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Showing posts from March, 2008

Network-focused analysis of the Windows Time Service

Due to some recent posts on the comp.protocols.time.ntp newsgroup, I took it upon myself to investigate the behavior of the Windows Time Service a bit further using the Wireshark protocol analyzer.

It appears that in Windows XP, 2003, and Vista, the Windows Time Service (w32time) will by default always try to form a "symmetric active" association with configured NTP servers. This can be problematic with some time servers, violates the published RFC-1305 specification, and is not necessary. I could find no explanation on Microsoft's site for this behavior; I suspect it has something to do with interoperability with older Windows 2000 domain controllers that had very broken NTP.

However, there is a simple workaround. You can simply add ",0x8" to the end of any configured time server, and Windows will only use a client-mode association. For example, the command:
w32tm /configure /manualpeerlist:"0.pool.ntp.org,0x8 1.pool.ntp.org,0x8 2.pool.ntp.org,0x8" /syn…