[Winpcap-users] Using WinPcap "breaks" TCP

[Marc Rennhard]

Dear all,

I'm having a strange problem that I believe is related to WinPcap because it
only happens with the two WinPcap-based applications I use (Wireshark and
Cain).

I use the latest Wireshark and Cain versions with Winpcap 4.0.1 under
Windows XP with all latest patches and drivers. The problem occurs on both
my Laptops, a Thinkpad T40p and a T60. It happens with both the wired and
wireless interfaces. The problem did not happen until a few weeks ago,
though I cannot tell exactly when it started or what (e.g. software
upgrades) may have been the cause.

The symtomps are as follows: without running Wireshark/Cain, networking
works fine. When starting Wireshark or Cain, it still works. When starting
sniffing, TCP-based applications no longer work. With Wireshark, I can see
that the 3-way handshake is recorded (so handshaking seems to work), but no
data is exchanged afterwards and the TCP connection "hangs". Other protocols
still seem to work, e.g. name resolutions (UDP-based) work flawlessly. Even
after terminating Wireshark or Cain, TCP remains "broken" and only rebooting
helps.

Does anyone have an idea what the reason for this problem may be?

Thanks for any help,
Marc
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