Wireshark · Ethereal-dev: Re: [Ethereal-dev] Problem detecting 802.11b frames with CRC errors

[Guy Harris <gharris@xxxxxxxxx>]

Guy Harris wrote:

> For Ethernet packets in Windows Sniffer, it appears that there is a bit 
> in the per-packet header before the packet data that indicates whether 
> the CRC is correct; Ethereal doesn't currently use that bit - at some 
> point we'll probably change the API exported by the capture-file-reading 
> library in Ethereal to let Ethereal get that information, and have 
> Ethereal display it.  The significance of that bit was determined by 
> seeing which packets contained a CRC that wasn't valid; not having seen 
> any 802.11 captures with a CRC, a similar check couldn't be done.  Now 
> that you've supplied a capture with frames known to have bad CRCs (and 
> with the other frames assumed to have good CRCs), we can test whether 
> the same bit, or perhaps a different bit, indicates whether the CRC of 
> an 802.11 frame is good or bad, so that, when we change the API in 
> question, we might be able to supply that flag for 802.11 Windows 
> Sniffer captures as well.

It appears that the same bit indicates a bad CRC in 802.11 captures; 
I've put a comment to that effect in the code to read NetXRay and 
Windows Sniffer files, for future reference if, as, and when code to use 
that bit is added.