Network Time Protocol Best Current Practices
RFC 8633

Document Type RFC - Best Current Practice (July 2019; No errata)
Also known as BCP 223
Last updated 2019-07-18
Replaces draft-reilly-ntp-bcp
Stream IETF
Formats plain text html pdf htmlized bibtex
Reviews
Stream WG state Submitted to IESG for Publication
Document shepherd Karen O'Donoghue
Shepherd write-up Show (last changed 2018-12-13)
IESG IESG state RFC 8633 (Best Current Practice)
Consensus Boilerplate Yes
Telechat date
Responsible AD Suresh Krishnan
Send notices to Karen O'Donoghue <odonoghue@isoc.org>
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
Internet Engineering Task Force (IETF)                    D. Reilly, Ed.
Request for Comments: 8633                                    Orolia USA
BCP: 223                                                        H. Stenn
Category: Best Current Practice                  Network Time Foundation
ISSN: 2070-1721                                                D. Sibold
                                                                     PTB
                                                               July 2019

              Network Time Protocol Best Current Practices

Abstract

   The Network Time Protocol (NTP) is one of the oldest protocols on the
   Internet and has been widely used since its initial publication.
   This document is a collection of best practices for the general
   operation of NTP servers and clients on the Internet.  It includes
   recommendations for the stable, accurate, and secure operation of NTP
   infrastructure.  This document is targeted at NTP version 4 as
   described in RFC 5905.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   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
   BCPs is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8633.

Reilly, et al.            Best Current Practice                 [Page 1]
RFC 8633                Network Time Protocol BCP              July 2019

Copyright Notice

   Copyright (c) 2019 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
   (https://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.

Reilly, et al.            Best Current Practice                 [Page 2]
RFC 8633                Network Time Protocol BCP              July 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  General Network Security Best Practices . . . . . . . . . . .   4
     2.1.  BCP 38  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  NTP Configuration Best Practices  . . . . . . . . . . . . . .   5
     3.1.  Keeping NTP Up to Date  . . . . . . . . . . . . . . . . .   5
     3.2.  Using Enough Time Sources . . . . . . . . . . . . . . . .   5
     3.3.  Using a Diversity of Reference Clocks . . . . . . . . . .   6
     3.4.  Control Messages  . . . . . . . . . . . . . . . . . . . .   7
     3.5.  Monitoring  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.6.  Using Pool Servers  . . . . . . . . . . . . . . . . . . .   8
     3.7.  Leap-Second Handling  . . . . . . . . . . . . . . . . . .   8
       3.7.1.  Leap Smearing . . . . . . . . . . . . . . . . . . . .   9
   4.  NTP Security Mechanisms . . . . . . . . . . . . . . . . . . .  10
     4.1.  Pre-Shared Key Approach . . . . . . . . . . . . . . . . .  11
     4.2.  Autokey . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.3.  Network Time Security . . . . . . . . . . . . . . . . . .  11
     4.4.  External Security Protocols . . . . . . . . . . . . . . .  12
   5.  NTP Security Best Practices . . . . . . . . . . . . . . . . .  12
     5.1.  Minimizing Information Leakage  . . . . . . . . . . . . .  12
     5.2.  Avoiding Daemon Restart Attacks . . . . . . . . . . . . .  13
     5.3.  Detection of Attacks through Monitoring . . . . . . . . .  14
     5.4.  Kiss-o'-Death Packets . . . . . . . . . . . . . . . . . .  15
     5.5.  Broadcast Mode Only on Trusted Networks . . . . . . . . .  15
     5.6.  Symmetric Mode Only with Trusted Peers  . . . . . . . . .  16
   6.  NTP in Embedded Devices . . . . . . . . . . . . . . . . . . .  16
     6.1.  Updating Embedded Devices . . . . . . . . . . . . . . . .  16
     6.2.  Server Configuration  . . . . . . . . . . . . . . . . . .  17
   7.  NTP over Anycast  . . . . . . . . . . . . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
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