DHC T. Huth
Internet-Draft J. Freimann
Intended status: Standards Track IBM Germany Research &
Expires: April 29, 2010 Development GmbH
V. Zimmer
Intel
D. Thaler
Microsoft
October 26, 2009
DHCPv6 option for network boot
draft-ietf-dhc-dhcpv6-opt-netboot-06
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Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) provides a
framework for passing configuration information to nodes on a
network. This document describes new options for DHCPv6 which are
required for booting a node from the network.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Boot File Uniform Resource Locator (URL) Option . . . . . 4
3.2. Boot File Parameters Option . . . . . . . . . . . . . . . 4
3.3. Client System Architecture Type Option . . . . . . . . . . 5
3.4. Client Network Interface Identifier Option . . . . . . . . 6
4. Appearance of the options . . . . . . . . . . . . . . . . . . 7
5. Download protocol considerations . . . . . . . . . . . . . . . 7
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
This draft describes DHCPv6 options that can be used to provide
configuration information for a node that must be booted using the
network, rather than from local storage.
Network booting is used, for example, in some environments where
administrators have to maintain a large number of nodes. By serving
all boot and configuration files from central server, the effort
required to maintain these nodes is greatly reduced.
A typical boot file would be, for example, an operating system kernel
or a boot loader program. To be able to execute such a file, the
firmware (BIOS) running on the client node must perform the following
two steps (see Figure 1): First get all information which is required
for downloading and executing the boot file. Second, download the
boot file and execute it.
+------+
_______________________\| DHCP |
/ 1 Get boot file info /|Server|
+------+ +------+
| Host |
+------+ +------+
\_______________________\| File |
2 Download boot file /|Server|
+------+
Figure 1: Network Boot Sequence
Information that is required for booting over the network can include
information about the server on which the boot files can be found,
the protocol to be used for the download (for example HTTP [RFC2616]
or TFTP [RFC1350]), the name of the boot file and additional
parameters which should be passed to the OS kernel or boot loader
program respectively.
DHCPv6 allows client nodes to ask a DHCPv6 server for configuration
parameters. This document provides new options which a client can
request from the DHCPv6 server to satisfy its requirements for
booting.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in RFC 2119 [RFC2119].
Terminology specific to IPv6 and DHCPv6 are used in the same way as
defined in the "Terminology" sections of RFC 3315 [RFC3315].
3. Options
Option formats comply with DHCPv6 options per [RFC3315] (section 6).
3.1. Boot File Uniform Resource Locator (URL) Option
This option consists of an UTF-8 string. It is used to convey an URL
to a boot file.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPT_BOOTFILE_URL | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. boot-file-url (variable length) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
option-code OPT_BOOTFILE_URL (TBD1).
option-len Length of the Boot File URL option in octets (not
including the size of the option-code and option-
len fields).
boot-file-url This UTF-8 string is the URL for the boot file, as
defined in [RFC3986]. The string is not NUL-
terminated.
If the URL is expressed using an IPv6 address rather than a domain
name, the address in the URL then MUST be enclosed in "[" and "]"
characters, conforming to [RFC3986]. Clients that have DNS
implementations should support the use of domain names in the URL.
3.2. Boot File Parameters Option
This option consists of multiple UTF-8 strings. They are used to
specify parameters for the boot file (similar to the command line
arguments in most modern operating systems). For example, these
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parameters could be used to specify the root file system of the OS
kernel, or where a second stage boot loader can download its
configuration file from.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPT_BOOTFILE_PARAM | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| param-len 1 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ parameter 1 .
. (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. <multiple Parameters> .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| param-len n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ parameter n .
. (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
option-code OPT_BOOTFILE_PARAM (TBD2).
option-len Length of the Boot File Parameters option in octets
(not including the size of the option-code and
option-len fields).
param-len 1...n This is a 16-bit integer which specifies the length
of the following parameter in octets (not including
the parameter-length field).
parameter 1...n These UTF-8 strings are parameters needed for
booting, e.g. kernel parameters. The strings are
not NUL-terminated.
The firmware MUST pass these parameters in the order they appear in
the OPT_BOOTFILE_PARAM option to the boot file which has been
specified in the OPT_BOOTFILE_URL option.
3.3. Client System Architecture Type Option
This option provides parity with the Client System Architecture Type
Option defined for DHCPv4 in [RFC4578] section 2.1.
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The format of the option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_ARCH_TYPE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Architecture Type (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CLIENT_ARCH_TYPE (TBD3).
option-len Length of the "processor architecture type" field
in octets (not including the option-code and
option-len fields). It MUST be an even number
greater than zero. See [RFC4578] section 2.1 for
details.
Architecture Type A list of one or more architecture types, as
specified in [RFC4578] section 2.1.
3.4. Client Network Interface Identifier Option
The Client Network Interface Identifier option is sent by a DHCP
client to a DHCP server to provide information about its level of
Universal Network Device Interface (UNDI) support (see also [PXE21]
and [UEFI22]).
This option provides parity with the Client Network Interface
Identifier Option defined for DHCPv4 in [RFC4578] section 2.2.
The format of the option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_NII | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Major | Minor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_NII (TBD4).
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option-len 3
Type As specified in [RFC4578] section 2.2.
Major As specified in [RFC4578] section 2.2.
Minor As specified in [RFC4578] section 2.2.
4. Appearance of the options
These options MUST NOT appear in DHCPv6 messages other than the types
Solicit, Advertise, Request, Renew, Rebind, Information-Request and
Reply.
The option-codes of these options MAY appear in the Option Request
Option in the DHCPv6 message types Solicit, Request, Renew, Rebind,
Information-Request and Reconfigure.
5. Download protocol considerations
The Boot File URL option does not place any constraints on the
protocol used for downloading the boot file, other than that it must
be possible to specify it in a URL. For the sake of administrative
simplicity, we strongly recommend that, at a mininum, implementors of
network boot loaders implement the well-known and established
hypertext transfer protocol (HTTP, see [RFC2616]) for downloading.
Please note that for IPv6, this supersedes [RFC906] which recommended
to use TFTP for downloading (see [RFC3617] for TFTP URL definition).
When using iSCSI for booting, the "iscsi:"-URI is formed as defined
in [RFC4173]. The functionality attributed in RFC4173 to a root path
option is provided for IPv6 by the Boot File URL option instead.
6. IANA considerations
The following options need to be assigned by the IANA from the option
number space defined in the chapter 22 of the DHCPv6 RFC [RFC3315].
+-------------------------+-------+--------------+
| Option name | Value | Specified in |
+-------------------------+-------+--------------+
| OPT_BOOTFILE_URL | TBD1 | Section 3.1 |
| OPT_BOOTFILE_PARAM | TBD2 | Section 3.2 |
| OPTION_CLIENT_ARCH_TYPE | TBD3 | Section 3.3 |
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| OPTION_NII | TBD4 | Section 3.4 |
+-------------------------+-------+--------------+
This document also introduces a new IANA registry for processor
architecture types. The name of this registry shall be "Processor
Architecture Type". Registry entries consist of a 16-bit integer
recorded in decimal format, and a descriptive name. The initial
values of this registry can be found in [RFC4578] section 2.1.
The assignment policy for values shall be Expert Review (see
[RFC5226]), and any requests for values must supply the descriptive
name for the processor architecture type.
7. Security considerations
In untrusted networks, a rogue DHCPv6 server could send the new
DHCPv6 options described in this document. The booting clients could
then be provided with a wrong URL so that the boot either fails, or
even worse, the client boots the wrong operating system which has
been provided by a malicious file server. To prevent this kind of
attack, clients can use authentication of DHCPv6 messages (see
chapter 21. in [RFC3315]).
Note also that DHCPv6 messages are sent unencrypted by default. So
the boot file URL options are sent unencrypted over the network, too.
This can become a security risk since the URLs can contain sensitive
information like user names and passwords (for example a URL like
"ftp://username:password@servername/path/file"). At the current
point in time, there is no possibility to send encrypted DHCPv6
messages, so it is strongly recommended not to use sensitive
information in the URLs in untrusted networks.
Even if the DHCPv6 transaction is secured, this does not protect
against attacks on the boot file download channel. Consequently, we
recommend that either a protocol like HTTPS (see [RFC2817] and
[RFC2818]) be used to prevent spoofing, or that the boot loader
implementation implement a mechanism for signing boot images and a
configurable signing key in memory, so that if a malicious image is
provided, it can be detected and rejected.
8. Acknowledgements
The authors would like to thank Ruth Li, Dong Wei, Kathryn Hampton,
Phil Dorah, Richard Chan, and Fiona Jensen for discussions that led
to this document.
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The authors would also like to thank Ketan P. Pancholi, Alfred
Hoenes, Gabriel Montenegro and Ted Lemon for corrections and
suggestions.
9. References
9.1. Normative References
[PXE21] Johnston, M., "Preboot Execution Environment (PXE)
Specification", September 1999,
<http://www.pix.net/software/pxeboot/archive/pxespec.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4173] Sarkar, P., Missimer, D., and C. Sapuntzakis,
"Bootstrapping Clients using the Internet Small Computer
System Interface (iSCSI) Protocol", RFC 4173,
September 2005.
[RFC4578] Johnston, M. and S. Venaas, "Dynamic Host Configuration
Protocol (DHCP) Options for the Intel Preboot eXecution
Environment (PXE)", RFC 4578, November 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[UEFI22] UEFI Forum, "Unified Extensible Firmware Interface
Specification, Version 2.2", September 2008,
<http://www.uefi.org/>.
9.2. Informative References
[RFC1350] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
RFC 1350, July 1992.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
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Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3617] Lear, E., "Uniform Resource Identifier (URI) Scheme and
Applicability Statement for the Trivial File Transfer
Protocol (TFTP)", RFC 3617, October 2003.
[RFC906] Finlayson, R., "Bootstrap Loading using TFTP", RFC 906,
June 1984.
Authors' Addresses
Thomas H. Huth
IBM Germany Research & Development GmbH
Schoenaicher Strasse 220
Boeblingen 71032
Germany
Phone: +49-7031-16-2183
Email: thuth@de.ibm.com
Jens T. Freimann
IBM Germany Research & Development GmbH
Schoenaicher Strasse 220
Boeblingen 71032
Germany
Phone: +49-7031-16-1122
Email: jfrei@de.ibm.com
Vincent Zimmer
Intel
2800 Center Drive
DuPont WA 98327
USA
Phone: +1 253 371 5667
Email: vincent.zimmer@intel.com
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Dave Thaler
Microsoft
One Microsoft Way
Redmond WA 98052
USA
Phone: +1 425 703-8835
Email: dthaler@microsoft.com
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