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Network Working Group                                        M. JohnstonRequest for Comments: 4578                             Intel CorporationCategory: Informational                                   S. Venaas, Ed.                                                                 UNINETT                                                           November 2006Dynamic Host Configuration Protocol (DHCP) Options for theIntel Preboot eXecution Environment (PXE)Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The IETF Trust (2006).Abstract   We define Dynamic Host Configuration Protocol (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 that the DHCP and/or PXE boot   server can return the correct OS bootstrap image (or pre-boot   application) name and server to the client.Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................22. Option Definitions ..............................................22.1. Client System Architecture Type Option Definition ..........22.2. Client Network Interface Identifier Option Definition ......32.3. Client Machine Identifier Option Definition ................42.4. Options Requested by PXE Clients ...........................43. Acknowledgements ................................................54. IANA Considerations .............................................55. Security Considerations .........................................56. Normative References ............................................5Johnston & Venaas            Informational                      [Page 1]

RFC 4578                    DHCP PXE Options               November 20061.  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 that 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 Media Access Code (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 network interface 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   that 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.1.1.  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 inRFC 2119 [1].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  |               +----+-----+-----+-----+Johnston & Venaas            Informational                      [Page 2]

RFC 4578                    DHCP PXE Options               November 2006   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.   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              7    EFI BC              8    EFI Xscale              9    EFI x86-64   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 Universal Network Device Interface (UNDI).   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).Johnston & Venaas            Informational                      [Page 3]

RFC 4578                    DHCP PXE Options               November 2006         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.   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 value defined   for this octet at the present time, and it describes the remaining   octets as a 16-octet Globally Unique Identifier (GUID).  Octet "n" is   17 for type 0.  (One definition of GUID can be found inAppendix A of   the EFI specification [4].)   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.Johnston & Venaas            Informational                      [Page 4]

RFC 4578                    DHCP PXE Options               November 2006   As options 128-135 are not officially assigned for PXE use (before   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 has updated the numbering space defined for public DHCP options   in [7] with references to this document for options 93, 94, and 97   (previously, there were references to [8]).  Also, IANA marked   options 128-135 as being used by PXE and referenced this document.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 that 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.Johnston & Venaas            Informational                      [Page 5]

RFC 4578                    DHCP PXE Options               November 2006   [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.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.noJohnston & Venaas            Informational                      [Page 6]

RFC 4578                    DHCP PXE Options               November 2006Full Copyright Statement   Copyright (C) The IETF Trust (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST,   AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT   THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY   IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR   PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Johnston & Venaas            Informational                      [Page 7]