Network Working Group A.K. Vijayabhaskar Internet-Draft Hewlett-Packard Expires:
November 10, 2002 10 May 2002August 26, 2003 26 Feb 2003 Time Configuration Options for DHCPv6 draft-ietf-dhc-dhcpv6-opt-timeconfig-01.txtdraft-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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 17, 2002.26, 2003. Copyright Notice Copyright (C) The Internet Society (2002).(2003). All Rights Reserved. Abstract This document describes the options for Time related configuration information in DHCPv6: NTP Servers and IEEE 1003.1 POSIXTimezone specifier. 1. Introduction This document describes the options for time related configuration information in DHCPv6 .. 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  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  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 POSIXTimezone option The IEEE 1003.1 POSIXTimezone option is used by the server to convey client's timezone information to the client. The format of the IEEE 1003.1 POSIXTimezone 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 . The format ofthe IEEE 1003.1 POSIX timezone string is specifiedformat as follows: StdOffset[Dst[Offset],[Start[/Time],End[/Time]]]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 . 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 , 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.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 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: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 Posixtimezone 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''It says: The standard time zone is the Offset for Dst. Startin 5 hours behind UTC. The Daylight Savings Timezone is the 116th day4 hours behind UTC. Day light savings starts at 2am,116 day, i.e., April 27 02:00 AM standard time and End is 298th dayends at 2am.298th day, i.e., October 26 02:00 AM daylight time. 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 IEEE 1003.1 POSIXTimezone options MUST appear only in the following messages: Solicit, Advertise, Request, Confirm, Renew, Rebind, Information-Request,Information-Request and Reply. The option number for these options MAY appear in the Option Request Option  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 IEEE 1003.1 POSIXtime 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 ).). 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 .. 9. Normative References  Bradner, S., "Key wordsBound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. Droms (ed.), "Dynamic Host Configuration Protocol for useIPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.progress), November 2002. 10. 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.  IEEE, "1003.1 POSIX Timezone Specification", 1988.  Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. Droms (ed.), "Dynamic Host Configuration ProtocolBradner, S., "Key words for IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-23 (workuse in progress), February 2002.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: +91-80-2051424+91-80-2053085 E-Mail: firstname.lastname@example.org Full Copyright Statement Copyright (C) The Internet Society (2002).(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 or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 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 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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 andBound, Ralph DromsDroms, 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.