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Versions: 00 01 02 03 RFC 4578

Dynamic Host Configuration Working                           M. Johnston
Group                                                  Intel Corporation
Internet-Draft                                            S. Venaas, Ed.
Expires: September 8, 2006                                       UNINETT
                                                           March 7, 2006


     DHCP Options for the Intel Preboot eXecution Environment (PXE)
                     draft-ietf-dhc-pxe-options-03

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   We define DHCP options being used by Preboot eXecution Environment
   (PXE) and Extensible Firmware Interface (EFI) clients to uniquely
   identify booting client machines and their pre-OS runtime environment
   so the DHCP and/or PXE boot server can return the correct OS
   bootstrap image (or pre-boot application) name and server to the
   client.




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Requirements Language

   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].


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Option Definitions  . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Client System Architecture Type Option Definition . . . . . 3
     2.2.  Client Network Interface Identifier Option Definition . . . 4
     2.3.  Client Machine Identifier Option Definition . . . . . . . . 5
     2.4.  Options Requested by PXE Clients  . . . . . . . . . . . . . 5
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8






























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1.  Introduction

   These DHCP [2] options are being widely used by PXE compliant clients
   to uniquely identify booting client machines themselves and their
   pre-OS runtime environment so the DHCP and/or PXE boot server can
   return the correct OS bootstrap image (or pre-boot application) name
   and server to the client.  In the past, this work was done by
   examining the network MAC address in the "chaddr" field in the BOOTP/
   DHCP header and keeping a database of MAC addresses on the BOOTP/DHCP
   server.  This was deemed insufficient for large and complex networks
   for two main reasons. 1) Multiple laptops could end up with the same
   MAC address if the NIC was in a shared docking station. 2) Multiple
   network devices and MAC addresses could be used by one machine for
   redundancy or because of repairs.  Another issue that came up was the
   machine that could change its pre-OS runtime environment.  This issue
   caused the creation of another new option to identify the runtime
   environment so the correct binary image could be matched up with the
   booting machine.  These options are defined by Intel in the PXE [3]
   and EFI [4] specifications and are being documented in this draft for
   completeness within the IETF.


2.  Option Definitions

   There are three DHCP options [5] defined for use by PXE clients.

2.1.  Client System Architecture Type Option Definition

   The format of the option is:

          Code  Len  16-bit Type
         +----+-----+-----+-----+
         | 93 |  n  | n1  | n2  |
         +----+-----+-----+-----+

   Octet "n" gives the number of octets containing "architecture types"
   (not including the code and len fields).  It MUST be an even number
   greater than zero.  Clients that support more than one architecture
   type MAY include a list of these types in their initial DHCP and PXE
   boot server packets.  The list of supported architecture types MAY be
   reduced in any packet exchange between the client and server(s).
   Octets "n1" and "n2" encode a 16-bit architecture type identifier
   that describes the pre-boot runtime environment(s) of the client
   machine.







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   As of the writing of this document the following pre-boot
   architecture types have been requested.

      Type   Architecture Name
      ----   -----------------
        0    Intel x86PC
        1    NEC/PC98
        2    EFI Itanium
        3    DEC Alpha
        4    Arc x86
        5    Intel Lean Client
        6    EFI IA32

   This option MUST be present in all DHCP and PXE packets sent by PXE
   compliant clients and servers.

2.2.  Client Network Interface Identifier Option Definition

   The format of the option is:

          Code  Len  Type Major Minor
         +----+-----+----+-----+-----+
         | 94 |  3  |  t |  M  |  m  |
         +----+-----+----+-----+-----+

   Octet "t" encodes a network interface type.  For now the only
   supported value is 1 for UNDI (Universal Network Device Interface).
   Octets "M" and "m" describe the interface revision.  To encode the
   UNDI revision of 2.11, "M" would be set to 2 and "m" would be set to
   11 (0x0B).

      Revision  Description
      --------  -----------
      < 2.00    LANDesk service agent boot ROMs.  No PXE APIs.

        2.00    First generation PXE boot ROMs.  (PXENV+)  [3]

        2.01    Second generation PXE boot ROMs.  (!PXE)   [3]

        3.00    32/64-bit UNDI specification.  (Alpha)     [4]
                EFI boot services driver only.  No EFI runtime support.

        3.10    32/64-bit UNDI specification.  (Beta)  [4]
                First generation EFI runtime driver support.

        3.20    32/64-bit UNDI specification.  (Release)  [4]
                Second generation EFI runtime driver support.




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   This option MUST be present in all DHCP and PXE packets sent by PXE
   compliant clients and servers.

2.3.  Client Machine Identifier Option Definition

   The format of the option is:

          Code  Len  Type  Machine Identifier
         +----+-----+----+-----+ . . . +-----+
         | 97 |  n  |  t |     | . . . |     |
         +----+-----+----+-----+ . . . +-----+

   Octet "t" describes the type of the machine identifier in the
   remaining octets in this option. 0 (zero) is the only defined value
   for this octet at the present time and it describes the remaining
   octets as a 16-octet GUID.  Octet "n" is 17 for type 0.  (One
   definition of GUID can be found in Appendix A in the EFI
   specification [efi].)

   This option MUST be present in all DHCP and PXE packets sent by PXE
   compliant clients and servers.

2.4.  Options Requested by PXE Clients

   All compliant PXE clients MUST include a request for DHCP options 128
   through 135 in all DHCP and PXE packets.  The format and contents of
   these options are NOT defined by the PXE specification.  These
   options MAY be present in the DHCP and PXE boot server replies and
   are meant for use by the downloaded network bootstrap programs.
   These options are NOT used by the PXE boot ROMs.

   As options 128-135 are not officially assigned for PXE use (previous
   to November 2004 they were considered site-specific options, [6]),
   use of these option values for PXE may conflict with other uses of
   the same options on the same networks.


3.  Acknowledgements

   The authors thank Bernie Volz for valuable input.


4.  IANA Considerations

   IANA is requested to update the numbering space defined for public
   DHCP options in [7] with references to this document for options 93,
   94 and 97 (currently there are references to [8]), and also mark
   options 128-135 as being used by PXE and reference this document



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   (they are currently marked as being used by PXE, but without
   references).


5.  Security Considerations

   By specifying incorrect values for some of these options a client may
   get access to, and possibly attempt to execute, code intended for
   another platform or client.  This may have security ramifications.
   Also note that these options contain information about a client's
   system architecture and pre-OS runtime environment which is revealed
   to anyone who is able to listen in on DHCP messages sent by the
   client.  This information may be of use to potential attackers.

6.  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]  Henry, M. and M. Johnston, "Preboot Execution Environment (PXE)
        Specification", September 1999,
        <http://www.pix.net/software/pxeboot/archive/pxespec.pdf>.

   [4]  Intel Corp., "Extensible Firmware Interface Specification",
        December 2002, <http://developer.intel.com/technology/efi/
        main_specification.htm>.

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

   [6]  Volz, B., "Reclassifying Dynamic Host Configuration Protocol
        version 4 (DHCPv4) Options", RFC 3942, November 2004.

   [7]  Droms, R., "Procedures and IANA Guidelines for Definition of New
        DHCP Options and Message Types", BCP 43, RFC 2939,
        September 2000.

   [8]  Droms, R., "Unused Dynamic Host Configuration Protocol (DHCP)
        Option Codes", RFC 3679, January 2004.









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Authors' Addresses

   Michael Johnston
   Intel Corporation
   MS. JF1-239 2111 NE 25th Ave.
   Hillsboro, OR  97124
   USA

   Phone: +1 503-264-9703
   Email: michael.johnston@intel.com


   Stig Venaas
   UNINETT
   Trondheim  NO-7465
   Norway

   Email: venaas@uninett.no

































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