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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 Deutschland Research &
Expires: May 22, 2009                                   Development GmbH
                                                       November 18, 2008


                     DHCPv6 option for network boot
                  draft-ietf-dhc-dhcpv6-opt-netboot-02

Status of this Memo

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   This Internet-Draft will expire on May 22, 2009.

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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Full Copyright Statement

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