wdiff rfc9760v1.txt rfc9760.txt

Internet Engineering Task Force (IETF) D. Arnold
Request for Comments: 9760 Meinberg-USA
Category: Standards Track H. Gerstung
ISSN: 2070-1721 Meinberg
March
April 2025

Enterprise Profile for the Precision Time Protocol with Mixed Multicast
and Unicast Messages

Abstract

This document describes a Precision Time Protocol (PTP) Profile (IEEE
Standard 1588-2019) for use in an IPv4 or IPv6 Enterprise enterprise information
system environment. The PTP Profile uses the End-to-End delay
measurement mechanism, allowing both multicast and unicast Delay
Request and Delay Response messages.

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 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/rfc9760.

This document is subject to BCP 78 and the IETF Trust's Legal
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in the Revised BSD License.

Table of Contents

1. Introduction
2. Requirements Language
3. Technical Terms
4. Problem Statement
5. Network Technology
6. Time Transfer and Delay Measurement
7. Default Message Rates
8. Requirements for TimeTransmitter Clocks
9. Requirements for TimeReceiver Clocks
10. Requirements for Transparent Clocks
11. Requirements for Boundary Clocks
12. Management and Signaling Messages
13. Forbidden PTP Options
14. Interoperation with IEEE 1588 Default Profile
15. Profile Identification
16. IANA Considerations
17. Security Considerations
18. References
18.1. Normative References
18.2. Informative References
Acknowledgements
Authors' Addresses

1. Introduction

The Precision Time Protocol (PTP), standardized in IEEE 1588, has
been designed in its first version (IEEE 1588-2002) with the goal of
minimizing configuration on the participating nodes. Network
communication was based solely on multicast messages, which, unlike
NTP, did not require that a receiving node as discussed in IEEE
1588-2019 [IEEE1588-2019] need to know the identities of the time
sources in the network. This document describes clock roles and PTP
Port states using the optional alternative terms "timeTransmitter"
instead of "master" and "timeReceiver" instead of "slave", as defined
in the IEEE 1588g amendment [IEEE1588g] to [IEEE1588-2019].

The "Best TimeTransmitter Clock Algorithm" ([IEEE1588-2019],
Subclause 9.3), a mechanism that all participating PTP nodes Nodes MUST
follow, sets up strict rules for all members of a PTP domain to
determine which node MUST be the active reference time source
(Grandmaster). Although the multicast communication model has
advantages in smaller networks, it complicated the application of PTP
in larger networks -- for example, in environments like IP-based
telecommunication networks or financial data centers. It is
considered inefficient that, even if the content of a message applies
only to one receiver, the message is forwarded by the underlying
network (IP) to all nodes, requiring them to spend network bandwidth
and other resources, such as CPU cycles, to drop it.

The third edition of the standard (IEEE 1588-2019) defines PTPv2.1
and includes the possibility of using unicast communication between
the PTP nodes Nodes in order to overcome the limitation of using multicast
messages for the bidirectional information exchange between PTP
nodes.
Nodes. The unicast approach avoided that. In PTP domains with a lot
of nodes, devices had to throw away most of the received multicast
messages because they carried information for some other node. The
percent of PTP messages that are discarded as irrelevant to the
receiving node can exceed 99% [Estrela_and_Bonebakker].

PTPv2.1 also includes PTP Profiles ([IEEE1588-2019], Subclause 20.3).
These constructs allow organizations to specify selections of
attribute values and optional features, simplifying the configuration
of PTP nodes Nodes for a specific application. Instead of having to go
through all possible parameters and configuration options and
individually set them up, selecting a PTP Profile on a PTP node Node will
set all the parameters that are specified in the PTP Profile to a
defined value. If a PTP Profile definition allows multiple values
for a parameter, selection of the PTP Profile will set the profile-
specific default value for this parameter. Parameters not allowing
multiple values are set to the value defined in the PTP Profile.
Many PTP features and functions are optional, and a PTP Profile
should also define which optional features of PTP are required,
permitted, and prohibited. It is possible to extend the PTP standard
with a PTP Profile by using the TLV mechanism of PTP (see
[IEEE1588-2019], Subclause 13.4), 13.4) or defining an optional Best
TimeTransmitter Clock Algorithm, and a few among other ways. techniques (which are
beyond the scope of this document). PTP has its own management
protocol (defined in [IEEE1588-2019], Subclause 15.2) but allows a
PTP Profile to specify an alternative management mechanism -- for
example, the Network Configuration Protocol (NETCONF).

In this document, the term "PTP Port" refers to a logical access
point of a PTP instantiation for PTP communication in a network.

2. Requirements Language

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.

3. Technical Terms

Acceptable TimeTransmitter Table: A list of timeTransmitters that
may be maintained by a PTP timeReceiver Clock. The PTP
timeReceiver Clock would be willing to synchronize to
timeTransmitters in this list.

Alternate timeTransmitter: A PTP timeTransmitter Clock, which Clock that is not
the Best timeTransmitter, timeTransmitter and therefore is used as an alternative
clock. It may act as a timeTransmitter with the Alternate
timeTransmitter flag set on the messages it sends.

Announce message: Contains the timeTransmitter Clock properties of a given timeTransmitter
Clock. The information is used to determine the Best TimeTransmitter.
timeTransmitter.

Best timeTransmitter: A clock with a PTP Port in the timeTransmitter
state, operating as the Grandmaster of a PTP domain.

Best TimeTransmitter Clock Algorithm: A method for determining which
state a PTP Port of a PTP clock should be in. The state decisions
lead to the formation of a clock spanning tree for a PTP domain.

Boundary Clock: A device with more than one PTP Port. Generally,
Boundary Clocks will have one PTP Port in the timeReceiver state
to receive timing and other PTP Ports in the timeTransmitter state
to redistribute the timing.

Clock Identity: In [IEEE1588-2019], a 64-bit number assigned to each
PTP clock. This number MUST be globally unique. Often, it is
derived from the Ethernet Media Access Control (MAC) address.

Domain: Treated as a separate PTP system in a network. Every PTP
message contains a domain number. Clocks, however, can combine
the timing information derived from multiple domains.

End-to-End delay measurement mechanism: A network delay measurement
mechanism in PTP facilitated by an exchange of messages between a
timeTransmitter Clock and a timeReceiver Clock. These messages
might traverse Transparent Clocks and PTP-unaware switches. This
mechanism might not work properly if the Sync and Delay Request
messages traverse different network paths.

Grandmaster: The timeTransmitter Clock that is currently acting as
the reference time source of the PTP domain.

IEEE 1588: The timing and synchronization standard that defines PTP
and describes the node, system, and communication properties
necessary to support PTP.

NTP: Network Time Protocol, defined by [RFC5905].

Ordinary Clock: A clock that has a single PTP Port in a domain and
maintains the timescale used in the domain. It may serve as a
timeTransmitter Clock or may be a timeReceiver Clock.

Peer-to-Peer delay measurement mechanism: A network delay
measurement mechanism in PTP facilitated by an exchange of
messages over the link between adjacent devices in a network.
This mechanism might not work properly unless all devices in the
network support PTP and the Peer-to-peer Peer-to-Peer delay measurement
mechanism.

Preferred timeTransmitter: A device intended to act primarily as the
Grandmaster of a PTP system or as a backup to a Grandmaster.

PTP: The Precision Time Protocol -- the timing and synchronization
protocol defined by IEEE 1588.

PTP Port: An interface of a PTP clock with the network. Note that
there may be multiple PTP Ports running on one physical interface
-- for example, multiple unicast timeReceivers that talk to
several Grandmaster Clocks in different PTP Domains. domains.

PTP Profile: A set of constraints on the options and features of
PTP, designed to optimize PTP for a specific use case or industry.
The profile specifies what is required, allowed, and forbidden
among options and attribute values of PTP.

PTPv2.1: Refers specifically to the version of PTP defined by
[IEEE1588-2019].

Rogue timeTransmitter: A clock with that has a PTP Port in the
timeTransmitter state, state -- even though it should not be in the
timeTransmitter state according to the Best TimeTransmitter Clock
Algorithm,
Algorithm -- and that does not set the Alternate timeTransmitter
flag.

TimeReceiver Clock: A clock with at least one PTP Port in the
timeReceiver state and no PTP Ports in the timeTransmitter state.

TimeReceiver Only only clock: An Ordinary Clock that cannot become a
timeTransmitter Clock.

TimeTransmitter Clock: A clock with at least one PTP Port in the
timeTransmitter state.

TLV: Type Length Value -- a mechanism for extending messages in
networked communications.

Transparent Clock: A device that measures the time taken for a PTP
event message to transit the device and then updates the message
with a correction for this transit time.

Unicast Discovery: A mechanism for PTP timeReceivers to establish a
unicast communication with PTP timeTransmitters using a configured
table of timeTransmitter IP addresses and unicast message
negotiation.

Unicast Message
Negotiation.

Unicast Negotiation: message negotiation: A mechanism in PTP for timeReceiver
Clocks to negotiate unicast Sync, Announce, and Delay Request
message transmission rates from timeTransmitters.

4. Problem Statement

This document describes how PTP can be applied to work in large
enterprise networks. See ISPCS [RFC2026] for information on IETF
applicability statements. Such large networks are deployed, for
example, in financial corporations. It is becoming increasingly
common in such networks to perform distributed time-tagged
measurements, such as one-way packet latencies and cumulative delays
on software systems spread across multiple computers. Furthermore,
there is often a desire to check the age of information time-tagged
by a different machine. To perform these measurements, it is
necessary to deliver a common precise time to multiple devices on a
network. Accuracy currently required in the financial industry
ranges from 100 microseconds to 1 nanosecond to the Grandmaster.
This PTP Profile does not specify timing performance requirements,
but such requirements explain why the needs cannot always be met by
NTP as commonly implemented. Such accuracy cannot usually be
achieved with a traditional time transfer such as NTP, without adding non-standard customizations such as
on-path support, similar to what is done in PTP with Transparent
Clocks and Boundary Clocks. Such PTP support is commonly available
in switches and routers, and many such devices have already been
deployed in networks. Because PTP has a complex range of features
and options, it is necessary to create a PTP Profile for enterprise
networks to achieve interoperability among equipment manufactured by
different vendors.

Although enterprise networks can be large, it is becoming
increasingly common to deploy multicast protocols, even across
multiple subnets. For this reason, it is desirable to make use of
multicast whenever the information going to many destinations is the
same. It is also advantageous to send information that is only
relevant to one device as a unicast message. The latter can be
essential as the number of PTP timeReceivers becomes hundreds or
thousands.

PTP devices operating in these networks need to be robust. This
includes the ability to ignore PTP messages that can be identified as
improper and to have redundant sources of time.

Interoperability among independent implementations of this PTP
Profile has been demonstrated at the International Symposium on
Precision Clock Synchronization (ISPCS) Plugfest [ISPCS].

5. Network Technology

This PTP Profile MUST operate only in networks characterized by UDP
[RFC0768] over either IPv4 [RFC0791] or IPv6 [RFC8200], as described
by Annexes C and D of [IEEE1588-2019], respectively. A network node
MAY include multiple PTP instances running simultaneously. IPv4 and
IPv6 instances in the same network node MUST operate in different PTP
Domains.
domains. PTP Clocks clocks that communicate using IPv4 can transfer time to
PTP Clocks clocks using IPv6, or the reverse, if and only if there is a
network node that simultaneously communicates with both PTP domains
in the different IP versions.

The PTP system MAY include switches and routers. These devices MAY
be Transparent Clocks, Boundary Clocks, or neither, in any
combination. PTP Clocks clocks MAY be Preferred timeTransmitters, Ordinary
Clocks, or Boundary Clocks. The Ordinary Clocks may be TimeReceiver
Only Clocks timeReceiver
only clocks or may be timeTransmitter capable.

Note that PTP Ports will need to keep track of the Clock ID of
received messages and not just the IP or Layer 2 addresses in any
network that includes Transparent Clocks or that might include them
in the future. This is important, since Transparent Clocks might
treat PTP messages that are altered at the PTP application layer as
new IP packets and new Layer 2 frames when the PTP messages are
retransmitted. In IPv4 networks, some clocks might be hidden behind
a NAT, which hides their IP addresses from the rest of the network.
Note also that the use of NATs may place limitations on the topology
of PTP networks, Networks, depending on the port forwarding scheme employed.
Details of implementing PTP with NATs are out of scope for this
document.

PTP, similar to NTP, assumes that the one-way network delay for Sync
messages and Delay Response messages is the same. When this is not
true, it can cause errors in the transfer of time from the
timeTransmitter to the timeReceiver. It is up to the system
integrator to design the network so that such effects do not prevent
the PTP system from meeting the timing requirements. The details of
network asymmetry are outside the scope of this document. See, for
example, ITU-T G.8271 [G8271].

6. Time Transfer and Delay Measurement

TimeTransmitter Clocks, Transparent Clocks, and Boundary Clocks MAY
be either one-step clocks or two-step clocks. TimeReceiver Clocks
MUST support both behaviors. The End-to-End Delay delay measurement method
MUST be used.

Note that, in IP networks, Sync messages and Delay Request messages
exchanged between a timeTransmitter and timeReceiver do not
necessarily traverse the same physical path. Thus, wherever
possible, the network SHOULD be engineered so that the forward and
reverse routes traverse the same physical path. Traffic engineering
techniques for path consistency are out of scope for this document.

Sync messages MUST be sent as PTP event multicast messages (UDP port
319) to the PTP primary IP address. Two-step clocks MUST send
Follow-up messages as PTP general multicast messages (UDP port 320).
Announce messages MUST be sent as PTP general multicast messages (UDP
port 320) to the PTP primary address. The PTP primary IP address is
224.0.1.129 for IPv4 and FF0X:0:0:0:0:0:0:181 for IPv6, where "X" can
be a value between 0x0 and 0xF. The different IPv6 address options
are explained in [IEEE1588-2019], Annex D, Section D.3. These
addresses are allotted by IANA; see the "IPv6 Multicast Address Space
Registry" [IPv6Registry].

Delay Request messages MAY be sent as either multicast or unicast PTP
event messages. TimeTransmitter Clocks MUST respond to multicast
Delay Request messages with multicast Delay Response PTP general
messages. TimeTransmitter Clocks MUST respond to unicast Delay
Request PTP event messages with unicast Delay Response PTP general
messages. This allows for the use of Ordinary Clocks that do not
support the Enterprise Profile, if they are timeReceiver Only Clocks. only clocks.

Clocks SHOULD include support for multiple domains. The purpose is
to support multiple simultaneous timeTransmitters for redundancy.
Leaf devices (non-forwarding devices) can use timing information from
multiple timeTransmitters by combining information from multiple
instantiations of a PTP stack, each operating in a different PTP
Domain. Redundant
domain. To check for faulty timeTransmitter Clocks, redundant
sources of timing can be ensembled evaluated as an ensemble and/or compared
to check for faulty timeTransmitter Clocks.
individually. The use of multiple simultaneous timeTransmitters will
help mitigate faulty timeTransmitters reporting as healthy, network
delay asymmetry, and security problems. Security problems include
on-path attacks such as delay attacks, packet interception/manipulation interception attacks,
and packet manipulation attacks. Assuming that the path to each
timeTransmitter is different, failures -- malicious or otherwise --
would have to happen at more than one path simultaneously. Whenever
feasible, the underlying network transport technology SHOULD be
configured so that timing messages in different domains traverse
different network paths.

7. Default Message Rates

The Sync, Announce, and Delay Request default message rates MUST each
be once per second. The Sync and Delay Request message rates MAY be
set to other values, but not less than once every 128 seconds and not
more than 128 messages per second. The Announce message rate MUST
NOT be changed from the default value. The Announce Receipt Timeout
Interval MUST be three Announce Intervals for Preferred
TimeTransmitters
timeTransmitters and four Announce Intervals for all other
timeTransmitters.

The logMessageInterval carried in the unicast Delay Response message
MAY be set to correspond to the timeTransmitter ports ports' preferred
message period, rather than 7F, which indicates that message periods
are to be negotiated. Note that negotiated message periods are not
allowed; see Section 13 ("Forbidden PTP Options").

8. Requirements for TimeTransmitter Clocks

TimeTransmitter Clocks MUST obey the standard Best TimeTransmitter
Clock Algorithm as defined in [IEEE1588-2019]. PTP systems using
this PTP Profile MAY support multiple simultaneous Grandmasters if
each active Grandmaster is operating in a different PTP domain.

A PTP Port of a clock MUST NOT be in the timeTransmitter state unless
the clock has a current value for the number of UTC leap seconds.

If a unicast negotiation signaling message is received, it MUST be
ignored.

In PTP Networks that contain Transparent Clocks, timeTransmitters
might receive Delay Request messages that no longer contain the IP
addresses of the timeReceivers. This is because Transparent Clocks
might replace the IP address of Delay Requests with their own IP
address after updating the Correction Fields. For this deployment
scenario, timeTransmitters will need to have configured tables of
timeReceivers' IP addresses and associated Clock Identities in order
to send Delay Responses to the correct PTP Nodes.

9. Requirements for TimeReceiver Clocks

In a network that contains multiple timeTransmitters in multiple
domains, TimeReceivers timeReceivers SHOULD make use of information from all the
timeTransmitters in their clock control subsystems. TimeReceiver
Clocks MUST be able to function in such networks even if they use
time from only one of the domains. TimeReceiver Clocks MUST be able
to operate properly in the presence of a rogue timeTransmitter.
TimeReceivers SHOULD NOT synchronize to a timeTransmitter that is not
the Best TimeTransmitter timeTransmitter in its domain. TimeReceivers will continue
to recognize a Best TimeTransmitter timeTransmitter for the duration of the Announce
Time Out
Receipt Timeout Interval. TimeReceivers MAY use an Acceptable
TimeTransmitter Table. If a timeTransmitter is not an Acceptable
timeTransmitter, then the timeReceiver MUST NOT synchronize to it.
Note that IEEE 1588-2019 requires timeReceiver Clocks to support both
two-step and one-step timeTransmitter Clocks. See [IEEE1588-2019],
Subclause 11.2.

Since Announce messages are sent as multicast messages, timeReceivers
can obtain the IP addresses of a timeTransmitter from the Announce
messages. Note that the IP source addresses of Sync and Follow-up
messages might have been replaced by the source addresses of a
Transparent Clock; therefore, timeReceivers MUST send Delay Request
messages to the IP address in the Announce message. Sync and Follow-
up messages can be correlated with the Announce message using the
Clock ID, which is never altered by Transparent Clocks in this PTP
Profile.

10. Requirements for Transparent Clocks

Transparent Clocks MUST NOT change the transmission mode of an
Enterprise Profile PTP message. For example, a Transparent Clock
MUST NOT change a unicast message to a multicast message.
Transparent Clocks that syntonize to the timeTransmitter Clock might
need to maintain separate clock rate offsets for each of the
supported domains.

11. Requirements for Boundary Clocks

Boundary Clocks SHOULD support multiple simultaneous PTP domains.
This will require them to maintain separate clocks for each of the
domains supported, at least in software. Boundary Clocks MUST NOT
combine timing information from different domains.

12. Management and Signaling Messages

PTP Management management messages MAY be used. Management messages intended
for a specific clock, i.e., where the
targetPortIdentity.clockIdentity attribute (defined in
[IEEE1588-2019]) is does not have all bits set to All 1s, 1, MUST be sent as a
unicast message. Similarly, if any signaling messages are used, they
MUST also be sent as unicast messages whenever the message is
intended solely for a specific PTP Node.

13. Forbidden PTP Options

Clocks operating in the Enterprise Profile MUST NOT use the
following:

* Peer-to-Peer timing for delay measurement

* Grandmaster Clusters

* The Alternate TimeTransmitter timeTransmitter option

* Alternate Timescales

* Unicast discovery

* Unicast message negotiation

Clocks operating in the Enterprise Profile MUST avoid any optional
feature that requires Announce messages to be altered by Transparent
Clocks, as this would require the Transparent Clock to change the
source address and prevent the timeReceiver nodes from discovering
the protocol address of the timeTransmitter.

14. Interoperation with IEEE 1588 Default Profile

Clocks operating in the Enterprise Profile will interoperate with
clocks operating in the Default Profile described in [IEEE1588-2019],
Annex I.3. This variant of the Default Profile uses the End-to-End
delay measurement mechanism. In addition, the Default Profile would
have to operate over IPv4 or IPv6 networks and use management
messages in unicast when those messages are directed at a specific
clock. If neither of these requirements is met, then Enterprise
Profile clocks will not interoperate with Default Profile Clocks clocks as
defined in [IEEE1588-2019], Annex I.3. The Enterprise Profile will
not interoperate with the variant of the Default Profile defined in
[IEEE1588-2019], Annex I.4, which requires the use of the Peer-to-
Peer delay measurement mechanism.

Enterprise Profile Clocks clocks will interoperate with clocks operating in
other PTP Profiles if the clocks in the other PTP Profiles obey the
rules of the Enterprise Profile. These rules MUST NOT be changed to
achieve interoperability with other PTP Profiles.

15. Profile Identification

The IEEE 1588 standard requires that all PTP Profiles provide the
following identifying information.

PTP Profile: Enterprise Profile
Profile number: 1
Version: 1.0
Profile identifier: 00-00-5E-01-01-00

This PTP Profile was specified by the IETF.

A copy may be obtained at <https://datatracker.ietf.org/wg/tictoc/
documents>.

16. IANA Considerations

This document has no IANA actions.

17. Security Considerations

Protocols used to transfer time, such as PTP and NTP, can be
important to security mechanisms that use time windows for keys and
authorization. Passing time through the networks poses a security
risk, since time can potentially be manipulated. The use of multiple
simultaneous timeTransmitters, using multiple PTP domains, can
mitigate problems from rogue timeTransmitters and on-path attacks.
Note that Transparent Clocks alter PTP content on-path, but in a
manner specified in [IEEE1588-2019] that helps with time transfer
accuracy. See Sections 9 and 10. Additional security mechanisms are
outside the scope of this document.

PTP native management messages SHOULD NOT be used, due to the lack of a
security mechanism for this option. Secure management can be
obtained using standard management mechanisms that include security
-- for example, NETCONF [RFC6241].

General security considerations related to time protocols are
discussed in [RFC7384].

18. References

18.1. Normative References

[IEEE1588-2019]
IEEE, "IEEE Standard for a Precision Clock Synchronization
for Networked Measurement and Control Systems", IEEE
Std 1588-2019, DOI 10.1109/IEEESTD.2020.9120376, June
2020, <https://ieeexplore.ieee.org/document/9120376>.

[IEEE1588g]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems
Amendment 2: Master-Slave Optional Alternative
Terminology", IEEE Std 1588g-2022,
DOI 10.1109/IEEESTD.2023.10070440, March 2023,
<https://ieeexplore.ieee.org/document/10070440>.

[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.

[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>.

[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>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

18.2. Informative References

[Estrela_and_Bonebakker]
Estrela, P. and L. Bonebakker, "Challenges deploying PTPv2
in a global financial company", Proceedings of the IEEE
International Symposium on Precision Clock Synchronization
for Measurement, Control and Communication, pp. 1-6,
DOI 10.1109/ISPCS.2012.6336634, September 2012,
<https://www.researchgate.net/publication/260742322_Challe
nges_deploying_PTPv2_in_a_global_financial_company>.

[G8271] ITU-T, "Time and phase synchronization aspects of
telecommunication networks", ITU-T
Recommendation G.8271/Y.1366, March 2020,
<https://www.itu.int/rec/T-REC-G.8271-202003-I/en>.

[IPv6Registry]
IANA, "IPv6 Multicast Address Space Registry",
<https://iana.org/assignments/ipv6-multicast-addresses>.

[ISPCS] Arnold, D., "Plugfest Report", October D. and K. Harris, "Plugfest", Proceedings of the
IEEE International Symposium on Precision Clock
Synchronization for Measurement, Control, and
Communication (ISPCS), August 2017,
<https://www.ispcs.org>.
<https://2017.ispcs.org/plugfest>.

[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<https://www.rfc-editor.org/info/rfc2026>.

[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>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.

[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.

Acknowledgements

The authors would like to thank Richard Cochran, Kevin Gross, John
Fletcher, Laurent Montini, and many other members of the IETF for
reviewing and providing feedback on this document.

Authors' Addresses

Doug Arnold
Meinberg-USA
3 Concord Rd
Shrewsbury, Massachusetts 01545
United States of America
Email: doug.arnold@meinberg-usa.com

Heiko Gerstung
Meinberg
Lange Wand 9
31812 Bad Pyrmont
Germany
Email: heiko.gerstung@meinberg.de