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Re: Wireshark Dissector
From: suraj mukade <surajmukade () gmail com>
Date: Wed, 26 Jun 2013 09:53:52 +0530

Hi Harris,
Thanks for the precise answer. I understood thing dissector_add_uint();
But I am not clear with dissector table concept.
Let me explain, My Ethernet frame will have some Ethernet type value (for
example "ABCD")which wireshark doesn’t understand.
So if the frame with Ethernet type value="ABCD" comes how wireshark will
know that it has to call my dissector?
What is the way to register that value.

Sorry if I am wrong I am trying to analog it with the call
dissector_add("udp.port", global_foo_port, foo_handle);
where we are requesting Wireshark to call foo_handle on receiving packet on
UDP port global_foo_port.

In short is it not sufficient to do similar call as in case of UDP?




On Wed, Jun 26, 2013 at 6:37 AM, Guy Harris <guy () alum mit edu> wrote:


On Jun 25, 2013, at 12:31 AM, suraj mukade <surajmukade () gmail com> wrote:

How to call your own dissector based on type field in Ethernet? After
getting Type value from Ethernet frame,I want to dissect the custom
Ethernet frame with some added fields and then proceed the normal
dissection.

The answer to your question depends on how your protocol works.

If the data in a packet using your protocol looks something like:

        Ethernet destination
        Ethernet source
        The type field value you've registered with the IEEE for your
protocol
        Fields for your protocol, including something to indicate what
protocol comes after it
        Those protocols

then you would have your dissector do

         dissector_add_uint("ethertype", {your ethertype value}, {a handle
for your dissector});

where {your ethertype value} is the Ethernet type value registered for
your protocol and {a handle for your dissector} is, well, a handle for your
dissector, created with, for example, register_dissector() or
new_register_dissector() or create_dissector_handle() or
new_create_dissector_handle().

Your dissector would then either define a dissector table for the field
that indicates what protocol comes after (and you'd have to change other
dissectors to register in that table) or, if the field is a protocol type
field that already exists, such as an Ethernet type value, you could just
do something such as

        ethertype_dissector_table = find_dissector_table("ethertype");

in your reg_handoff routine and then call dissector_try_uint() with the
Ethernet type field's value when it's time to dissect the payload.
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-- 
Thank You,



"The only thing in the world we need to fear is fear itself"
Suraj Mukade,
Scientific Officer,
Bhabha Atomic Research Center, Mumbai.
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