Dynamic Host Configuration Protocol (DHCP) Options for the Intel Preboot eXecution Environment (PXE)
RFC 4578

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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

Johnston & Venaas            Informational                      [Page 1]
RFC 4578                    DHCP PXE Options               November 2006

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  |
               +----+-----+-----+-----+

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