Internet DRAFT - draft-gruessing-ntp-ntpv5-requirements
draft-gruessing-ntp-ntpv5-requirements
Network Time Protocol J. Gruessing
Internet-Draft December 29, 2020
Intended status: Informational
Expires: July 2, 2021
NTPv5 use cases and requirements
draft-gruessing-ntp-ntpv5-requirements-01
Abstract
This document describes the use cases, requirements, and
considerations that should be factored in the design of a successor
protocol to supercede version 4 of the NTP protocol [RFC5905]
presently referred to as NTP version 5 ("NTPv5"). This document is
non-exhaustive and does not in its current version represent working
group consensus.
Note to Readers
_RFC Editor: please remove this section before publication_
Source code and issues for this draft can be found at
https://github.com/fiestajetsam/I-D/tree/main/draft-gruessing-ntp-
ntpv5-requirements [1].
Status of This Memo
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. Use cases and existing deployments of NTP . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. IP affinity . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Algorithms . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Timescales . . . . . . . . . . . . . . . . . . . . . . . 4
3.4. Leap seconds . . . . . . . . . . . . . . . . . . . . . . 4
3.4.1. Leap second smearing . . . . . . . . . . . . . . . . 4
3.5. Backwards compatibility to NTS and NTPv4 . . . . . . . . 4
3.6. Extensibility . . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
NTP version 4 [RFC5905] has seen active use for over a decade, and
within this time period the protocol has not only been extended to
support new requirements but also fallen victim to vulnerabilities
that have made it used for distributed denial of service (DDoS)
amplification attacks.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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2. Use cases and existing deployments of NTP
There are several common scenarios for exxisting NTPv4 deployments;
publicly accessible NTP services such as the NTP Pool [ntppool] are
used to offer clock synchronisation for end users and embedded
devices, ISP provided servers to synchronise devices such as
customer-premesis equipment where reduced accuracy may be tollerable.
Depending on the network and path these deployments may be affected
by variable latency as well as throttling or blocking by providers.
Data centres and cloud computing providers also have deployed and
offer NTP services both for internal use and for customers,
particularly where the network is unable to offer or does not require
PTP [IEEE-1588-2008]. As these deployments are less likely to be
constrained by network latency or power the potential for higher
levels of accuracy and precision within the bounds of the protocol
are possible.
3. Requirements
At a high level, NTPv5 should be a protocol that is capable of
operating in both local networks and also over public internet
connections where packet loss, delay, and even filtering may occur.
Timestamp resolution SHOULD either match or exceed NTPv4, and be
extensible to represent any specified timescale.
The protocol SHOULD NOT transmit time zone information and should
focus on providing clock synchronisation as TZDIST [RFC7808] already
provides this ability.
3.1. IP affinity
Servers SHOULD have a new identifier that peers use as reference,
this SHOULD NOT be a FQDN, an IP address, or identifier tied to a
certificate. Servers SHOULD be able to migrate and change their
identifiers as stratum topologies or network configuration changes
occur.
Clients SHOULD re-establish connections with servers at an interval
to prevent attempting to maintain connectivity to dead host and give
network operators the ability to move traffic away from IP addresses
in a timely manner. This functionality should also compliment having
a "Kiss of Death" or similar message from servers.
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3.2. Algorithms
Algorithms describing functions such as clock filtering, selection
and clustering SHOULD be omitted from the specification; the
specification should instead only provide only what is necessary to
describe protocol semantics and normative behaviours.
The working group should consider creating a separate informational
document to describe an algorithm to assist with implementation, and
to consider adopting future documents which describe new algorithms
as they are developed. Specifying client algorithms separately from
the protocol allows will allow NTPv5 to meet the needs of
applications with a variety of network properties and performance
requirements. It also allows for innovation in implementations
without sacrificing basic interoperability.
3.3. Timescales
Support SHOULD be available for other timescales in addition to UTC -
this should include, but not limited to the use of TAI or Modified
Julian Date as defined in [I-D.ietf-ntp-roughtime], however UTC SHALL
be the default timescale and MUST be supported by all
implementations. Consideration should be made to include listing the
supported timescales either as part of specific IANA parameter
registry, or as part of the extension registry.
3.4. Leap seconds
The specification or the protocol SHOULD be explicit about when a
leap second is being applied, and the protocol should allow for
transmiting an upcoming leap second ahead of the day it is to be
applicable. Nevertheless, due to network delays and the polling
interval, applications with NTP clients will need to manage the leap
second event at their local clock.
3.4.1. Leap second smearing
Server responses SHOULD include not only an indicator as to wether
the server supports smearing, but also if the current time being
transmitted is smeared. The protocol may also transmit the start/end
or duration of the smearing ahead of time. It MUST be possible for
clients to determine the unsmeared time of the timescale.
3.5. Backwards compatibility to NTS and NTPv4
The support for compatibility with other protocols SHOULD NOT prevent
addressing issues that have previous caused issues in deployments or
cause ossification of the protocol. Protocol ossification MUST be
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addressed to prevent existing NTPv4 deployments which incorrectly
respond to clients posing as NTPv5 from causing issues. Forward
prevention of ossification (for a potential NTPv6 protocol in the
future) SHOULD also be taken into consideration.
The model for backward compatibility is servers that support mutliple
versions NTP and send a response in the same version as the request.
This does not preclude high stratum servers from acting as a client
in one version of NTP and a server in another.
3.6. Extensibility
To provide the protocol MUST have the capability to be extended. The
specification should specify that implementations MUST ignore unknown
extensions. Unknown extensions received by a server from a lower
stratum server SHALL not be added to response messages sent by the
server receiving these extensions.
4. IANA Considerations
Considerations should be made about the future of the existing IANA
registry for NTPv4 parameters. If NTPv5 becomes incompatible with
these parameters a new registry SHOULD be created.
5. Security Considerations
Encryption and authentication MUST be provided by the protocol
specification as a default and MUST be resistent to downgrade
attacks. The encryption used must have agility, allowing for the
protocol to update as more secure cryptography becomes known and
vulnerabilities are discovered.
The specification MAY consider leaving room for middleboxes which may
deliberately modify packets in flight for legitimate purposes.
Thought must be given around how this will be incorporated into any
applicable trust model. Downgrading attacks that could lead to an
adversary disabling or removing encryption or authentication MUST NOT
be possible in the design of the protocol.
Detection and reporting of server malfeasence SHOULD remain out of
scope of this specification as [I-D.ietf-ntp-roughtime] already
provides this capability as a core functionality of the protocol.
--back
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6. Acknowledgements
The author would like to thank Doug Arnold for contributions to this
document, and would like to acknowledge Daniel Franke, Watson Ladd,
Miroslav Lichvar for their existing documents and ideas. The author
would also like to thank Angelo Moriondo, Franz Karl Achard, and
Malcom McLean for providing the author with motivation.
7. References
7.1. Normative References
[I-D.ietf-ntp-roughtime]
Malhotra, A., Langley, A., and W. Ladd, "Roughtime",
draft-ietf-ntp-roughtime-03 (work in progress), August
2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution
Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
<https://www.rfc-editor.org/info/rfc7808>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[IEEE-1588-2008]
"IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
n.d..
[ntppool] "pool.ntp.org: the internet cluster of ntp servers", n.d.,
<https://www.ntppool.org>.
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7.3. URIs
[1] https://github.com/fiestajetsam/I-D/tree/main/draft-gruessing-
ntp-ntpv5-requirements
Author's Address
James Gruessing
Email: james.ietf@gmail.com
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