W32Time: Windows Time Service

The mode that Windows Time uses {ed:by default?} to send requests is set by the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer

If the value of the Enabled entry in this subkey is 1, Windows Time uses symmetric active mode. Otherwise, Windows Time uses client mode.

To set the NTP servers used by the time service, type the following at the command prompt:

w32tm /config "/manualpeerlist:NTP_server,mode" /syncfromflags:MANUAL 
net stop w32time 
net start w32time 
w32tm /resync

Check the System event log for error messages.

Where "NTP_servers,mode" is the name of the NTP server seperated with a comma from the mode used to contact that server. Multiple server,mode pairs can be listed, seperated by a space. For example: "time.windows.com,0x1 time-b.timefreq.bldrdoc.gov,0x8 time.nist.gov,0x2 tick.usno.navy.mil,0x2". This string is stored in the registry at ..\W32Time\Parameters\NtpServer (not under "TimeProviders" as one might expect.)

Known time (NTP) servers: Also: http://tf.nist.gov/service/time-servers.html). Follow proper etiquette before using please.

time.windows.com Microsoft's time server
time-a.nist.gov Gaithersburg, Maryland
time-nw.nist.gov Redmond, Washington
time.nist.gov (ultra precise)
time-b.timefreq.bldrdoc.gov
nist1.symmetricom.com
tick.usno.navy.mil should not be used except as backup
tock.usno.navy.mil should not be used except as backup

The valid settings for the mode used with the /manualpeerlist switch include the following: ^

0x01 - use special poll interval set in registry at ..\W32Time\TimeProviders\NtpClient\SpecialPollInterval which must be a DWORD value in seconds. 900 decimal (every 15 minutes) is recommend.
0x02 - Use this time source only as a fallback. If all time sources that are not fallbacks have failed, then the system selects one fallback time source at random and uses it.
0x04 - send request as SymmetricActive mode. This mode is supported by Windows servers, but may not be supported by servers running other operating systems. KB875424
0x08 - send request as Client mode {ed: using the settings from \W32Time\TimeProviders\NtpClient\?}

The /syncfromflags:MANUAL flag in the W32TM command above specifies that the list of NTP servers provided should be used as a time source. This is appropriate for a standalone server or the main controller in a local domain. All other servers should be set to /syncfromflags:DOMHIER which causes the system to sync from the domain controller. This setting is stored at ..\W32Time\Parameters\Type and has the following possible values: ^

NoSync Does not synchronize time.
NTP Synchronizes time to the time sources specified in the Parameters\NtpServer entry. This is /syncfromflags:MANUAL
Nt5DS Synchronizes time to the domain hierarchy. i.e. /syncfromflags:DOMHIER
AllSync Uses all synchronization mechanisms available.