DHC T. Huth
Internet-Draft J. Freimann
Intended status: Standards Track IBM Deutschland Research &
Expires: May 22, 2009 Development GmbH
November 18, 2008
DHCPv6 option for network boot
draft-ietf-dhc-dhcpv6-opt-netboot-02
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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 a new option for DHCPv6 to convey
information, required for network booting, to the nodes.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Netboot option format . . . . . . . . . . . . . . . . . . . . 3
4. Suboptions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Suboption: Boot file Uniform Resource Locator (URL) . . . 4
4.2. Suboption: Vendor class extension . . . . . . . . . . . . 6
5. Appearance of the Netboot option . . . . . . . . . . . . . . . 7
6. Boot protocol considerations . . . . . . . . . . . . . . . . . 8
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 12
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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 download such a file, the
firmware (BIOS) running on the client node must be provided with
information such as: the server on which the boot files can be found,
the protocol to be used for the download (for example TFTP [RFC1350])
and the name of the boot file. Since some kernels or boot loaders
need to be provided with additional parameters, there should also be
the possibility to pass additional parameters along with the server
address, the protocol and the file name.
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 a new DHCPv6 option which is 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].
Terminology specific to IPv6 and DHCPv6 are used in the same way as
defined in the "Terminology" sections of RFC 3315 [RFC3315].
3. Netboot option format
The netboot option is used as an encapsulation for suboptions which
carry the actual information needed to boot a client. This option
will be used by clients to request boot information from a server.
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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_NET_BOOT | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboption-code 1 | suboption-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-data 1 (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. <multiple suboptions> .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboption-code n | suboption-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-data n (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPT_NET_BOOT (TBD1).
option-len Length of the netboot option in octets (not
including the size of the option-code and option-
len fields).
suboption-code, suboption-len and subopt-data together comprise a
suboption for the netboot option. The 16-bit
unsigned suboption-code values are drawn from a
private namespace of the netboot option managed by
IANA (cf. Section 8). The 16-bit unsigned
suboption-len values indicate the length of the
subopt-data field in octets.
Multiple occurences of each suboption-type can occur within a netboot
option (for example when more than one boot server is available).
Clients MUST process the suboptions in the order in which they appear
in the message sent by the server.
So far, only the suboptions in the following chapters have been
defined. Other suboptions might be defined in future RFCs.
4. Suboptions
4.1. Suboption: Boot file Uniform Resource Locator (URL)
This suboption consists of multiple ASCII strings. It is used to
convey an URL to a boot file together with additional parameters for
the boot file (e.g. parameters for the kernel or boot loader
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUBOPT_BOOTFILE_URL | suboption-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| bootfile-len | bootfile-url |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable length) .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| param-len 1 | parameter 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable length) .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. <multiple Parameters> .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| param-len n | parameter n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (variable length) .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
suboption-code SUBOPT_BOOTFILE_URL (1).
suboption-len Length of the bootfile suboption in octets (not
including the size of the suboption-code and
suboption-len fields).
bootfile-len 16-bit integer that specifies the length of the
bootfile-url in octets (not including the bootfile-
length field).
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 (see also the note
below) follows, and then the path, file name and
query parts of the URL. The string is not null-
terminated.
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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 should pass
these parameters in the order they appear in the
SUBOPT_BOOTFILE_URL suboption to the boot file
which has been specified in the bootfile-url field.
In cases where no parameters are needed, everything
but the boot file URL (including its length field)
can be omitted.
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
SUBOPT_BOOTFILE_URL suboption MUST be able to handle IPv6 addresses
here and SHOULD also be able to handle a hostname in the URL. The
IPv6 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.
Since multiple occurrences of SUBOPT_BOOTFILE_URL can be present in a
single OPT_NETBOOT message, clients MUST process them in the order in
which they appear within the message. For example in the case of a
boot file URL the first file should be downloaded and executed. In
case of a failure the process should continue with the second one and
so on.
4.2. Suboption: Vendor class extension
With this suboption, vendors can define their own netboot suboptions:
It can be used by clients and servers to exchange vendor-specific
information which is related to network booting.
This suboption can occur multiple times within a OPT_NET_BOOT option
(also with different enterprise-numbers in case a server and client
implementation supports different vendor extensions). Clients MUST
process them in the order in which they appear within the message.
Unsupported vendor extensions MUST be ignored.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUBOPT_NETBOOT_VENDOR | suboption-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. vendor-class-data .
. (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
suboption-code SUBOPT_NETBOOT_VENDOR (2).
suboption-len Length of the vendor class suboption in octets
(not including the size of the suboption-code and
suboption-len fields).
enterprise-number The enterprise number of the vendor as registered
with IANA (see [VENDORIDS]).
vendor-class-data Vendor-specific information. The meaning is
defined by the vendor identified by the
enterprise-number. It is suggested that the
vendor-class-data SHOULD be composed of a series
of separate items with a two-octets length field
at the beginning of each item, as it is described
for the vendor class option in chapter 22.16 of
[RFC3315].
5. Appearance of the Netboot option
The netboot option MUST NOT appear in DHCPv6 messages other than the
types Solicit, Advertise, Request, Renew, Rebind, Information-Request
and Reply.
The option-code of the netboot option MAY appear in the Option
Request Option in the DHCPv6 message types Solicit, Request, Renew,
Rebind, Information-Request and Reconfigure.
The suboptions MUST appear only in the netboot option.
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6. Boot protocol considerations
RFC 906 [RFC906] suggests to use TFTP for bootstrap loading. Because
it is easy to implement this protocol in firmware (where one has to
deal with size and complexity constraints), this is still the
recommended protocol for network booting. Every firmware
implementation SHOULD at least support this protocol. The boot file
URLs then must be specified according to RFC 3617 [RFC3617].
An alternative approach to TFTP network booting is to bootstrap the
system with iSCSI. In this case, the URL in the SUBOPT_BOOTFILE_URL
suboption 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 SUBOPT_BOOTFILE_URL it is also not necessary
anymore. So for IPv6 iSCSI booting, the "iscsi:" string MUST be
specified as URL in the SUBOPT_BOOTFILE_URL suboption instead.
In some different scenarios, it might also be useful to use other
protocols like FTP or HTTP for network booting, so a firmware
implementation can support these protocols, too. Then it is up to
the network administrator to choose the appropriate boot protocol for
the network, and to specify the right boot file URLs in the DHCPv6
server configuration file.
7. IANA considerations
The following option needs 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_NET_BOOT | TBD1 | Section 3 |
+--------------+-------+--------------+
The OPT_NET_BOOT option also defines a new 16-bit integer suboption
field, for which IANA is to create and maintain a new sub-registry
entitled "Netboot Suboptions" under the OPT_NET_BOOT option. Initial
values for the Netboot Suboptions registry are given below; future
assignments are to be made through IETF Review (see [RFC5226]).
Assignments consist of a suboption name and its associated value.
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+-----------------------+-------+--------------+
| Suboption name | Value | Specified in |
+-----------------------+-------+--------------+
| SUBOPT_BOOTFILE_URL | 1 | Section 4.1 |
| SUBOPT_NETBOOT_VENDOR | 2 | Section 4.2 |
+-----------------------+-------+--------------+
8. Security considerations
The new DHCPv6 option 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 RFC
3315 [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.
9. Acknowledgements
The authors would like to thank Ketan P. Pancholi and Alfred Hoenes
for corrections and suggestions.
Vijayabhaskar Kalusivalingam and Senthil Balasubramanian published a
similar draft for IPv6 network booting some years ago (available at
http://tools.ietf.org/html/draft-ietf-dhc-dhcpv6-opt-rboot-00), which
however was abandoned for unknown reasons.
10. References
10.1. Normative References
[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.,
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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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[VENDORIDS]
IANA, "Private Enterprise Numbers",
<http://www.iana.org/assignments/enterprise-numbers>.
10.2. Informative References
[RFC1350] Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,
RFC 1350, July 1992.
[RFC906] Finlayson, R., "Bootstrap Loading using TFTP", RFC 906,
June 1984.
Authors' Addresses
Thomas H. Huth
IBM Deutschland Research & Development GmbH
Schoenaicher Strasse 220
Boeblingen 71032
Germany
Phone: +49-7031-16-2183
Email: thuth@de.ibm.com
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Jens T. Freimann
IBM Deutschland Research & Development GmbH
Schoenaicher Strasse 220
Boeblingen 71032
Germany
Phone: +49-7031-16-1122
Email: jfrei@de.ibm.com
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