Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI
RFC 2030

Document Type RFC - Informational (October 1996; Errata)
Obsoleted by RFC 4330
Obsoletes RFC 1769
Was draft-rfced-info-mills (individual)
Last updated 2013-03-02
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Network Working Group                                           D. Mills
Request for Comments: 2030                        University of Delaware
Obsoletes: 1769                                             October 1996
Category: Informational

             Simple Network Time Protocol (SNTP) Version 4
                         for IPv4, IPv6 and OSI

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   This memorandum describes the Simple Network Time Protocol (SNTP)
   Version 4, which is an adaptation of the Network Time Protocol (NTP)
   used to synchronize computer clocks in the Internet. SNTP can be used
   when the ultimate performance of the full NTP implementation
   described in RFC-1305 is not needed or justified. When operating with
   current and previous NTP and SNTP versions, SNTP Version 4 involves
   no changes to the NTP specification or known implementations, but
   rather a clarification of certain design features of NTP which allow
   operation in a simple, stateless remote-procedure call (RPC) mode
   with accuracy and reliability expectations similar to the UDP/TIME
   protocol described in RFC-868.

   The only significant protocol change in SNTP Version 4 over previous
   versions of NTP and SNTP is a modified header interpretation to
   accommodate Internet Protocol Version 6 (IPv6) [DEE96] and OSI
   [COL94] addressing. However, SNTP Version 4 includes certain optional
   extensions to the basic Version 3 model, including an anycast mode
   and an authentication scheme designed specifically for multicast and
   anycast modes. While the anycast mode extension is described in this
   document, the authentication scheme extension will be described in
   another document to be published later. Until such time that a
   definitive specification is published, these extensions should be
   considered provisional.

   This memorandum obsoletes RFC-1769, which describes SNTP Version 3.
   Its purpose is to correct certain inconsistencies in the previous
   document and to clarify header formats and protocol operations for
   current NTP Version 3 (IPv4) and proposed NTP Version 4 (IPv6 and
   OSI), which are also used for SNTP. A working knowledge of the NTP
   Version 3 specification RFC-1305 is not required for an
   implementation of SNTP.

Mills                        Informational                      [Page 1]
RFC 2030             SNTPv4 for IPv4, IPv6 and OSI          October 1996

1. Introduction

   The Network Time Protocol (NTP) Version 3 specified in RFC-1305
   [MIL92] is widely used to synchronize computer clocks in the global
   Internet. It provides comprehensive mechanisms to access national
   time and frequency dissemination services, organize the time-
   synchronization subnet and adjust the local clock in each
   participating subnet peer. In most places of the Internet of today,
   NTP provides accuracies of 1-50 ms, depending on the characteristics
   of the synchronization source and network paths.

   RFC-1305 specifies the NTP Version 3 protocol machine in terms of
   events, states, transition functions and actions and, in addition,
   engineered algorithms to improve the timekeeping quality and mitigate
   among several synchronization sources, some of which may be faulty.
   To achieve accuracies in the low milliseconds over paths spanning
   major portions of the Internet of today, these intricate algorithms,
   or their functional equivalents, are necessary. However, in many
   cases accuracies in the order of significant fractions of a second
   are acceptable. In such cases, simpler protocols such as the Time
   Protocol [POS83], have been used for this purpose. These protocols
   usually involve an RPC exchange where the client requests the time of
   day and the server returns it in seconds past some known reference

   NTP is designed for use by clients and servers with a wide range of
   capabilities and over a wide range of network delays and jitter
   characteristics. Most users of the Internet NTP synchronization
   subnet of today use a software package including the full suite of
   NTP options and algorithms, which are relatively complex, real-time
   applications (see While the software
   has been ported to a wide variety of hardware platforms ranging from
   personal computers to supercomputers, its sheer size and complexity
   is not appropriate for many applications. Accordingly, it is useful
   to explore alternative access strategies using simpler software
   appropriate for less stringent accuracy expectations.

   This document describes the Simple Network Time Protocol (SNTP)
   Version 4, which is a simplified access strategy for servers and
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