IPID field filtering

["Mcintosh, Fraser" <40121324 () live napier ac uk>]

Good afternoon!


I am a computer security student currently undertaking an Honours project on covert channels and steganography. I tried 
to use Snort to raise an alert if it finds ASCII characters in the IPID field of frames. However, I keep getting an 
error message saying that the value has to be a number when filtering the IPID field. After trying to find a reason as 
to why Snort doesn't allow this I found nothing. Therefore I would be very greatful if someone could offer an 
explanation as to why Snort does not support filtering against strings for the IPID field.


Many thanks, Fraser McIntosh.

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