Sometimes they are. It depends on how the capture was generated. If you look in the options of Wireshark there is one to detect bad checksums, so clearly there

Sometimes they are. It depends on how the capture was generated. If you look in the options of Wireshark there is one to detect bad checksums, so clearly there is a way to capture them. Here is one such way: https://stackoverflow.com/questions/22101650/how-can-i-receive-the-wrong-ethernet-frames-and-disable-the-crc-fcs-calcul https://stackoverflow.com/questions/22101650/how-can-i-recei... This can be used to detect partially-bad network cables, because there is no reason you should ever receive a bad FCS.