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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 5970

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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   This Internet-Draft will expire on October 16, 2009.

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   Please review these documents carefully, as they describe your rights
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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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