[Guy Harris <guy@xxxxxxxxxx>]

On Tue, May 28, 2002 at 09:01:26AM +0200, christophe.colin@xxxxxxxxxxxxxxx wrote:
> MAC frames include a field Checksum (4 Bytes),

MAC frames may include a checkums; however, there is no guarantee that
the checksum is supplied to the packet capture mechanisms used by
libpcap/WinPcap, and thus there is no guarantee that a traffic capture
includes the checksum.

> and I can't find how force Ethereal to check this checksum ?

There *is* no way to do that - in fact, Ethereal has no way of knowing
whether a frame in a traffic capture *includes* a checksum, unless
somebody happens to know which capture file formats include checksums
and, if they sometimes include it and sometimes don't, how to determine
whether they include it or not.

Libpcap captures don't include checksums on any platform I know of, so
captures that Ethereal itself does do not include checksums.  Ethereal
cannot do anything to get the checksum - it's at the mercy of the
underlying OS packet capture mechanism that libpcap uses.