Fehler gefunden:
If the packets that have incorrect TCP checksums are all being sent by the machine on which Ethereal is running, this is probably because the network interface on which you're capturing does TCP checksum offloading. That means that the TCP checksum is added to the packet by the network interface, not by the OS's TCP/IP stack; when capturing on an interface, packets being sent by the host on which you're capturing are directly handed to the capture interface by the OS, which means that they are handed to the capture interface without a TCP checksum being added to them.
The only way to prevent this from happening would be to disable TCP checksum offloading, but
1. that might not even be possible on some OSes;
2. that could reduce networking performance significantly.
However, you can disable the check that Ethereal does of the TCP checksum, so that it won't report any packets as having TCP checksum errors, and so that it won't refuse to do TCP reassembly due to a packet having an incorrect TCP checksum. That can be set as an Ethereal preference by selecting Preferences from the Edit menu, opening up the Protocols list in the left-hand pane of the Preferences dialog box, selecting TCP, from that list, turning off the Check the validity of the TCP checksum when possible option, clicking Save if you want to save that setting in your preference file, and clicking OK.
