Wireshark-users: Re: [Wireshark-users] Protocol Identification using Payload Content
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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Mon, 5 May 2008 16:52:35 -0700

On May 5, 2008, at 4:43 PM, Isara Anantavrasilp wrote:


So, you mean that when Wireshark tells me that packet X belongs to
protocol Y, it doesnt use just transportation port?
Correct. There are many protocols that run atop TCP or UDP that aren't assigned to particular ports but that Wireshark needs to identify in packets. 


I suppose I should look at the Wireshark code then.
I hate to ask, but does anyone know where (roughly) these heuristics are? 
I believe they must be stored on some files, right?
The heuristics for a particular dissector are in the source code for that dissector. Look for dissectors whose registration routine calls heur_dissector_add().
The heuristics do *NOT* necessarily just look for a particular "signature". Not all protocols have a simple "signature"; a heuristic might check for packet lengths, the values of various fields, or both.