DHC T. Huth
Internet-Draft J. Freimann
Intended status: Standards Track IBM Deutschland Research &
Expires: February 20, 2009 Development GmbH
August 19, 2008
DHCPv6 option for network boot
draft-ietf-dhc-dhcpv6-opt-netboot-00
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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. Suboption: boot file Uniform Resource Locator (URL) . . . . . . 4
5. Appearance of these options . . . . . . . . . . . . . . . . . . 6
6. Boot protocol considerations . . . . . . . . . . . . . . . . . 6
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Security considerations . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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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 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 | subopt-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-data 1 (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. <multiple suboptions> .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboption-code n | subopt-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-data n (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPT_NET_BOOT (tbd).
option-len Length of the netboot option 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 one suboption has been defined, SUBOPT_BOOTFILE_URL,
which is described in Section 4. Other suboptions might be defined
in future RFCs.
4. Suboption: boot file Uniform Resource Locator (URL)
This suboption consists of multiple null-terminated 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 program).
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.
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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_BOOTFILE_URL | subopt-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| bootfile-url |
. (variable) .
| | '\0' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| parameter 1 |
. (variable) .
| | '\0' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. <multiple Parameters> .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| parameter n |
. (variable) .
| | '\0' |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format description:
suboption-code SUBOPT_BOOTFILE_URL (tbd).
suboption-len Length of the bootfile suboption in octets.
bootfile-url This NULL-terminated ASCII string is the URL
(conforming to [RFC2396]) to 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), the path, file name and
query parts of the URL follow.
parameters 1...n These NULL-terminated ASCII strings are parameters
needed for booting, e.g. kernel parameters. In
cases where no parameters are needed, everything
but the boot file URL can be omitted. Parameters
following the boot file name should be directly
related to the boot file (kernel) itself.
Note about the bootfile-url: This string can either contain a
hostname or an IPv6 address to specify the server where the boot file
should be downloaded from. All clients which implement support for
the SUBOPT_BOOTFILE_URL suboption MUST be able to handle IPv6
addresses here. The IPv6 address in the URL then MUST be enclosed in
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"[" and "]" characters, conforming to [RFC2732]. 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.
5. Appearance of these options
The netboot option MUST NOT appear in DHCPv6 messages other than the
types Solicit, Advertise, Request, Renew, Rebind, Information-Request
and Reply.
The number 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 bootfile suboption MUST appear only in the netboot option.
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, so every firmware
implementation SHOULD at least support this protocol. The boot file
URLs then must be specified according to RFC 3617 [RFC3617].
In some cases however, 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
configuration file.
7. 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_NET_BOOT | tbd | Section 3 |
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| SUBOPT_BOOTFILE_URL | tbd | Section 4 |
+---------------------+-------+--------------+
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 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.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2732] Hinden, R., Carpenter, B., and L. Masinter, "Format for
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Literal IPv6 Addresses in URL's", RFC 2732, December 1999.
[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.
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
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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