Some versions of the w32time service, especially those who are coming with Windows XP, or Windows Server 2003, may be (by default) unable to query the time from some NTP servers. Depending on the type of the Windows PC (eg. standalone server or domain controller), NTP servers may not respond to the type of queries sent by w32time. This is due to the type of request packets.

This problem has not been observed with the w32time version which has been shipped with Windows 2000. Also, the w32tm commands mentioned below can not be used under Windows 2000 since the basic functions of the w32tm utility have been changed for Windows versions after Windows 2000.

NTP supports several different packet types. Normally, (S)NTP clients send "client" mode request packets to a NTP server responding with a "server" mode packet. In the case mentioned above, the w32time service sends "symmetric active" instead of "client" mode packets to a NTP server. This type of packets has been implemented to support NTP's peering feature.

Peering means that a pool of computers ("peers") with "good" clocks have been configured to synchronize their clocks among each others, in order to agree on a common "network time", which then can be supplied to their clients. If a peer sends a "symmetric active" packet, it is willing to modify the NTP server's time. Of course the NTP server should not accept such requests from a "normal" client.

A standard NTP server ignores such packets, unless it has been explicitely configured to do so, and the sender can be authenticated as a configured peer. Recent versions of NTP have a build-in workaround which lets it send a reply, though, but don't really accept the w32time service as peer.

Using some commands in a command line window, the behaviour of w32time can be changed so that w32time sends the correct "client" mode request packets. The changes are saved permanently in the Windows registry:

w32tm /config /manualpeerlist:,0x8 /syncfromflags:MANUAL

Of course, the actual IP address of the NTP server or its host name must be entered instead of .

The flag "0x8" forces w32time not to send "symmetric active" packets but normal "client" requests which the NTP server replies to as usual.

Then following command can be used to immediately make the changes effective:

w32tm /config /update

Alternatively, the w32time service can be restarted:

net stop w32time net start w32time

The command

net time /querysntp

can be used to check the configuration. The output should look similar to the line below:

The current SNTP value is: ,0x8

If the w32time service is restarted it sends immediately a request to the NTP server. Additionally, the command

w32tm /resync

can be used to let w32time send a request.