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ntp: add client support for network correction

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If the network correction is known for both the request and response,
and their sum is not larger that the measured peer delay, allowing the
transparent clocks to be running up to 100 ppm faster than the client's
clock, apply the corrections to the NTP offset and peer delay. Don't
correct the root delay to not change the estimated maximum error.
This commit is contained in:
Miroslav Lichvar
2023-09-26 12:52:39 +02:00
parent 8eef631009
commit 70cdd8b1ef
10 changed files with 216 additions and 51 deletions
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24
doc/chrony.conf.adoc
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@@ -322,7 +322,9 @@ server implementations do not respond to requests containing an unknown
extension field (*chronyd* as a server responded to such requests since
version 2.0).
+
The following extension field can be enabled by this option:
This option can be used multiple times to enable multiple extension fields.
+
The following extension fields are supported:
+
_F323_::::
An experimental extension field to enable several improvements that were
@@ -331,6 +333,14 @@ root delay and dispersion in higher resolution and a monotonic receive
timestamp, which enables a frequency transfer between the server and client to
significantly improve stability of the synchronisation. This field should be
enabled only for servers known to be running *chronyd* version 4.2 or later.
_F324_::::
An experimental extension field to enable the use of the Precision Time
Protocol (PTP) correction field in NTP-over-PTP messages updated by one-step
end-to-end transparent clocks in network switches and routers to significantly
improve accuracy and stability of the synchronisation. NTP-over-PTP can be
enabled by the <<ptpport,*ptpport*>> directive and setting the *port* option to
the PTP port. This field should be enabled only for servers known to be running
*chronyd* version 4.5 or later.
{blank}:::
[[pool]]*pool* _name_ [_option_]...::
@@ -2727,8 +2737,10 @@ pidfile /run/chronyd.pid
The *ptpport* directive enables *chronyd* to send and receive NTP messages
contained in PTP event messages (NTP-over-PTP) to enable hardware timestamping
on NICs which cannot timestamp NTP packets, but can timestamp unicast PTP
packets. The port recognized by the NICs is 319 (PTP event port). The default
value is 0 (disabled).
packets, and also use corrections provided by PTP one-step end-to-end
transparent clocks in network switches and routers. The port recognized by the
NICs and PTP transparent clocks is 319 (PTP event port). The default value is 0
(disabled).
+
The NTP-over-PTP support is experimental. The protocol and configuration can
change in future. It should be used only in local networks.
@@ -2738,12 +2750,14 @@ server or client. The directive does not change the default protocol of
specified NTP sources. Each NTP source that should use NTP-over-PTP needs to
be specified with the *port* option set to the PTP port. To actually enable
hardware timestamping on NICs which can timestamp PTP packets only, the
*rxfilter* option of the *hwtimestamp* directive needs to be set to _ptp_.
*rxfilter* option of the *hwtimestamp* directive needs to be set to _ptp_. The
extension field _F324_ needs to be enabled to use the corrections provided by
the PTP transparent clocks.
+
An example of client configuration is:
+
----
server foo.example.net minpoll 0 maxpoll 0 xleave port 319
server foo.example.net minpoll 0 maxpoll 0 xleave port 319 extfield F324
hwtimestamp * rxfilter ptp
ptpport 319
----