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Network Working Group                                 A.K. Vijayabhaskar
Internet-Draft                                           Hewlett-Packard
Expires: August 26, 2003                                     26 Feb 2003


                 Time Configuration Options for DHCPv6
               draft-ietf-dhc-dhcpv6-opt-timeconfig-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on August 26, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes the options for Time related configuration
   information in DHCPv6: NTP Servers and Timezone specifier.

1. Introduction

   This document describes the options for time related configuration
   information in DHCPv6 [1].

2. 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 [4]






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3. Terminology

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

4. Network Time Protocol (NTP) Servers option

   The Network Time Protocol Servers option provides a list of one or
   more IP addresses of NTP [2] servers available to the client. The
   NTP servers SHOULD be listed in the order of preference.

   The format of the 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_NTP_SERVERS       |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   NTP server (IP address)                     |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   NTP server (IP address)                     |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   option-code:   OPTION_NTP_SERVERS (tbd)

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

   NTP server:    IP address of NTP server

5. Timezone option

   The Timezone option is used by the server to convey client's timezone
   information to the client.

   The format of the Timezone 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_TIME_ZONE       |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            time-zone                          |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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   option-code:   OPTION_TIME_ZONE (tbd)

   option-len: Length of the 'time-zone' field in octets

   time-zone:   Time zone of the client in the format as explained below.

      Std[Offset[Dst[Offset],[Start[/Time],End[/Time]]]]

   where '[' and ']' enclose optional fields, '|' indicates choice
   of exactly one of the alternatives, ',' and '/' represent literal
   characters present in the string.

   If "Offset" is specified, then the time-zone is represented in the
   IEEE 1003.1 POSIX timezone format [3].

      Std      Three or more octets for the standard timezone (Std).
               Any character (or case) except a leading colon, digits,
               comma, minus or plus sign is allowed. If the time-zone
               is not represented in IEEE 1003.1 POSIX timezone format [3],
               then Std is treated as the index to the timezone database,
               for example, a file name, from where additional information
               about the timezone may be obtained.

      Offset   Indicates the value one must add to local time to
               arrive at UTC, of the form:  [+|-]hh[:mm[:ss]].  Offset
               following Std is required, if the timezone is represented
               in IEEE 1003.1 POSIX timezone format. Digits are always
               interpreted as decimal number.  If preceded by a '-', the
               timezone is east of the Prime Meridian, otherwise it is west
               ('+' is optional) The permissible values for hh[:mm[:ss]] are
               as follows:

                  hh       0 <= hh <= 23

                  mm       0 <= mm <= 60

                  ss       0 <= ss <= 60

      Dst      Three or more octets for the daylight savings timezone.
               If Dst is missing, then daylight savings time does not
               apply in this locale.  If no Offset follows Dst, then
               Dst is assumed to be one hour ahead of standard time.
               Any character (or case) except a leading colon, digits,
               comma, minus or plus sign is allowed.

      Start    Indicates the day of the year, in one of the formats
               indicated below, when to change to daylight savings time.
               The ``Time'' field (which follows immediately after a
               ``/'' character, if present) indicates when the change is
               made, in local time.






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      End      Indicates the day of the year, in one of the formats
               indicated below, when to change back from daylight
               savings time.  The ``Time'' field (which follows
               immediately after a ``/'' character, if present)
               indicates when the change is made, in local time.

      Time     Time has the same format as Offset, except that no
               leading ``-'' or ``+'' is permitted.  The default is
               02:00:00.

   The day of the year needs to be given in any of the following
   formats:

      Jn       The julian day n, (1 <= n <= 365).  Leap days are not
               counted.

      n        Zero-based julian day, (0 <= n <= 365).  Leap days are
               counted so it is possible to refer to Feb 29.

      Mm.n.d   The ``d''th day, (0 <= d <= 6) of week ``n'' of month
               ``m'' of the year (1 <= n <= 5, 1 <= m <= 12, where week
               5 means last ``d'' day in month ``m'' which may occur in
               either the fourth or the fifth week.  Week ``1'' is the
               first week in which the ``d'' day occurs. Day ``0'' refers
               Sunday, day ``1'' refers Monday and so on.

   Examples:

   i) Indian Standard Time zone is represented as:

      IST-5:30

   Here, ``IST'' refers the standard timezone and ``-5:30'' is the offset.
   `-' sign in the offset says that the timezone is 5 hours and 30 minutes
   ahead of UTC. Absence of ``Dst'' says that daylight savings doesn't apply
   to this locale.

   ii) For Eastern USA time zone, 1986, the timezone string is as shown below:

      EST5EDT4,116/02:00:00,298/02:00:00

   It says:

   The standard time zone is in 5 hours behind UTC. The Daylight Savings
   Timezone is 4 hours behind UTC. Day light savings starts at 116 day, i.e.,
   April 27 02:00 AM standard time and ends at 298th day, i.e., October 26
   02:00 AM daylight time.








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      It can also represented as:

      EST5EDT,116/02:00:00,298/02:00:00

    Since no offset follows the ``Dst'', daylight savings time is 1 hour
    ahead of standard time, thus, it is 4 hours behind UTC.

    iii) Representing ii) in the non POSIX standard way is:

       America/New-York

     It says that the locale belongs to New-York timezone in America, which
     will be used as the index in to a timezone database to get more
     information of the timezone.

6. Appearance of these option

   The NTP servers and Timezone options MUST appear only in the following
   messages: Solicit, Advertise, Request, Confirm, Renew, Rebind,
   Information-Request and Reply.

   The option number for these options MAY appear in the Option Request
   Option [1] in the following messages: Solicit, Request, Confirm, Renew,
   Rebind, Information-Request and Reconfigure.

7. Security Considerations

   The NTP servers option may be used by an intruder DHCP server to
   cause DHCP clients to contact an intruder NTP 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 application less secured.

   The Timezone option may be used by an intruder DHCP server to assign
   invalid time zones, leading to timing issues for the applications running
   on the client machine.

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

8. IANA Considerations

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

9. Normative References

   [1]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November
        2002.


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10. Informative References

   [2]  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.

   [3]  IEEE, "1003.1 POSIX Timezone Specification", 1988.

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

Author's Addresses

   Vijayabhaskar A K
   Hewlett-Packard ESD-I
   29, Cunningham Road
   Bangalore - 560052
   India

   Phone: +91-80-2053085
   E-Mail: vijayak@india.hp.com



































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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
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   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society. 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, Ralph Droms, Robert Elz for their thorough
   review. Special thanks to Robert Elz for his suggestions and help in
   making this document more readable. Thanks to Mike Carney for his abstract
   on Time Zone option.





















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