Network Working Group                                 A.K. Vijayabhaskar
Internet-Draft                                           Hewlett-Packard
Expires: August 17, November 10, 2002                                     17 Feb                                   10 May 2002

                 Time Configuration Options for DHCPv6
               draft-ietf-dhc-dhcpv6-opt-timeconfig-00.txt
               draft-ietf-dhc-dhcpv6-opt-timeconfig-01.txt

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Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document describes the options for Time related configuration
   information in DHCPv6: NTP Servers and IEEE 1003.1 POSIX Timezone
   specifier.

1. Introduction

   This document describes the options for time related configuration
   information in DHCPv6 [4].

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 [1]

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. IEEE 1003.1 POSIX Timezone option

   The IEEE 1003.1 POSIX Timezone option is used by the server to
   convey client's timezone information to the client.

   The format of the IEEE 1003.1 POSIX 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  IEEE 1003.1 POSIX Timezone
         format [3].

   The format of the IEEE 1003.1 POSIX  timezone  string is specified as
   follows:

      StdOffset[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.

      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.

      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.  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

               Offset has no default value.

      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
               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.

   An Example:

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

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

   In this case,  ``5'' is the Offset  for Std, and ``4'' is the  Offset
   for Dst.  Start is the 116th day at 2am, and End is 298th day at 2am.

6. Appearance of these option

   The NTP servers and IEEE 1003.1 POSIX Timezone options MUST appear
   only in the following messages: Solicit, Advertise, Request,
   Confirm, Renew, Rebind, Information-Request, Reply.

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 IEEE 1003.1 POSIX 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 [4]).

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 [4].

References

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

   [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]  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
        Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
        (DHCPv6)", draft-ietf-dhc-dhcpv6-23 (work in progress), February
        2002.

Author's Addresses

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

   Phone: +91-080-2051424 +91-80-2051424
   E-Mail: vijayak@india.hp.com

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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 Jim Bound and
   Ralph Droms for their thorough review. Thanks to Mike Carney for his
   abstract on Time Zone option.