UDP Checksum Complement in the Network Time Protocol (NTP)
RFC 7821

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

• Versions
• 00
• 01
• 02
• 03
• 04
• 05
• 06
• 07

Internet Engineering Task Force (IETF)                        T. Mizrahi
Request for Comments: 7821                                       Marvell
Category: Experimental                                        March 2016
ISSN: 2070-1721

       UDP Checksum Complement in the Network Time Protocol (NTP)

Abstract

   The Network Time Protocol (NTP) allows clients to synchronize to a
   time server using timestamped protocol messages.  To facilitate
   accurate timestamping, some implementations use hardware-based
   timestamping engines that integrate the accurate transmission time
   into every outgoing NTP packet during transmission.  Since these
   packets are transported over UDP, the UDP Checksum field is then
   updated to reflect this modification.  This document proposes an
   extension field that includes a 2-octet Checksum Complement, allowing
   timestamping engines to reflect the checksum modification in the last
   2 octets of the packet rather than in the UDP Checksum field.  The
   behavior defined in this document is interoperable with existing NTP
   implementations.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see 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/rfc7821.

Mizrahi                       Experimental                      [Page 1]
RFC 7821                 NTP Checksum Complement              March 2016

Copyright Notice

   Copyright (c) 2016 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.

Table of Contents

   1. Introduction ....................................................3
      1.1. Intermediate Entities ......................................3
      1.2. Updating the UDP Checksum ..................................4
   2. Conventions Used in This Document ...............................5
      2.1. Terminology ................................................5
      2.2. Abbreviations ..............................................6
   3. Using the UDP Checksum Complement in NTP ........................6
      3.1. Overview ...................................................6
      3.2. Checksum Complement in NTP Packets .........................7
           3.2.1. Using the Checksum Complement .......................7
           3.2.2. Transmission of NTP with Checksum Complement ........8
           3.2.3. Updates of NTP with Checksum Complement .............8
           3.2.4. Reception of NTP with Checksum Complement ...........8
      3.3. Interoperability with Existing Implementations .............9
      3.4. The Checksum Complement and Authentication .................9
   4. Security Considerations ........................................10
   5. IANA Considerations ............................................10
   6. References .....................................................11
      6.1. Normative References ......................................11
      6.2. Informative References ....................................11
   Appendix A. Checksum Complement Usage Example .....................13
   Acknowledgments ...................................................14
   Author's Address ..................................................14

Mizrahi                       Experimental                      [Page 2]
RFC 7821                 NTP Checksum Complement              March 2016

1.  Introduction

   The Network Time Protocol [NTPv4] allows clients to synchronize their
   clocks to a time server by exchanging NTP packets.  The increasing
   demand for highly accurate clock synchronization motivates
   implementations that provide accurate timestamping.

1.1.  Intermediate Entities

   In this document, we use the term "intermediate entity" to refer to