> On Jul 6, 2015, at 3:12 AM, Guy Harris <g...@alum.mit.edu> wrote:
> 
> The use case for some but not other underlying protocols would appear to be 
> "traffic atop protocol X is rarely if ever mis-identified as being for 
> protocol Z, so leave the heuristic on, but traffic atop protocol Y is often 
> mis-identified as being for protocol Z, so turn the heuristic off".  Would 
> that be better handled by, for example, a UI to allow the user to specify the 
> order in which heuristic checks are done, or something such  as that (and a 
> command-line option to do the same, so that this same functionality is 
> available in TShark)?

I had actually been thinking that someday we might indeed offer the ability to 
control the ordering of heuristic dissectors.  I don’t think we need it now, as 
people seem ok with just disabling a heuristic and there aren’t that many.

There is, I think, a reasonable use-case for disabling a heuristic but keeping 
the main protocol enabled. 

One example is RTP, which is extremely "correct" for its "main" protocol 
because it’s setup by SIP/H.323/etc., but is often "incorrect" when enabled as 
a heuristic, either over raw UDP or in TURN messages. (it matches too 
frequently)  Another example is TFTP, which is reasonably correct when its main 
dissector hooks into port 69, but is badly inaccurate when its heuristic is 
used over TURN.

I mention those two because at my previous job I had to deal with captures of 
them, and the gerrit changes 9489 and 9490 to add a preference to disable the 
TFTP heuristic, and disable RTP over TURN, were what triggered Michael 
suggesting we make the enabling/disabling of heuristics a general feature.

-hadriel

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