One document matched: draft-zhao-dhc-user-authentication-00.txt




DHC Working Group                                              Amy. Zhao
Internet-Draft                               Huawei Technologies Co.,Ltd
Expires: March 26, 2007                               September 22, 2006


                     DHCP User-based Authentication
                 draft-zhao-dhc-user-authentication-00

Status of this Memo

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   This Internet-Draft will expire on March 26, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines an authentication mechanism to provide an
   authentication for a user in an access network by means of dhcp.  The
   authentication mechanism described here couples DHCP to an
   authentication, authorization and accounting system (AAA), thus
   enabling users to supply user credentials for AAA via DHCP.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Terminology . . . . . . . . . . . . . . . . . . .  5
   3.  Basic Authentication . . . . . . . . . . . . . . . . . . . . .  6
   4.  Digest Authentication  . . . . . . . . . . . . . . . . . . . .  8
   5.  DHCPv4 Options . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  User-based Authentication Option . . . . . . . . . . . . . 11
       5.1.1.  Option Format  . . . . . . . . . . . . . . . . . . . . 11
       5.1.2.  Digest authentication Format . . . . . . . . . . . . . 12
     5.2.  Relay Agent User-based authentication sub-option . . . . . 13
       5.2.1.  Sub-option Format  . . . . . . . . . . . . . . . . . . 13
       5.2.2.  digest authentication format . . . . . . . . . . . . . 14
   6.  DHCP Client Behavior . . . . . . . . . . . . . . . . . . . . . 16
   7.  DHCP Relay Agent Behavior  . . . . . . . . . . . . . . . . . . 17
   8.  DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 18
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     12.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
   Intellectual Property and Copyright Statements . . . . . . . . . . 24



























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1.  Introduction

   Traditionally ,DHCP has mainly been used in private domains.
   Howerver, in public domain environments, the DHCP protocol will be
   used between a user-equipment and a DHCP Server which is inside the
   Access Network and possibly several routers away from the Access
   Router, such as NAS.  Network service offered via this access network
   mainly need user identification instead of equipment identification,
   therefore, the DHCP required a user-based authenticaiton.

   An authentication mechanism for DHCPv4 protocol messages was
   developed in [RFC3118].This allows DHCP clients and servers to
   authenticate each other.  Our purpose differs in that we want to
   authenticate and authorize a user before he accesses a provider
   network, to apply policy to customize this access connection to
   account for the service.

   As [I-D.dhcv4-treat-analysis] pointed out that [RFC3118] is concerned
   specifically with DHCP clients and servers authenticating themselves
   to each other if required by an administrative domain.  This is not
   the same thing as authenticating users for establishing their
   Identity, access rights, permissions, or other matters relating to
   what they can view or do once connected to the network.  Only one
   mechanism is not sufficient and a well-secured network needs both.

   Consider the following architecture:
                                                            +--------+
                                            AAA Protocol    | AAA    |
                                      +---------------------+ Server |
                                      |                     +--------+
                                      |
                                      |
           +--------+         +-------+-------+              +--------+
           | DHCP   |  DHCP   | NAS/DHCP Relay|    DHCP      | DHCP   |
           | Client |---------| /AAA Client   |--------------| Server |
           +--------+         +---------------+              +--------+

                            Figure 1: Referenced Architecture


   In some access network enviornments, a Network Access Server(NAS)
   enabling authenticated network access acts as a DHCP relay agent to
   forward requests and responses between the access client and a DHCP
   server within the network.  We proposes in this document that the
   NAS, acting as a DHCP relay agent and a AAA client, be used as AAA
   triggers intercepting and conveying relevant information from clients
   to AAA servers.




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   The interface between AAA server and NAS is out of the scope of this
   document.

















































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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 [RFC2119].

   Definitions for terms and acronyms used in this document are defined
   in [RFC2131] .











































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3.  Basic Authentication

   In basic authentication, DHCP client inserts the username and
   password in clear text into the DHCP request message.  The NAS,
   acting as DHCP relay agent and AAA client at the same time, extracts
   the username/password information from request message, and sends
   this information to AAA server for user authentication.  If
   authenticated successfully, NAS relays the request message to DHCP
   Server.

   The following is an example of message flow (Success):

   Client          Relay/AAA Client         AAA Server      DHCP Server
   ------          ----------------         -----------     -----------
    | Discover{username |                       |                 |
    | password}         | Auth Request{username |                 |
    | ----------------> | Password}             |                 |
    |                   | --------------------> |                 |
    |                   | Auth Response{success}|                 |
    |                   | <-------------------- |                 |
    |                   |                  Discover               |
    |                   | --------------------------------------->|
    |                   |                    Offer                |
    |        Offer      | <---------------------------------------|
    | <---------------- |                       |                 |
    |        Request    |                       |                 |
    | ----------------> |                   Request               |
    |                   | --------------------------------------->|
    |                   |                     Ack                 |
    |        Ack        | <-------------------------------------- |
    | <---------------- |                       |                 |
    |                   |                       |                 |

         Figure 2: Basic Authentication example

   1.  The client sends DHCPDISCOVER message by inserting the username
       into User-Class option and the password into User-base
       Authentication option.

   2.  Upon receiving the DHCPDISCOVER message,Relay agent extracts the
       username and password, then supplies the username/password
       information to AAA Server by sending Auth Request message.

   3.  AAA server response with Auth Success Response.

   4.  Relay Agent forwards the DHCPDISCOVER message to DHCP Server by
       inserting the authentication result into Relay agent user-based
       authentication sub-option.



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   5.  Upon receiveing forwarded DHCPDISCOVER message with successful
       authentication result in Relay agent user-based authentication
       sub-option, DHCP Server reponses with DHCP OFFER.

   The mechanism is not considered to be a secure method of user
   authentication, as the user name and password are passed over the
   network as cleartext.












































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4.  Digest Authentication

   In digest authentication, user's password is not sent in clear-text.
   The digest authentication is based on a simple challenge-response
   paradigm and uses a server-specified nonce to seed the generation of
   the digest value.  The user retrieves the nonce and calculates a
   digest(by default, the HMAC-MD5 digest) of the password, the
   retrieved nonce value.  In this way, the password is never sent in
   the clear..

   This document defines the use of a particular technique based on the
   HMAC protocol[RFC2104] using the MD5 hash[RFC1321].

   The following is an example of message flow (Success):

   Client        Relay/AAA Client          AAA Server       DHCP Server
   ------        ----------------          -----------      -----------
    | Discover{username}|                       |                 |
    | ----------------> | Challenge Request     |                 |
    |                   | {usename}             |                 |
    |                   | --------------------> |                 |
    |                   | Challenge Response    |                 |
    |                   | {username,Nonce}      |                 |
    |                   | <-------------------- |                 |
    |                   |        Discover{Nonce,username}         |
    |                   | --------------------------------------->|
    | Offer{username    |         Offer{Nonce,username}           |
    | Nonce}            | <---------------------------------------|
    | <---------------- |                       |                 |
    | Request{username, |                       |                 |
    | Nonce,encrypted   |                       |                 |
    | password}         | Auth Request{username,|                 |
    | ----------------> |  Nonce,encrypted      |                 |
    |                   |  password}            |                 |
    |                   | --------------------> |                 |
    |                   | Auth Response{success}|                 |
    |                   | <-------------------- |                 |
    |                   |                   Request               |
    |                   | --------------------------------------->|
    |                   |                     Ack                 |
    |        Ack        | <-------------------------------------- |
    | <---------------- |                       |                 |
    |                   |                       |                 |

                     Figure 3: Digest Authentication example






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   1.   The client sends DHCP DISCOVER message by inserting the username
        into User-Class option.

   2.   Upon receiving the DHCPDISCOVER message , relay agent extracts
        the username, then sends challenge request to AAA server with
        username.

   3.   AAA server response Challenge Response with a challenge value .

   4.   Relay Agent forwards the DHCPDISCOVER message to DHCP Server by
        inserting the retrieved challenge value into Relay Agent User-
        based Authentication sub-option.

   5.   Upon receiving the forwarded DHCP DISCOVER message, DHCP Server
        extracts the challenge value from Relay Agent User-based
        Authentication sub-option and reponses with a DHCP OFFER by
        inserting the challenge to the User-based Authentication option.

   6.   Relay Agent forwards the DHCP OFFER to the client.

   7.   Upon receiving the forwarded DHCP OFFER, client extracts the
        challenge value from user-based authentication option and
        calculates the digest with the user's password and the challenge
        value, then sends the DHCPREQUEST by inserting username into
        User-Class option and digest password into User-based
        Authentication option.

   8.   Upon receiving DHCPREQUEST, Relay agent extracts the username,
        digest password and challenge value ,then supplies the username/
        digest password/challenge value information to AAA Server by
        sending Auth Request message.

   9.   AAA server response with Auth Succes Response.

   10.  Relay Agent forwards the DHCPREQUEST message to DHCP Server by
        inserting the authentication result into Relay agent user-based
        authentication sub-option.

   11.  Upon receiving forwarded DHCPREQUEST message with successful
        authentication in Relay agent user-based authentication sub-
        option, DHCP Server responses with DHCP ACK.

   Rapid commit, defined by[RFC4039] , specifies how a two-message
   exchange between client and server can dramatically decrease the
   elapsed time for address assignment, a feature becoming significant
   as more and more highly mobile devices desire an abbreviated address
   assignment phase for short duration communications.  Therefore, the
   User-based Digest Authentication simply cannot be used as the



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   DHCPOFFER message required to return a nonce value to the client is
   not present.

   The Digest authentication mechanism described here is a replacement
   for Basic authentication and nothing more.  It is not as secure as
   Kerberos, and not as secure as any client-side private-key mechanism.
   Nevertheless it is better than nothing, and better than Basic
   authentication.











































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5.  DHCPv4 Options

5.1.  User-based Authentication Option

5.1.1.  Option Format

   The format of the DHCPv4 User-based Authentication 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Code      |    Length     |  Protocol     |   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |           User-based Authentication Information               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 4: User-based Authentication Option Format


   Code

      TBD

   length

      contains the length of the protocol,algorithm and user-based
      authentication Information fields in octets.

   Protocol

      defines the particular technique for user-authentication used in
      the option.

      Basic Authentication = 0

      Digest Authentication = 1

   Algorithm

      defines the specific algorithm within the technique identified by
      the protocol field.

      HMAC-MD5 = 1 (specific to Digest Authentication)






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   User-based Authentication Information

      The authentication information, as specified by the protocol and
      algorithm used in this user-authentication option

5.1.2.  Digest authentication Format

   The format of the user-authentication request in a DHCPDISCOVER
   message for digest authentication is:

       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     |0 0 0 0 0 0 0 1|   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the user-authentication information in a DHCPOFFER for
   digest authentication is:

       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     |0 0 0 0 0 0 0 1|   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                  Nonce                                        ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the user-authentication information in a DHCPREQUEST/
   DHCPACK for a digest authentication is:




















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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     |0 0 0 0 0 0 0 1|   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                  Nonce                                        ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                   Digest                                      ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Nonce

      a random value which is used by HMAC-MD5

   Digest

      the result by using the Digest generating function HMAC-MD5.

   The sender computes the Digest using the HMAC[RFC2104] generation
   algorithm and the MD5[RFC1321] hash function.  The password including
   is used as input to the HMAC-MD5 computation function.  The 'nonce'
   field MUST be set to the random value used to generate the Digest.

   Algorithm 1 specifies the use of HMAC-MD5.  Use of a different
   technique, such as HMAC-SHA, will be specified as a separate
   algorithm.

5.2.  Relay Agent User-based authentication sub-option

5.2.1.  Sub-option Format

   In digest authentication mechanism, NAS uses this suboption to carry
   the challenge value or the authentication result to DHCP server.

   This sub-option is a new suboption for the DHCP Relay Agent
   Information option.











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   The format of the relay agent user-based sub-option is as follows:
       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     |    type       |    data       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                 data                                          ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 5: User-based authentication sub-option Format

   Code

      TBD

   length

      the suboption length.

   type

      define the type of the data field

      0 ----- authentication result

      1 ----- random challenge value

   data

      if type =1, this field contains the authentication result

      0 ----- FAILURE

      1 ----- SUCCESS

      if type =2, this field contains a random challenge value

5.2.2.  digest authentication format

   The format of the Relay Agent user-authentication information in a
   DHCPOFFER for digest authentication is:










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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     |0 0 0 0 0 0 0 1|  challenge    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                        challenge                              ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the user-authentication information in a DHCPREQUEST
   for digest authentication is:

       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     |0 0 0 0 0 0 0 0|  result       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



































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6.  DHCP Client Behavior

   The username and password are provided by the user at the beginning
   of the DHCP.

   The DHCP client SHOUD inserts the username in the User-Class
   option[RFC3004].  The username SHOULD be in the form of a Network
   Access Identifier (NAI) [RFC2486] .

   In basic authentication mechanism:

   o  The client MUST include the User-based Authentication option in
      its request message by setting the Protocol field to 0 ,algorithm
      field to 0 and User-based Authentication information fields to the
      password,which is provided by user.

   o  If the received response message does not include the User-based
      Authentication option, the DHCP client SHOULD ignore the received
      message.

   In digest authentication mechanism:

   o  The client MUST include the User-based Authentication option in
      its DHCPDISCOVER message by setting protocol field to 1 .

   o  If the client receives a DHCPOFFER message including the User-
      based Authentication option, it extracts the challenge value from
      the nonce field of the User-based Authentication option, else the
      client SHOULD ignore the DHCPOFFER.

   o  The client compute the digest using HMAC-MD5, with password and
      challenge value as input parameters.

   o  The client replies with a DHCPREQUEST that MUST include User-based
      Authentication information by setting the digest field to the
      computed digest value .

   o  If the client receives a DHCPACK message without the User-based
      Authentication option, it SHOULD ignore the DHCPACK.












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7.  DHCP Relay Agent Behavior

   In basic authentication mechanism.

   o  The relay agent extracts the password from the User-based
      Authentication option and the user-name from user-class option.

   o  The relay agent, acting as an AAA client at the same time,
      supplies the user-name/password information to AAA server for
      authentication and receives the authentication result from AAA
      server.

   o  The relay agent forwards the authentication result to DHCP server
      by insert the result into the relay agent user-based
      authentication sub-option.

   In digest authentication mechanism:

   o  The relay agent,acting as AAA client at the same time, gets a
      challenge value from AAA server or generates the challenge value
      by itself.

   o  The relay agent forwards the challenge value to DHCP server to the
      DHCP server by inserting the challenge value into the relay agent
      user-based authentication sub-option of DHCPDISCOVER .

   o  Upon receiving DHCPREQUEST, the relay agent extracts the digest
      password and the challenge value from the User-based
      authentication option, the username from the user-class option.

   o  The relay agent, acting as an AAA client at the same time,
      supplies the user-name/the digest password/challenge value
      information to AAA server for authentication and receives the
      authentication result from AAA server

   o  The relay agent forwards the authentication result to DHCP server
      by inserting the result into the relay agent user-based
      authentication sub-option













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8.  DHCP Server Behavior

   If the received request message is included the User-based
   Authentication option, the DHCP Server SHOULD includes the User-based
   Authentication option in the response message.

   In basic authentication mechanism:

   o  If the authentication result in the relay agent user-based
      authentication sub-option is SUCCESS, The DHCP Server handles the
      request message from the DHCP client according to [RFC2131]

   o  Otherwise, the DHCP Server replies with DHCPNAK for DHCPREQUEST.

   In digest authentication mechanism:

   o  Upon receiving a relayed DHCPDISCOVER message, DHCP server
      extracts the challenge value from the relay agent user-based
      authentication sub-option .

   o  The DHCP server replies with a DHCPOFFER message by inserting the
      challenge value into the user-based Authentication option.

   o  Upon receiving a relayed DHCPREQUEST message

      *  If previous received DHCPDISCOVER includes a User-based
         Authentication option, and the received DHCPREQUEST message
         does not include a User-based Authentication option, DHCP
         Server SHOULD ignore the DHCPREQUEST message.

      *  If the authentication result in the relay agent user-based
         authentication sub-option is FAILURE, DHCP server replies with
         DHCPNAK.


















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9.  Security Considerations

   In basic authentication mechanism and digest authentication
   mechanism, there is a delay between request and response message.If
   the delay is too long ,it will affect the client state machine and
   results in retransmission of request message.

   The transport of the user-based authentication between the AAA
   infrastructure and the NAS is subject to the standard RADIUS and
   Diameter security consideration.  No new security consideration are
   imposed by the usage of this document.  The security mechanisms
   provided by [RFC2865] and [RFC3588] are applicable and provide
   adequate security for this purpose.

   The communication between the NAS/DHCP relay agent and the DHCP
   server must be authenticated, integrity and replay protected.



































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10.  IANA Considerations

   IANA is requested to allocate DHCPv4 option code and DHCPv4 Relay
   agent sub-option for this purpose.















































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11.  Acknowledgements


















































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12.  References

12.1.  Normative References

   [RFC1321]  Rivest, R., "HMAC: The MD5 Message-Digest Algorithm",
              RFC 1321, April 1992.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC2486]  Aboba, B. and M. Beadles, "The Network Access Identifier",
              RFC 2486, January 1999.

   [RFC3004]  Stump, G., Droms, R., and Y. Gu, "The User Class Option
              for DHCP", RFC 3004, November 2000.

   [RFC3118]  Droms, R. and W. Arbaugh, "Authentication for DHCP
              Messages", RFC 3118, June 2001.

12.2.  Informative References

   [I-D.dhcv4-treat-analysis]
              Hibbs, R., Smith, C., Volz, B., and M. Zohar, "Dynamic
              Host Configuration Protocol for IPv4 (DHCPv4) Threat
              Analysis",  draft-ietf-dhc-v4-threat-analysis-03 (work in
              progress), June 2006.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC4039]  Park, S., Kim, P., and B. Volz, "Rapid Commit Option for
              the Dynamic Host Configuration Protocol version 4
              (DHCPv4)", RFC 4039, March 2005.







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Author's Address

   Yuping Zhao
   Huawei Technologies Co.,Ltd
   Huihong Mansion,No.91 Baixia Rd.
   Nanjing, Jiangsu  210001
   P.R.China

   Phone: +86(25)84565403
   Email: zhaoyuping@huawei.com









































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PAFTECH AB 2003-20262026-04-24 02:46:36