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Re: Heuristic Dissector Priority
From: Evan Huus <eapache () gmail com>
Date: Mon, 22 Apr 2013 12:22:18 -0400

On Mon, Apr 22, 2013 at 12:11 PM, Richard Maudsley <
richard.maudsley () powwownow com> wrote:

 My plugin registers a UDP heuristic dissector which handles several
protocols multiplexed on the same port. This is working fine, except that
one of the built-in Wireshark dissectors is picking up packets before I get
a chance to see them and blocks my dissector from running, even though I
would be able to return TRUE from the dissector procedure and handle the

If the dissector is incorrectly picking up the packet (ie it thinks it
contains protocol X, but it doesn't) then file a bug against the heuristic
used. If the dissector is correctly picking up the packet (ie the packet
actually contains protocol X) then why does your plugin need to handle it?
Presumably whatever you need to do can be done by improving the existing
dissector or by using a tap.

At first I started looking for some sort of priority setting (a simple
integer precedence on the dissector would have made sense), but it doesn’t
look like such a thing exists. Then I started looking into more complicated
solutions, such as disabling the offending dissector, allowing my dissector
to run, and invoking it afterwards as a sub-dissector.****

I'm a bit confused by this - are you wrapping an existing protocol in some
special header, but the existing heuristic is skipping the header and
jumping straight to the payload?

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