DHC T. Huth
Internet-Draft J. Freimann
Intended status: Standards Track IBM Germany Research &
Expires: October 16, 2009 Development GmbH
V. Zimmer
Intel
D. Thaler
Microsoft
April 14, 2009
DHCPv6 option for network boot
draft-ietf-dhc-dhcpv6-opt-netboot-04
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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 . . . . . . . . . . . . . . . 5
3.3. Client System Architecture Type Option . . . . . . . . . . 6
3.4. Client Network Interface Identifier Option . . . . . . . . 6
4. Appearance of the options . . . . . . . . . . . . . . . . . . 7
5. Download protocol considerations . . . . . . . . . . . . . . . 7
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
Network booting means that a node which should be booted fetches the
files required for booting via its network device from a server.
Network booting is, for example, very useful in environments where
the administrators have to maintain a large number of nodes. Since
all boot and configuration files are stored on a central server, the
maintenance of all nodes can be kept simple this way.
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 are
required for downloading and executing the boot file such as: 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. As
second step, download the boot file from the file server and execute
it.
+------+
_______________________\| DHCP |
/ 1 Get boot file info /|Server|
+------+ +------+
| Host |
+------+ +------+
\_______________________\| File |
2 Download boot file /|Server|
+------+
Figure 1: Network Boot Sequence
DHCPv6 allows client nodes to ask a DHCPv6 server for configuration
parameters. Contrary to its IPv4 predecessor, DHCPv6 does not yet
define a way to query network boot options such as the IPv6 address
of a boot file server and boot file names. Therefore this document
defines new DHCPv6 options which are required for network booting
clients.
2. Conventions
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 [RFC2119].
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Terminology specific to IPv6 and DHCPv6 are used in the same way as
defined in the "Terminology" sections of RFC 3315 [RFC3315].
3. Options
As specified in the DHCPv6 RFC [RFC3315], all values in the options
are in network byte order. Options are byte-aligned but are not
aligned in any other way such as on 2 or 4 byte boundaries. There is
no padding between the options.
3.1. Boot File Uniform Resource Locator (URL) Option
This option consists of an ASCII 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. bootfile-url (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
option-code OPT_BOOTFILE_URL (TBD1).
option-len Length of the bootfile URL option in octets (not
including the size of the option-code and option-
len fields).
bootfile-url This ASCII string is the URL (conforming to
[RFC3986]) for a boot file. This string starts
with the protocol which is used for downloading.
Separated by "://", the hostname or IPv6 address of
the server hosting the boot file follows, and then
the path, file name and query parts of the URL.
The string is not null-terminated.
Note about the bootfile-url: This string can either contain a
hostname or a literal IPv6 address to specify the server where the
boot file should be downloaded from. All clients which implement the
OPT_BOOTFILE_URL option MUST be able to handle IPv6 addresses here
and SHOULD also be able to handle a hostname in the URL. The IPv6
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address in the URL then MUST be enclosed in "[" and "]" characters,
conforming to [RFC3986]. Clients SHOULD also be able to handle
hostnames in the URLs. However, in this case the firmware
implementation on the client machine must support DNS, too. Due to
size limitations, this might not be possible in all firmware
implementations, so support for hostnames in the URLs is only
optional.
Multiple occurrences of OPT_BOOTFILE_URL can be present in a single
DHCP message. Clients MUST process them in the order in which they
appear within the message. The client starts with the first file
that should be downloaded and executed. In case of a failure the
process should continue with the second one and so on.
3.2. Boot File Parameters Option
This option consists of multiple ASCII strings. They are used to
specify parameters for the boot file (e.g. parameters for the kernel
or boot loader program).
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 bootfile parameters option in octets
(not including the size of the option-code and
option-len fields).
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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).
parameters 1...n These ASCII strings are parameters needed for
booting, e.g. kernel parameters. The strings are
not null-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.
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
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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).
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
Depending on the network infrastructure, various special requirements
could be imposed on the download protocol, so this document does not
force one protocol for all scenarios. However, in case there there
are no special requirements, the HTTP protocol SHOULD be used as
download protocol.
RFC 906 [RFC906] suggested to use TFTP for bootstrap loading. Since
TFTP is based on UDP, it has the advantage that it can also be used
in firmware implementations which have to deal with size and
complexity constraints and thus can not include a full-blown TCP/IP
stack. It can also be used in multicast mode (see [RFC2090]) which
is useful when a lot of nodes boot the same boot file at the same
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time. So if TFTP should be used as download protocol, the boot file
URLs then must be specified according to RFC 3617 [RFC3617].
However, TFTP also has some severe limitations, for example
performance limitations due to acknowledging each packet and size
limitations due to using only 16-bit packet counters. So this
specification suggests to use now the well-known and established
hypertext transfer protocol (HTTP, see [RFC2616]) as default for
network booting instead. If a secure download is required, it is
also possible to use HTTP with TLS (HTTPS, see [RFC2818]).
An alternative approach to network booting is to bootstrap the system
with iSCSI. In this case, the URL in the OPT_BOOTFILE_URL option
MUST be specified according to the "iscsi:" string definition in
chapter 5 of [RFC4173]. Note that [RFC4173] also suggests that the
"iscsi:" string should be specified in the so-called "Root Path"
option. However, this option does not exist for DHCPv6 yet, and with
the OPT_BOOTFILE_URL it is also not necessary anymore. So for IPv6
iSCSI booting, the "iscsi:" string MUST be specified as URL in the
OPT_BOOTFILE_URL option instead.
If multiple interfaces are available for booting, it might be a good
strategy to send out requests on each interface in parallel to speed
up the discovery. However how to handle multiple replies, i.e.
replies from more than one DHCP server is not a problem that can be
easily solved on the protocol level. It is up to the implementors to
provide users with a possibility to either choose a network interface
to boot from, or to assign a preference to interfaces or even known
DHCP servers.
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 |
| 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
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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
The new DHCPv6 options described in this document could be sent in
untrusted networks by malicious people with a fake DHCPv6 server to
confuse the booting clients. The clients could 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
SHOULD 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.
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.
The authors would also like to thank Ketan P. Pancholi and Alfred
Hoenes 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
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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.
[RFC3617] Lear, E., "Uniform Resource Identifier (URI) Scheme and
Applicability Statement for the Trivial File Transfer
Protocol (TFTP)", RFC 3617, October 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.
[RFC2090] Emberson, A., "TFTP Multicast Option", RFC 2090,
February 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC906] Finlayson, R., "Bootstrap Loading using TFTP", RFC 906,
June 1984.
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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
Dave Thaler
Microsoft
One Microsoft Way
Redmond WA 98052
USA
Phone: +1 425 703-8835
Email: dthaler@microsoft.com
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