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Network Working Group                     Vijayabhaskar A Kalusivalingam
Internet-Draft                                           Hewlett-Packard
Expires: May 2004                                               Nov 2003

                  Timezone Specifier Option for DHCPv6

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 May, 2004.

Copyright Notice

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


   This document describes a new DHCPv6 option for passing the client's
   timezone information.

1. Introduction

   This document describes a new option called Timezone option for
   passing the client's timezone information information in DHCPv6 [1].

2. Requirements

   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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3. Terminology

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

4. Timezone option

   The Timezone option is used by the server to convey the timezone
   in which the client resides. The client is expected to set the
   timezone in its system on receiving this option from the server.

   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                          |
      |                              ...                              |

   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 NVT-ASCII string format.
                The format of this string is explained below:


   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 there is no
               Offset followed by the Std, then the timezone is not
               represented in IEEE 1003.1 format. In this case, the
               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:

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                  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.

      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

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

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

      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.


   i) Indian Standard Time zone is represented as:


   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.

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


   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.

      It can also represented as:

    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:


     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.

5. Usage of Timezone option

     The Timezone option has the flexibility of providing timezone
     information in formats other than POSIX timezone, because
     some vendor specific databases can provide more information than
     POSIX Timezone string. The server SHOULD be configurable to send any
     of the format specified in Section 5.

     The timezone option can be used along with the Vendor Class
     Option [1] to make sure that the client and server agree upon the
     meaning of the string. For example, the clients running in different
     OS expect the string in different formats. Here, the Vendor Class
     Option [1] sent by clients can be used by the server to distinguish
     between the clients to return the proper timezone string.

     If the client is not able to interpret the timezone option sent
     by the server, then it SHOULD ignore the option. It MAY contact
     alternative DHCPv6 servers to obtain the timezone information.

6. Appearance of these options

   The Timezone option MUST NOT appear in other than the following the
   following messages:  Solicit, Advertise, Request, 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, Renew, Rebind,
   Information-Request and Reconfigure.

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7. Security Considerations

   The Timezone option may be used by an intruder DHCPv6 server to
   assign invalid time zones, leading to timing issues for the
   applications running on the client machine. For example, because of
   wrongly configured timezone, there is a possibility that some critical
   applications, which are supposed to start at a particular time don't
   get started at that time. A delayed start of OS security update will
   leave the client's machine vulnerable to security attacks.

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

8. 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_TIME_ZONE     tbd      Section 4.

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)", RFC 3315, July 2003.

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

10. Informative References

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

Author's Address

   Vijayabhaskar A Kalusivalingam
   Hewlett-Packard STSD-I
   29, Cunningham Road
   Bangalore - 560052

   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
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   or assist in its implementation may be prepared, copied, published
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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


   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, Margaret Wasserman, Ralph
   Droms, Robert Elz and Thomas Narten 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 Timezone option.

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