Network Time Protocol Version 4: Protocol and Algorithms Specification
RFC 5905

• Status
• IESG evaluation record
• IESG writeups
• Email expansions
• History

• Versions
• 13

Internet Engineering Task Force (IETF)                          D. Mills
Request for Comments: 5905                                   U. Delaware
Obsoletes: 1305, 4330                                     J. Martin, Ed.
Category: Standards Track                                            ISC
ISSN: 2070-1721                                               J. Burbank
                                                                W. Kasch
                                                                 JHU/APL
                                                               June 2010

 Network Time Protocol Version 4: Protocol and Algorithms Specification

Abstract

   The Network Time Protocol (NTP) is widely used to synchronize
   computer clocks in the Internet.  This document describes NTP version
   4 (NTPv4), which is backwards compatible with NTP version 3 (NTPv3),
   described in RFC 1305, as well as previous versions of the protocol.
   NTPv4 includes a modified protocol header to accommodate the Internet
   Protocol version 6 address family.  NTPv4 includes fundamental
   improvements in the mitigation and discipline algorithms that extend
   the potential accuracy to the tens of microseconds with modern
   workstations and fast LANs.  It includes a dynamic server discovery
   scheme, so that in many cases, specific server configuration is not
   required.  It corrects certain errors in the NTPv3 design and
   implementation and includes an optional extension mechanism.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5905.

Mills, et al.                Standards Track                    [Page 1]
RFC 5905                   NTPv4 Specification                 June 2010

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Notation ......................................5
   2. Modes of Operation ..............................................6
   3. Protocol Modes ..................................................6
      3.1. Dynamic Server Discovery ...................................7
   4. Definitions .....................................................8
   5. Implementation Model ...........................................10
   6. Data Types .....................................................12
   7. Data Structures ................................................16
      7.1. Structure Conventions .....................................16
      7.2. Global Parameters .........................................16
      7.3. Packet Header Variables ...................................17
      7.4. The Kiss-o'-Death Packet ..................................24
      7.5. NTP Extension Field Format ................................25
   8. On-Wire Protocol ...............................................26
   9. Peer Process ...................................................30
      9.1. Peer Process Variables ....................................31
      9.2. Peer Process Operations ...................................33
   10. Clock Filter Algorithm ........................................37