Network Time Protocol Best Current Practices
RFC 8633
| Document | Type |
RFC - Best Current Practice
(July 2019; No errata)
Also known as BCP 223
Was draft-ietf-ntp-bcp (ntp WG)
|
|
|---|---|---|---|
| Authors | Denis Reilly , Harlan Stenn , Dieter Sibold | ||
| 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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