[ntp:questions] Transmit timestamp older than receive timestamp...?

marco danti lupobuono64 at yahoo.com
Fri Dec 5 21:45:28 UTC 2014

Hi, looking at some sniffer traces I noticed NTP packets containing confusing timestamps like this:
Receive Timestamp : Jul 26, 2012 06:49:13.652482000 UTC   (T2)
Transmit Timestamp: Jul 26, 2012 06:49:13.652217000 UTC   (T3)

According to the above timestamps, that packet was transmitted *before* it was received.The messages sent by the server in question have correct timestamps most of the time, but every once in a while, a packet show up with T3 < T2.
I can't figure out  what could possibly explain this curious behaviour; on the other side, I wonder what would a client do upon reception of such a packet. My best guess is that it should be discarded.

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