| [chrony-users] NTP over PTP |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: [chrony-users] NTP over PTP
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Thu, 19 Aug 2021 15:56:24 +0200
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There is a new experimental feature available in the latest code in
git. NTP messages can be exchanged as a payload of PTP messages to
enable hardware timestamping on NICs that can timestamp PTP messages,
but not NTP messages. This improves accuracy and stability of
synchronization while avoiding the security and other issues of PTP.
I tested it with three NICs: XL710 (i40e), BCM5720 (tg3) and BCM57810
(bnx2x). It works on the first two, but doesn't work on the third one.
It seems to check for the PTP multicast address in addition to the PTP
port, version and message type. This means it's unusable even for the
standard PTP unicast mode. I don't know if this limitation is in the
hardware or firmware (where it could potentially be fixed).
If anyone is willing to test the new code and has access to other NICs
which have a "ptpv2" filter but not the "all" filter listed in the
ethtool -T output, please let me know if it worked for you or not.
Both TX and RX timestamping printed by chronyc ntpdata should be
hardware and the stddev value in sourcestats should improve
significantly.
For example, synchronization between two BCM5720 using plain NTP:
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
==============================================================================
10.43.134.28 16 7 15 -0.006 0.275 -3ns 1312ns
and NTP-over-PTP:
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
==============================================================================
10.43.134.28 16 10 15 -0.000 0.019 -0ns 84ns
The new ptpport directive is documented here:
https://chrony.tuxfamily.org/doc/devel/chrony.conf.html#ptpport
--
Miroslav Lichvar
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