Network Working Group                                  V. Kalusivalingam
Internet-Draft                     Cisco Systems (India) Private Limited
Category: Standards Track                                   October 2004


      Simple Network Time Protocol Configuration Option for DHCPv6
                   draft-ietf-dhc-dhcpv6-opt-sntp-01


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Copyright Notice


   Copyright (C) The Internet Society (2004). All Rights Reserved.


Abstract


   This document describes a new DHCPv6 option for passing a list of
   Simple Network Time Protocol (SNTP) server addresses to a client.


. Introduction


   This document describes a new option called SNTP [3] servers Option
   for passing information about SNTP servers in DHCPv6 [1].


. Requirements


   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in RFC 2119 [2].





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. Terminology


   This document uses terminology specific to IPv6 and DHCPv6 as defined
   in "Terminology" section of the DHCPv6 specification [1].


. Simple Network Time Protocol (SNTP) Servers option


   The Simple Network Time Protocol Servers option provides a list of
   one or more IPv6 addresses of SNTP [3] servers available to the
   client for synchronization. The clients use these SNTP servers to
   synchronize their system time to that of the standard time servers.
   Clients MUST treat the list of SNTP servers as an ordered list. The
   server MAY list the SNTP servers in the order of preference.

   The option defined in this document can only be used to configure
   information about SNTP servers that can be reached using IPv6. The
   DHCP option to configure information about IPv4 SNTP servers can be
   found in RFC 2132 [4]. Mechanisms for configuring IPv4/IPv6 dual-
   stack applications are being considered, but are not specified in
   this document.


   The format of the Simple Network Time Protocol Servers option is as
   shown below:


       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_SNTP_SERVERS       |        option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                  SNTP server (IPv6 address)                   |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                  SNTP server (IPv6 address)                   |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   option-code:   OPTION_SNTP_SERVERS (tbd)


   option-len:  Length of the 'SNTP server'  fields in octets; It must be
         a multiple of 16


   SNTP server:    IPv6 address of SNTP server


. Appearance of this option


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



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   messages specified above, the receiver SHOULD ignore the option.

   The option number for this option MAY appear in the Option Request
   Option [1] in the following messages:  Solicit, Request, Renew,
   Rebind, Information-Request and Reconfigure. If this option number appear
   in the Option Request Option in other than the messages specified above,
   the receiver SHOULD ignore the option number.


. Security Considerations


   The SNTP servers option may be used by an intruder DHCPv6 server to
   cause DHCPv6 clients to contact a rogue SNTP server, resulting in
   invalid synchronization of time in client and finally leading to
   time critical applications running inaccurately in client machine.
   The time accuracy can be crucial to some security algorithms. For
   example, it may cause expired certificates to gain a new life, making
   the applications running on the client machine less secure. It can
   even cause clients to set their time incorrectly, making them
   vulnerable to replay attacks in protocols that use time stamps to
   detect replays.


   To avoid attacks through these options, the DHCPv6 client SHOULD use
   authenticated DHCPv6 (see "Authentication of DHCP messages" section
   in the DHCPv6 specification [1]).


. IANA Considerations


   IANA is requested to assign an option code to the following options
   from the option-code space defined in "DHCPv6 Options" section of the
   DHCPv6 specification [1].


   Option Name         Value    Described in
   OPTION_SNTP_SERVERS   tbd     Section 4.


. Normative References


   []  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", RFC 3315, July 2003.


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


. Informative References


   []  D. Mills.  Simple Network Time Protocol (SNTP) Version 4 for
        IPv4, IPv6 and OSI.  Request for Comments (Informational) 2030,
        Internet Engineering Task Force, October 1996.

   []  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
        Extensions", RFC 2132, March 1997.







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Acknowledgements


   Thanks to the DHC Working Group for their time and input into the
   specification. In particular, thanks to (in alphabetical order) Bernie
   Volz, Jim Bound, Margaret Wasserman, Pekka Savola, Ralph Droms, Robert
   Elz and Thomas Narten for their thorough review.


Author's Address


   Vijayabhaskar A Kalusivalingam
   Cisco Systems (India) Private Limited,
   No: 9, Brunton Road,
   Bangalore - 560025
   India

   Phone: +91-80-51036615
   EMail: vibhaska@cisco.com



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Copyright Statement


   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
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Acknowledgment


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