[Snort-users] preprocessors

Jonas Pfoh pfoh at ...14725...
Wed Dec 16 07:56:06 EST 2009


I have a two questions to using preprocessors.

1. Do I understand correctly that preprocessors such as frag3 do some 
preprocessing (in the case of frag3, assemble packets), then send them 
along to the detection engine to be analyzed?  Clearly it makes sense 
that they do as they are called "preprocessors", but it brings me to my 
next question...

2. Preprocessors like sfPortscan, seem to do less preprocessing and more 
  alerting...shouldn't this be the job of the detection engine?  Is it 
done in a preprocessor, because state is needed?  When an alert is 
triggered by the preprocessor, is/are the packet(s) still sent to the 
detection engine?

Thanks for you help.


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