'WARNING: NTPClock: 680: system clock apparently no longer synchronized to upstream time servers' on ESXi

Products

• VMware vSphere ESXi

Issue/Introduction

• There may be similar messages in /var/log/vmkwarning.log

WARNING: NTPClock: 680: system clock apparently no longer synchronized to upstream time servers

• NTP configuration is correct but observed that 'delay', 'offset' and 'jitter' are high. For example:

[root@esxi]: ntpq -p
   remote     refid  st  t when poll reach delay  offset   jitter
========================================================================
 *<NTP-Server>  .BD.   1  u 35  64   377   2.706  +1073.6  117.229

• The 'rootdisp' of NTP variables associated with this host is high. For example:

[root@esxi]: ntpq -c associate
ind assid  status  conf reach  auth condition   last_event cnt
===================================================================
1   7023   96fa    yes  yes    none sys.peer    sys_peer   15

[root@esxi]: ntpq -c "rv 7023"
associd=7023 status=96fa conf, reach, sel_sys.peer, 15 events, sys_peer,
srcadr=##.##.##.##, srcport=123, dstadr=##.##.##.##, dstport=123,
leap=00, stratum=1, precision=-13, rootdelay=0.000, rootdisp=10682.327,
refid=BD, reftime=eb61175d.b0a783e8 <Day, Month date year Time>,
rec=eb61175e.75b6c16b <Day, Month date year Time>, reach=377,
unreach=0, hmode=3, pmode=4, hpoll=10, ppoll=10, headway=0, flash=00 ok,
keyid=0, offset=+1073.6, delay=4.780, dispersion=15.386, jitter=117.229,
xleave=0.080,
filtdelay= 4.78  6.44  5.22  5.21  4.18  5.03  4.86  4.50,
filtoffset= -3.24  -3.73  -3.48  -3.14  -3.03  -2.60  -2.36  -2.15,
filtdisp= 18.12  15.83  31.94  47.60  63.75  79.14  94.76  110.58

Environment

vSphere ESXi 7.0.3
vSphere ESXi 8.x

Cause

By default, an unsynced Windows server chooses a 10-second dispersion and adds to the dispersion on each poll interval that it remains in sync. An ESXi host, by default, does not accept any NTP reply with a root dispersion greater than 1.5 seconds.

Resolution

To fix the issue by using one of the below options:

• Add 'tos maxdist 30' and 'iburst minpoll 3 maxpoll 4' parameters for NTP settings on ESXi from the KB vSphere ESXi 7.0 U3 and later versions NTP configuration steps loading a text file containing NTP configuration commands
• Change the 'root dispersion' on NTP server to 0. For example:
  The NTP server is a Windows server. Then change the below registry:
  "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\LocalClockDispersion" from 10 to 0