ietf-dhc-vendor-03.txt  (work in progress), June 2004.

Authors' Addresses

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

   Phone: 978.936.0000
   EMail: mjs@cisco.com

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

   Phone: 408.526.4000
   EMail: raj@cisco.com

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

   Phone: 408.526.4000
   EMail: athenmoz@cisco.com

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