[cifs-protocol] Registry Setting to change NTP clients not to run as 'symmetric active'

Hongwei Sun hongweis at microsoft.com
Wed Jun 11 16:26:53 GMT 2008


   In Window XP and Window 2003, the mode of client used to synchronize with time server is specified in registry key HKLM\SYSTEM\CurrentControlSet\Services\W32Time\Parameters\NtpServer.

   The setting contains time server name that may also be followed by a comma and a DWORD containing flags for special handling of that time source. If the flag is not specified, they default to 0x0. The available flags are:

 Instead of following the NTP specification, wait for the interval specified in the SpecialPollInterval entry before attempting to recontact this time source. Setting this flag decreases network usage, but it also decreases accuracy.

 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.

 Set the local computer to operate in symmetric active mode in the association with this source.

 Set the local computer to operate in client mode in the association with this source.

   If you set the flag to 0x08,  XP or Window2003 will run client mode , instead of "symmetric active" mode.

 Please see the following link for details



Hongwei  Sun - Support Escalation Engineer
DSC Protocol  Team, Microsoft
hongweis at microsoft.com
Tel:  469-7757027 x 57027

----Original Message-----

From: Andrew Bartlett [mailto:abartlet at samba.org]

Sent: Wednesday, May 28, 2008 12:42 AM

To: Interoperability Documentation Help

Cc: pfif at tridgell.net

Subject: NTP clients as 'symmetric active'

The MS-SNTP document claims that Microsoft's SNTP conforms with the NTP packet layout in 2.2, and in section 4, shows a client NTP packet with 'mode = 3' (first line of packet frame).

However, your client in WinXP and apparently win2003 acts as 'symmetric active'.  (mode = 1). This is described in the specification RFC1305 as:

 By operating in this mode the host announces its willingness to  synchronize and be synchronized by the peer.

However, WinXP clients typically do *not* have a hardware clock, and nor are they expected to be trusted as sources of time.  They should act as per the spec, and be 'clients', described in the RFC as:

 By operating in this mode the host, usually a LAN workstation,  announces its willingness to be synchronized by, but not to synchronize  the peer.

Google 'w32tm symmetic active' for the pain this is causing real users on the internet.

This violation of the RFC by your client implementation is making it harder for me to modify the standard ntp.org distribution to handle these requests.  (As well as simply not matching the docs you supply).

The use of mode 3 (client) is specified in RFC 4330 in section 5 'SNTP client operations'.


Andrew Bartlett


Andrew Bartlett


Authentication Developer, Samba Team           <http://samba.org>

Samba Developer, Red Hat Inc.

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