Dynamic Host Configuration Protocol Options Used by PXELINUX
RFC 5071

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Network Working Group                                         D. Hankins
Request for Comments: 5071                                           ISC
Category: Informational                                    December 2007

      Dynamic Host Configuration Protocol Options Used by PXELINUX

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.

Abstract

   This document describes the use by PXELINUX of some DHCP Option Codes
   numbering from 208-211.

Hankins                      Informational                      [Page 1]
RFC 5071                    PXELINUX Options               December 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  MAGIC Option . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Description  . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Packet Format  . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  5
     3.4.  Response to RFC 3942 . . . . . . . . . . . . . . . . . . .  5
   4.  Configuration File Option  . . . . . . . . . . . . . . . . . .  5
     4.1.  Description  . . . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Packet Format  . . . . . . . . . . . . . . . . . . . . . .  6
     4.3.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  6
     4.4.  Response to RFC 3942 . . . . . . . . . . . . . . . . . . .  6
     4.5.  Client and Server Behaviour  . . . . . . . . . . . . . . .  6
   5.  Path Prefix Option . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Description  . . . . . . . . . . . . . . . . . . . . . . .  7
     5.2.  Packet Format  . . . . . . . . . . . . . . . . . . . . . .  7
     5.3.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  7
     5.4.  Response to RFC 3942 . . . . . . . . . . . . . . . . . . .  8
     5.5.  Client and Server Behaviour  . . . . . . . . . . . . . . .  8
   6.  Reboot Time Option . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Description  . . . . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Packet Format  . . . . . . . . . . . . . . . . . . . . . .  9
     6.3.  Applicability  . . . . . . . . . . . . . . . . . . . . . . 10
     6.4.  Response to RFC 3942 . . . . . . . . . . . . . . . . . . . 10
     6.5.  Client and Server Behaviour  . . . . . . . . . . . . . . . 10
   7.  Specification Conformance  . . . . . . . . . . . . . . . . . . 11
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     11.2. Informative References . . . . . . . . . . . . . . . . . . 12

Hankins                      Informational                      [Page 2]
RFC 5071                    PXELINUX Options               December 2007

1.  Introduction

   PXE, the Preboot eXecution Environment, is a first-stage network
   bootstrap agent.  PXE is loaded out of firmware on the client host,
   and performs DHCP [3] queries to obtain an IP address.

   Once on the network, it loads a second-stage bootstrap agent as
   configured by DHCP header and option contents.

   PXELINUX is one such second-stage bootstrap agent.  Once PXE has
   passed execution to it, PXELINUX seeks its configuration from a cache
   of DHCP options supplied to the PXE first-stage agent, and then takes
   action based upon those options.

   Most frequently, this implies loading via Trivial File Transfer
   Protocol (TFTP) [6] one or more images that are decompressed into
   memory, then executed to pass execution to the final Host Operating
   System.

   PXELINUX uses DHCP options 208-211 to govern parts of this bootstrap
   process, but these options are not requested by the PXE DHCP client
   at the time it acquires its lease.  At that time, the PXE bootloader
   has no knowledge that PXELINUX is going to be in use, and even so,
   would have no way to know what option(s) PXELINUX might digest.
   Local installations that serve this PXELINUX image to its clients
   must also configure their DHCP servers to provide these options even
   though they are not on the DHCP Parameter Request List [4].

   These options are:

   o  "MAGIC" - 208 - An option whose presence and content verifies to
      the PXELINUX bootloader that the options numbered 209-211 are for
      the purpose as described herein.

   o  "ConfigFile" - 209 - Configures the path/filename component of the
      configuration file's location, which this bootloader should use to