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 (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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