Network Working Group A.K. Vijayabhaskar Internet-Draft Hewlett-Packard Expires:
August 26, 2003 26 FebApril 16, 2004 15 Oct 2003 Time Configuration Options for DHCPv6 draft-ietf-dhc-dhcpv6-opt-timeconfig-02.txtdraft-ietf-dhc-dhcpv6-opt-timeconfig-03.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 26, 2003.April 16, 2004. 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 andSNTP Server addresses - using which the clients can synchronize their system time to that of the standard time servers; Timezone specifier.specifier - used to set the timezone of the clients. 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" section of the DHCPDHCPv6 specification. 4. Simple Network Time Protocol (NTP)(SNTP) Servers option The Simple Network Time Protocol Servers option provides a list of one or more IPIPv6 addresses of NTPSNTP  servers available to the client.client for synchronization. The NTPSNTP servers SHOULD be listed in the order of preference. 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_NTP_SERVERSOPTION_SNTP_SERVERS | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | NTPSNTP server (IP(IPv6 address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | NTPSNTP server (IP(IPv6 address) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code: OPTION_NTP_SERVERSOPTION_SNTP_SERVERS (tbd) option-len: Length of the 'NTP'SNTP server' fields in octets; It must be a multiple of 16 NTPSNTP server: IPIPv6 address of NTPSNTP server 5. Timezone option The Timezone option is used by the server to convey client'sthe timezone informationin which the client resides. The client is expected to set the timezone in its system on receiving this option from the client.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 asof this string is explained below.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 there is no Offset followed by the time-zoneStd, then the timezone is not represented in IEEE 1003.1 POSIX timezone format , thenformat. 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: 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 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. 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. 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  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  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. 7. Appearance of these optionoptions The NTPSNTP servers and Timezone options MUST NOT appear onlyin other than 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  in the following messages: Solicit, Request, Confirm,Renew, Rebind, Information-Request and Reconfigure. 7.8. Security Considerations The NTPSNTP servers option may be used by an intruder DHCPDHCPv6 server to cause DHCPDHCPv6 clients to contact an intruder NTPa 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 applicationapplications running on the client machine less secured.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. The Timezone option may be used by an intruder DHCPDHCPv6 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 DHCPDHCPv6 client SHOULD use authenticated DHCPDHCPv6 (see section"Authentication of DHCP messages" section in the DHCPv6 specification ). 8.9. IANA Considerations IANA is requested to assign an option code to thesethe following options from the option-code space defined in section"DHCPv6 Options" section of the DHCPv6 specification . 9.Option Name Value Described in OPTION_SNTP_SERVERS tbd Section 4. OPTION_TIME_ZONE tbd Section 5. 10. Normative References  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. 10.RFC 3315, July 2003. 11. 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.  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-ISTSD-I 29, Cunningham Road Bangalore - 560052 India Phone: +91-80-2053085 E-Mail: email@example.com 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 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, 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 Time ZoneTimezone option.