Wireshark · Wireshark-dev: [Wireshark-dev] Question about port registrations

["Bryant Eastham" <beastham@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

All-

 

We had a user complain about one of our (private) dissectors not working. I wanted to verify my understanding of what we see…

 

In my plugin registration I use:

 

dissector_add(“tcp.port”, EPS_PORT, eps_handle);

 

EPS_PORT is our registered port, 3567.

 

The reported behavior is that a TCP session from port 2424 -> 3567 was not using our dissector. As it turns out, 2424 is registered to TPNCP in packet-tpncp.c. This leads me to questions about the prioritization given to different dissectors. Could someone in the know enlighten me?

 

Q: Does “dissector_add” differentiate between src and dst port? [I think not, the registration is by name and the dissector (TCP) chooses how to use it.]

 

Q: Does wireshark prioritize between built-in vs. plugin dissectors? [I think not.]

 

Q: Does wireshark prioritize between dissectors based on matches on src vs. dst port?

 

My fundamental issue is that I would expect that priority be given to the dissector on the *server* (dst) port, as it is the more likely to be standardized vs. ephemeral.

 

As a sanity check, disabling the TPNCP protocol and reloading the trace file correctly uses my dissector for the traffic in question.

 

Thanks for your answers…

 

-Bryant

 

	Panasonic Electric Works Laboratory of America - SLC Lab 4525 So. Wasatch Blvd., Suite 100, 84124 Salt Lake City, UT 84124
	T 801.993.7124 F 801.993.7269 beastham@xxxxxxxxxxxxxxxxxxxxxxxxxx	Bryant Eastham Chief Architect