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Versions: 00 01 02 03 04 05 06 RFC 5908

Network Working Group                                         R. Gayraud
Internet-Draft                                              B. Lourdelet
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: January 12, 2009                                  July 11, 2008


          Network Time Protocol (NTP) Server Option for DHCPv6
                  draft-ietf-ntp-dhcpv6-ntp-opt-02.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on January 12, 2009.

Abstract

   The NTP Server Option for DHCPv6 provides NTP (Network Time Protocol
   version 4) configuration information to DHCPv6 hosts.













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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Related Work and Usage Model . . . . . . . . . . . . . . .  3
   3.  NTP Server Option for DHCPv6 . . . . . . . . . . . . . . . . .  4
     3.1.  NTP Server Address Suboption . . . . . . . . . . . . . . .  5
     3.2.  NTP Multicast Address Suboption  . . . . . . . . . . . . .  6
     3.3.  NTP Server FQDN Suboption  . . . . . . . . . . . . . . . .  6
   4.  Examples of use  . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Appearance of this Option  . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 11

































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1.  Requirements notation

   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 [RFC2119].


2.  Introduction

   This document defines a DHCPv6 option and associated suboptions to
   provide Network Time Protocol version 4 [draft-ntpv4] or greater
   configuration information to DHCPv6 hosts.

2.1.  Related Work and Usage Model

   [RFC4075] (SNTP Configuration Option for DHCPv6) provides some degree
   of automatic time server configuration for IPv6, as it specifies how
   to transmit SNTP [RFC4330] servers addresses through DHCPv6.
   However, this approach is not suitable for all NTP deployments.  The
   use of the SNTP protocol is only authorized at the root and leafs of
   an NTP tree (i.e. stratum 1 servers and highest stratum clients).
   But NTP servers that receive time from an upstream source, and
   redistribute it to LAN workstations, are not allowed to run SNTP.
   This is why SNTP is not the protocol of choice for general purpose
   NTP servers directly used by client workstations.  Additionally the
   approach of only offering IPv6 addresses to specify server location
   does not meet NTP requirements that make uses of a FQDN (Fully
   Qualified Domain Name) as well.

   The NTP service is publicly offered on the Internet by a number of
   organizations.  Those servers can be used but not abused, so any
   method which is tasked to disseminate locations of NTP servers must
   act responsibly in a manner that does not lead to public server
   overloading.  When using DHCPv6 to offer NTP server location, and if
   there is a need to distribute a device with a hardcoded
   configuration, this configuration MUST NOT include server location
   that is not part of the organization that distribute this device.
   Typical usage of this option is to specify an NTP server that is part
   of the organization that operates the DHCPv6 server.

   The location of the NTP service, like any other Internet service, can
   be specified by an IP address or an FQDN.  By design, DHCP offers
   information to multiple devices and is prone to amplification of
   mistakes, so great care must be taken to define its configuration.
   Specification of the NTP service by FQDN offers a level of
   indirection that works as a possible mitigation tool in case of
   misconfiguration.  DNS can be used to redirect misconfigured clients
   to an unexisting IPv6 address instead of having to change the address



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   of the NTP Server itself.

   While the NTP specification defines a comprehensive set of
   configuration parameters, modification of those parameters is best
   left to the decision of the client itself.  The DHCPv6 option for NTP
   is then restricted to server location.


3.  NTP Server Option for DHCPv6

   This option serves as a container for all the information related to
   one NTP server.  This option can appear multiple times in a DHCPv6
   message.  Each instance of this option is to be considered by the NTP
   client as a server to include in its configuration.

   The option itself does not contain any value.  Instead, it contains
   one or several suboptions that carry NTP server configuration
   information.  This option MUST include one, and only one, time source
   suboption.  The currently defined time source suboptions are:
   NTP_OPTION_SRV_ADDR, NTP_OPTION_SRV_MC_ADDR, NTP_OPTION_SRV_FQDN.  It
   carries the NTP server location, as a unicast or multicast IPv6
   address or as an NTP server FQDN.  More time source suboptions may be
   defined in the future.  While the FQDN option offers the most
   deployment flexibility, resiliency as well as security, the IP
   address options are defined to cover cases where a dependancy to DNS
   is not desirable.

   If the NTP server location is an IPv6 multicast address, the client
   SHOULD use this address as an NTP multicast group address and listen
   to messages sent to this group in order to synchronize its clock.





















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   The format of the NTP Server 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_NTP_SERVER        |          option-len           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         suboption-1                           |
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         suboption-2                           |
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         suboption-n                           |
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       option-code: OPTION_NTP_SERVER (TBD_IANA),

       option-len: Total length of the included suboptions.

   A client that receives this option SHOULD use the specified NTP
   server to synchronize its clock.

   This document does not define any priority between the client's
   embedded configuration and the NTP servers discovered via this
   option.  In particular, the client is allowed to simultaneously use
   its own configured NTP servers and the servers discovered via DHCP.

3.1.  NTP Server Address Suboption

   This suboption is intended to appear inside the OPTION_NTP_SERVER
   option.  It specifies the IPv6 unicast address of an NTP server
   available to the client.  An example of use is present in Section 4.















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   The format of the NTP Server Address Suboption 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_SRV_ADDR     |        suboption-len = 16     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                                                               |
     |                   IPv6 address of NTP server                  |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       suboption-code: NTP_SUBOPTION_SRV_ADDR (1),

       suboption-len: 16.

3.2.  NTP Multicast Address Suboption

   This suboption is intended to appear inside the OPTION_NTP_SERVER
   option.  It specifies the IPv6 address of the IPv6 multicast group
   address used by NTP on the local network.  An example of use is
   present in Section 4.

   The format of the NTP Multicast Address Suboption 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_MC_ADDR      |        suboption-len = 16     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                                                               |
     |                   Multicast IPv6 address                      |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       suboption-code: NTP_SUBOPTION_MC_ADDR (2),

       suboption-len: 16.

3.3.  NTP Server FQDN Suboption

   This suboption is intended to appear inside the OPTION_NTP_SERVER
   option.  It specifies the FQDN of an NTP server available to the
   client.





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   The format of the NTP Server FQDN Suboption 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_SRV_FQDN     |         suboption-len         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                      FQDN of NTP server                       |
     :                                                               :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       suboption-code: NTP_SUBOPTION_SRV_FQDN (3),

       suboption-len: Length of the included FQDN field,

       FQDN: Fully Qualidied Domain Name of the NTP server. This
             field MUST be encoded as described in [RFC3315],
             section 8.


4.  Examples of use

   To instruct a client to use an NTP server located at address 2001:
   db8::1, a DHCP server shall use the following format:

      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_NTP_SERVER        |        option-len = 20        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_SRV_ADDR     |        suboption-len = 16     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                 IPv6 address  =  2001:db8::1                  |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+













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   To to enable a client to use the 'ntp.example.com' server, a DHCP
   server shall use the following format:

      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_NTP_SERVER        |        option-len = 21        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_SRV_FQDN     |        suboption-len = 17     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       3       |      'n'      |      't'      |      'p'      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       7       |      'e'      |      'x'      |      'a'      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      'm'      |      'p'      |      'l'      |      'e'      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       3       |      'c'      |      'o'      |      'm'      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       0       |
     +-+-+-+-+-+-+-+-+

   To instruct a client to join the FF05::101 NTP multicast group, a
   DHCP server shall use the following format:

      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_NTP_SERVER        |        option-len = 20        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    NTP_SUBOPTION_MC_ADDR      |        suboption-len = 16     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                   IPv6 address  =  FF05::101                  |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.  Appearance of this Option

   The OPTION_NTP_SERVER option can appear multiple times in a DHCPv6
   message.  The order in which these options appear is not significant.
   The client uses its usual algorithms to determine which server(s) or
   multicast group(s) should be prefered to synchronize its clock.

   The OPTION_NTP_SERVER option MUST NOT appear in messages other than
   the following: Solicit, Advertise, Request, Renew, Rebind,
   Information-Request, and Reply.  If this option appears in messages



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   other than those specified above, the receiver SHOULD ignore it.

   The option number for this option MAY appear in the "Option Request"
   option [RFC3315] in the following messages: Solicit, Request, Renew,
   Rebind, Information-Request, and Reconfigure.  If this option number
   appears in the "Option Request" option in messages other than those
   specified above, the receiver SHOULD ignore it.


6.  Security Considerations

   This option could be used by an intruder to advertise the address of
   a malicious NTP server and adversely affect the clock of clients on
   the network.  The consequences of such an attack can be critical,
   because many security protocols depend on time synchronization to run
   their algorithms.  As an example, an attacker could break
   connectivity between SEND-enabled nodes [RFC3971], simply by
   affecting the clock on these nodes.

   To prevent these attacks, it is strongly advisable to secure the use
   of this option either by:

      -  using the NTPv4 Autokey public key authentication, as defined
         in [draft-autokey] or,

      -  using authenticated DHCP as described in [RFC3315] section 21.


7.  IANA Considerations

   When this document is published, the IANA is requested to assign an
   option code from the "DHCPv6 Options Codes" registry for
   OPTION_NTP_SERVER.


8.  References

8.1.  Normative References

   [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.

   [draft-ntpv4]
              Burbank, J., Kasch, W., Martin, J., and D. Mills, "Network
              Time Protocol Version 4 Protocol And Algorithms
              Specification", draft-ietf-ntp-ntpv4-proto-08 (work in
              progress), November 2007.



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   [draft-autokey]
              Haberman, B. and D. Mills, "Network Time Protocol Version
              4 Autokey Specification", draft-ietf-ntp-autokey-00 (work
              in progress), September 2007.

8.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC4075]  Kalusivalingam, V., "Simple Network Time Protocol (SNTP)
              Configuration Option for DHCPv6", RFC 4075, May 2005.

   [RFC4330]  Mills, D., "Simple Network Time Protocol (SNTP) Version 4
              for IPv4, IPv6 and OSI", RFC 4330, January 2006.


Authors' Addresses

   Richard Gayraud
   Cisco Systems, Inc.
   Village ent. GreenSide, Bat T3,
   400, Av de Roumanille,
   06410 BIOT - Sophia-Antipolis Cedex
   France

   Phone: +33 4 97 23 26 49
   Email: rgayraud@cisco.com


   Benoit Lourdelet
   Cisco Systems, Inc.
   Village ent. GreenSide, Bat T3,
   400, Av de Roumanille,
   06410 BIOT - Sophia-Antipolis Cedex
   France

   Phone: +33 4 97 23 26 23
   Email: blourdel@cisco.com









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Full Copyright Statement

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   contained in BCP 78, and except as set forth therein, the authors
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