This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.

The following 'Verified' errata have been incorporated in this document: EID 4624
Network Working Group                                        M. Johnston
Request for Comments: 4578                             Intel Corporation
Category: Informational                                   S. Venaas, Ed.
                                                                 UNINETT
                                                           November 2006


      Dynamic Host Configuration Protocol (DHCP) Options for the
               Intel 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 Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................2
   2. Option Definitions ..............................................2
      2.1. Client System Architecture Type Option Definition ..........2
      2.2. Client Network Interface Identifier Option Definition ......3
      2.3. Client Machine Identifier Option Definition ................4
      2.4. Options Requested by PXE Clients ...........................4
   3. Acknowledgements ................................................5
   4. IANA Considerations .............................................5
   5. Security Considerations .........................................5
   6. Normative References ............................................5

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 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 in RFC 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  |
               +----+-----+-----+-----+

   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 x86-64
              8    EFI Xscale
              9    EFI BC

EID 4624 (Verified) is as follows:

Section: 2.1

Original Text:

            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

Corrected Text:

            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 x86-64
              8    EFI Xscale
              9    EFI BC
Notes:
The values for EFI BC and EFI x86-64 should be swapped. UEFI imeplementations use value 7 to report EFI x86-64, not value 9. The IANA registry for DHCPv6 options (http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml#processor-architecture) correctly reflects reality, with values 7 and 9 swapped compared to RFC 4578.
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). 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 in Appendix 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. 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. [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.no Full Copyright Statement Copyright (C) The IETF Trust (2006). This document is subject to the rights, licenses and restrictions contained in BCP 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 in BCP 78 and BCP 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 at http://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.