[Winpcap-users] FW: [Wireshark-users] FW: Dumpcap timestamp discrepancy

Phil Paradis Phil.Paradis at unitedtote.com
Wed Apr 15 23:58:57 PDT 2009

I was referred here from the wireshark-users list; here's the original post:

Phil Paradis wrote:
> We have a sniffer running continuously in one of our facilities, capturing
> data to/from a specific system. The box is running Windows XP Pro (SP-3) and
> dumpcap is running as a service using srvany.exe. The clock on this system is
> synchronized with the rest of the hosts on this network.
> When left running for an extended period of time (weeks/months) it seems the
> timestamps recorded in our captures slowly drift backwards. The timestamp
> recorded in the filename as each new file is created matches the system time
> relatively well (from observation; i.e. when BAT_99717_20090415222212.cap was
> created, the system clock showed 10:22 PM.) however the packet timestamps
> within the file are off by a significant amount. (In this particular example,
> the first packet in the file has a timestamp of 22:16:18, nearly 6 minutes
> earlier than when the file was opened.)
> Stopping and restarting the service seems to correct this; after a restart,
> the first packet in the new file had a timestamp closely matching the
> timestamp in the filename (and the system time.)
> What documentation I can find seems to indicate that WinPCap obtains the
> timestamp from the system as packets are received; since the system itself
> reflects the correct time, the discrepancy we are seeing strikes me as rather
> odd. Has anyone else seen this or know what could cause it?
> The command line used to start Dumpcap from SrvAny is:
> -i \Device\NPF_{ABF2B612-CEAA-46CE-BEEB-D401F37BAEFF} -B 8 -b filesize:5000
> -b files:5000 -w c:\sniff\BAT.cap
> The version of Wireshark we are using is 1.0.0, with WinPcap 4.0.2. (Yes, I
> know it's old. We can easily update to the latest version, but I figured I'd
> ask anyway in case anyone knows of a different cause for this issue.)
> Thanks,
> -- Phil

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