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NTP server periodically desyncs

Posted on 2013-06-04
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Last Modified: 2013-12-02
Some time ago our NTP server (on Win SBS 2011 Std) started to desync occasionally. It can get 8 minutes slow overnight. Then after running w32tm /resync /rediscover it works fine for some time.
Configuration and status output (sorry that some of it is messed up. SBS doesn't allow changing the output language once it's been set up):
PS C:\Windows\system32> w32tm /query /configuration /verbose
[¿¿¿¿¿¿¿¿¿]

EventLogFlags: 2 (¿¿¿¿¿¿¿¿)
AnnounceFlags: 5 (¿¿¿¿¿¿¿¿)
TimeJumpAuditOffset: 28800 (¿¿¿¿¿¿¿¿)
MinPollInterval: 6 (¿¿¿¿¿¿¿¿)
MaxPollInterval: 10 (¿¿¿¿¿¿¿¿)
MaxNegPhaseCorrection: 3600 (¿¿¿¿¿¿¿¿)
MaxPosPhaseCorrection: 3600 (¿¿¿¿¿¿¿¿)
MaxAllowedPhaseOffset: 300 (¿¿¿¿¿¿¿¿)

FrequencyCorrectRate: 4 (¿¿¿¿¿¿¿¿)
PollAdjustFactor: 5 (¿¿¿¿¿¿¿¿)
LargePhaseOffset: 50000000 (¿¿¿¿¿¿¿¿)
SpikeWatchPeriod: 900 (¿¿¿¿¿¿¿¿)
LocalClockDispersion: 10 (¿¿¿¿¿¿¿¿)
HoldPeriod: 5 (¿¿¿¿¿¿¿¿)
PhaseCorrectRate: 7 (¿¿¿¿¿¿¿¿)
UpdateInterval: 100 (¿¿¿¿¿¿¿¿)

FileLogName:  (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogEntries:  (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogSize: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
FileLogFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)

[TimeProviders]

NtpClient (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\system32\w32time.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 1 (¿¿¿¿¿¿¿¿)
CrossSiteSyncFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)
AllowNonstandardModeCombinations: 1 (¿¿¿¿¿¿¿¿)
ResolvePeerBackoffMinutes: 15 (¿¿¿¿¿¿¿¿)
ResolvePeerBackoffMaxTimes: 7 (¿¿¿¿¿¿¿¿)
CompatibilityFlags: 2147483648 (¿¿¿¿¿¿¿¿)
EventLogFlags: 1 (¿¿¿¿¿¿¿¿)
LargeSampleSkew: 3 (¿¿¿¿¿¿¿¿)
SpecialPollInterval: 900 (¿¿¿¿¿¿¿¿)
Type: NTP (¿¿¿¿¿¿¿¿)
NtpServer: time.windows.com,0x1 (¿¿¿¿¿¿¿¿)

NtpServer (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\system32\w32time.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 0 (¿¿¿¿¿¿¿¿)
AllowNonstandardModeCombinations: 1 (¿¿¿¿¿¿¿¿)
EventLogFlags: 0 (¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿ ¿¿ ¿¿¿¿¿¿¿¿¿¿¿¿)

VMICTimeProvider (¿¿¿¿¿¿¿¿)
DllName: C:\Windows\System32\vmictimeprovider.dll (¿¿¿¿¿¿¿¿)
Enabled: 1 (¿¿¿¿¿¿¿¿)
InputProvider: 1 (¿¿¿¿¿¿¿¿)

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PS C:\Windows\system32> w32tm /query /status /verbose
¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 0(¿¿¿¿¿¿¿¿¿¿¿¿¿¿ ¿¿¿)
¿¿¿¿¿¿: 3 (¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿ - ¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿¿ ¿ ¿¿¿¿¿¿¿ (S)NTP)
¿¿¿¿¿¿¿¿: -6 (15.625ms ¿¿ ¿¿¿¿ ¿¿¿¿¿¿¿)
¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 0.2534276s
¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿: 6.2850124s
ReferenceId: 0x40040A21 (IP-¿¿¿¿¿ ¿¿¿¿¿¿¿¿¿:  64.4.10.33)
Last Successful Sync Time: 05.06.2013 9:19:51
Source: time.windows.com,0x1
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿: 6 (64s)

¿¿¿¿¿¿¿¿ ¿¿¿¿: 0.0000678s
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 0.0156121s
¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 3 (¿¿¿¿¿)
¿¿¿¿¿ ¿¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿¿: 0 (¿¿¿)
Server Role: 576 (¿¿¿¿¿¿¿¿ ¿¿¿¿¿¿ ¿¿¿¿¿¿¿)
Last Sync Error: 2 (The computer did not resync because only stale time data was available.)
Time since Last Good Sync Time: 162.4468032s

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It says Last Successful Sync Time: 05.06.2013 9:19:51 but I checked shortly after this time and it was 8 minutes slow. Yesterday everything was okay. The server is the only time server and DC in our domain.
Why does this happen?
Thank you.
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Question by:PavelTMN
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5 Comments
 
LVL 24

Expert Comment

by:Nagendra Pratap Singh
ID: 39221569
Is it virtual?

Do you have any other time-sync tools installed on it?
0
 
LVL 1

Author Comment

by:PavelTMN
ID: 39221629
No, it's not virtual and there aren't any time-sync tools except built-in ones.
0
 
LVL 14

Accepted Solution

by:
frankhelk earned 2000 total points
ID: 39224840
Hmm - I've had hassle with W32time in NTP mode whenever I used it.

My recommendation would be to just disable W32time and use "the real thing" - a Windows port of the standard NTP implementation. See here for a list.

Furthermore I would recommend to use the service at pool.ntp.org for a selection of time servers. Try these time server entries in your ntp.conf:
server 0.pool.ntp.org iburst
server 1.pool.ntp.org iburst
server 2.pool.ntp.org iburst
server 3.pool.ntp.org iburst

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0
 
LVL 1

Author Comment

by:PavelTMN
ID: 39227907
I would recommend to use the service at pool.ntp.org
I changed the NTP server to one suggested by you and so far the errors have disappeared along with skewing.
w32tm /config /syncfromflags:manual /manualpeerlist:3.ru.pool.ntp.org
w32tm /config /update
w32tm /resync
0
 
LVL 14

Expert Comment

by:frankhelk
ID: 39228201
Just to improve the quality of the NTP service even further, I would recommend to supply more server entries. That way W32time (if you persist to cling to it ...) or ntpd (the native NTP daemon) would be able to choose the best time source from a group of servers.

Just try

w32tm /config /syncfromflags:manual /manualpeerlist:0.ru.pool.ntp.org,1.ru.pool.ntp.org,2.ru.pool.ntp.org,3.ru.pool.ntp.org
w32tm /config /update
w32tm /resync

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