Timezone Options for DHCP
RFC 4833
Document | Type |
RFC - Proposed Standard
(April 2007; No errata)
Updates RFC 2132
|
|
---|---|---|---|
Authors | Eliot Lear , Paul Eggert | ||
Last updated | 2015-10-14 | ||
Replaces | draft-lear-dhc-timezone-option | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4833 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Jari Arkko | ||
Send notices to | (None) |
Network Working Group E. Lear Request for Comments: 4833 Cisco Systems GmbH Updates: 2132 P. Eggert Category: Standards Track UCLA April 2007 Timezone Options for DHCP Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract Two common ways to communicate timezone information are POSIX 1003.1 timezone strings and timezone database names. This memo specifies DHCP options for each of those methods. The DHCPv4 time offset option is deprecated. Lear & Eggert Standards Track [Page 1] RFC 4833 Timezone Options for DHCP April 2007 1. Introduction This memo specifies a means to provide hosts with more accurate timezone information than was previously available. To do this we make use of two commonly used methods to configure timezones: o POSIX TZ strings o Reference to the name of the time zone entry in the TZ Database POSIX [1] provides a standard for how to express timezone information in a character string. Use of such a string can provide accuracy for at least one transition into and out of daylight saving time (DST), and possibly for more transitions if the transitions are regular enough (e.g., "second Sunday in March at 02:00 local time"). However, for accuracy over longer periods that involve daylight- saving rule changes or other irregular changes, a more detailed mechanism is necessary. The TZ Database [7] that is used in many operating systems provides backwards consistency and accuracy for almost all real-world locations since 1970. The TZ database also attempts to provide a stable set of human readable timezone identifiers. In addition, many systems already make use of the TZ database, and so the names used are a de facto standard. Because the TZ database contains more information, one can heuristically derive the POSIX information from a TZ identifier (see [10] for an example), but the converse is not true. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2]. 1.1. Related Work Dynamic Host Configuration Protocol (DHCP) [3] provides a means for hosts to receive configuration information relating to their current location within an IP version 4 network. [5] similarly does so for IP version 6 networks. RFC 2132 [4] specifies an option to provide client timezone information in the form of an offset in seconds from UTC. The information provided in that option is insufficient for the client to determine whether it is in daylight saving time, and when to change into and out of daylight saving time. In order for the client to properly represent local wall clock time in a consistent and accurate fashion the DHCP server would have to time lease expirations of affected clients to the beginning or end of DST, thus effecting a self stress test (to say the least) at the appointed hour. Lear & Eggert Standards Track [Page 2] RFC 4833 Timezone Options for DHCP April 2007 In addition, an offset is not sufficient to determine the actual timezone in which a client resides, and thus there is no means to derive a human readable abbreviation such as "EST" or "EDT". VTIMEZONE elements are defined in the iCalendar specification [9]. Fully specified they provide a level of accuracy similar to the TZ database. However, because there is currently no global registry of VTIMEZONE TZIDs (although one has been proposed; see [8]), complete accuracy requires that a full entry must be specified. To achieve the same information would range from 300 octets upwards with no particular bound. Furthermore, at the time of this writing the authors are aware of no operating system that natively takes advantage of VTIMEZONE entries. It might be possible to include an option for a TZURL. However, in a cold start environment, it will be bad enough that devices are stressing the DHCP server, and perhaps unwise to similarly afflict other components. 2. New Timezone Options for DHCPv4 The following two options are defined for DHCPv4:Show full document text