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Versions: 00 01

DHC Working Group                                               L. Huang
Internet-Draft                                                   H. Deng
Intended status: Informational                              China Mobile
Expires: September 5, 2010                                 March 4, 2010


        DHCP option including Multiple Relay Agents' Information
            draft-huang-dhc-multiple-relay-agents-option-01

Abstract

   RFC 3046 allows only the first Relay Agent to append Relay Agent
   Information option.  In some networks, both Layer 2 Relay Agents and
   Layer 3 Relay Agents are deployed and their information is necessary
   for DHCP packets forwarding and DHCP server's policy designing
   described as [I-D.huang-dhc-relay-ps].  This document defines new
   sub-options for Relay Agent Information option (option 82) and
   describes how multiple relay agents add their information into option
   82.

Status of this Memo

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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  DHCP option including Multiple Relay Agents' Information  . . . 4
     2.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     2.2.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Informative References  . . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9






























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1.  Introduction

   As defined in RFC 3046, Relay Agent Information option is inserted by
   the DHCP relay agent (or downstream network element) when forwarding
   client-originated DHCP packets to a DHCP server.  Servers recognizing
   the Relay Agent Information option may use the information to
   implement IP address or other parameter assignment policies.  The
   DHCP Server echoes the option back to the relay agent in server-to-
   client replies, and the relay agent strips the option before
   forwarding the reply to the client.

   RFC 3046 allows only one agent add its information with option 82.
   But in some scenarios as [I-D.huang-dhc-relay-ps], multiply relay
   agents need to insert more information into the same DHCP message.
   This document defines new sub-options for Relay Agent Information
   option (option 82) and describes how multiple relay agents add their
   information into option 82.


































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2.  DHCP option including Multiple Relay Agents' Information

2.1.  Format

   +-------+-----+-----+
   |Code(x)| Len |Value|
   +-------+-----+-----+

   Sub-option x: Agent ID.  Describe a unique identifier for the agent
   who insert this set of sub-options.

   +-------+-------+
   |Code(y)| Len(0)|
   +-------+-------+

   Sub-option y: Identify the end of information of one device.

2.2.  Mechanism

                                                -------
             +-----------+  +-----------+    ///       \\\    +------+
   +------+  |Layer 2    |  |Layer 3    |   |             |   |DHCP  |
   |Client+--+Relay Agent+--+Relay Agent+--+    Network    +--+Server|
   +------+  +-----------+  +-----------+   |             |   +------+
                                             \\\       ///
                                                -------

   As shown in above figure, it's a most popular network scenario where
   option including Multiple Relay Agents' Information is necessary.
   Based on the demand as [I-D.huang-dhc-relay-ps], agents work as
   following:

   (1) An initiating client sends a DHCP discovery packet.

   (2) Layer 2 relay agent receives the discovery packet without option
   82.  So it inserts an option 82 as [RFC3046].  After that, the
   discovery packet is forwarded to the appropriate port.

   (3) Layer 3 relay agent receives the discovery packet and check out
   that it already contains an option 82.  Firstly it adds an sub-option
   y defined in section 2.2 into the existing option 82 following sub-
   options added by layer 2 agent.  And then it adds its agent ID sub-
   option(x), circuit ID sub-option and end ID sub-option(y) into the
   existing option 82.  After that, the discovery packet is forwarded
   and reaches DHCP server directly or through a network.

   (4) DHCP server handles the discovery packet and could carry out
   flexible IP assigning or other policies based on the information of



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   option 82 described in this document.  After that DHCP server reply a
   DHCP response packet containing the original option 82 carried in the
   corresponding discovery packet.

   (5) Layer 3 relay agents quickly get the right outgoing interface
   based on the information in the option 82 and forward the response
   packet after deleting sub-options it added before.

   (6) Layer 2 relay agents quickly get the right outgoing interface
   based on the information in the option 82 and forward the response
   packet.  Layer 2 relay agent deletes the whole option 82 before
   forwarding the packet.

   If there are more relay agents between Layer 2 and Layer 3 relay
   agent or between Layer 3 relay agent and DHCP server, the third and
   the following relay agents could only add their agent ID sub-
   option(x), circuit ID sub-option and end ID sub-option(y) into the
   existing option 82 before forwarding the discovery packet upward.
   The processing of replay packet from DHCP server to client is similar
   as above.































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3.  Security Considerations

   This document doesn't propose any new protocol.
















































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4.  IANA Considerations

   This document requires new numbers for sub-option code x and y
   described in section 2.1.















































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5.  Informative References

   [I-D.huang-dhc-relay-ps]
              Huang, L., Deng, H., Kurapati, P., and B. Joshi, "Problem
              Statement for DHCP Relay Agent",
              draft-huang-dhc-relay-ps-00 (work in progress), July 2009.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, January 2001.




































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Authors' Addresses

   Lu Huang
   China Mobile
   Unit2, 28 Xuanwumenxi Ave,Xuanwu District
   Beijing 100053
   China

   Email: huanglu@chinamobile.com


   Hui Deng
   China Mobile
   Unit2, 28 Xuanwumenxi Ave,Xuanwu District
   Beijing 100053
   China

   Email: denghui@chinamobile.com

































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