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Versions: 00 01

DHC Working Group                                               M. Stapp
Internet-Draft                                                R. Johnson
Expires: July 29, 2004                                    T. Palaniappan
                                                     Cisco Systems, Inc.
                                                        January 29, 2004


       Vendor-Specific Suboption for the DHCP Relay Agent Option
               <draft-stapp-dhc-vendor-suboption-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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   The list of Internet-Draft Shadow Directories can be accessed at
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   This Internet-Draft will expire on July 29, 2004.

Copyright Notice

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

Abstract

   This memo defines a new Vendor-Specific 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
      References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
      References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
      Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
      Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 9





































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1. 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].

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
   many other relay information option suboptions.










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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 Number     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |     Type      |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
      .                                                               .
      .                         Suboption Data                        .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The Code for the suboption is <TBD>.

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

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

   The one-byte Type value can be used to distinguish among a vendor's
   uses of different data in different configurations, or among
   multiple instances of the suboption which carry different types of
   data.

   The Data is an arbitrary sequence of bytes.

   The Vendor-Specific suboption includes an Enterprise Number and
   carries a sequence of bytes. The Type byte can be used to
   distinguish among different types of data if a single relay vendor
   is able to generate different types of suboptions. The Type codes
   are defined by the vendor identified in the Enterprise Number field;
   the Type codes are not IANA-assigned or -managed. A relay MAY
   include more than one Vendor-Specific suboption.

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


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   memo.

   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 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


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   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 has assigned a value of <TBD> from the DHCP Relay Agent
   Information Option[3] suboption codes for the Vendor-Specific
   Suboption described in this document.

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/assignments/enterprise-numbers.html)".

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-02.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.


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



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   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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Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
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Acknowledgement

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



















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