Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 12484] New: Please implement MODBUS/UDP dissector

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Bug ID	12484
Summary	Please implement MODBUS/UDP dissector
Product	Wireshark
Version	2.0.3
Hardware	x86-64
OS	Windows 7
Status	UNCONFIRMED
Severity	Enhancement
Priority	Low
Component	Dissection engine (libwireshark)
Assignee	bugzilla-admin@wireshark.org
Reporter	aidasan@hotmail.fr

Build Information:
Version 2.0.3 (v2.0.3-0-geed34f0 from master-2.0)

Copyright 1998-2016 Gerald Combs <gerald@wireshark.org> and contributors.
License GPLv2+: GNU GPL version 2 or later
<http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (64-bit) with Qt 5.3.2, with WinPcap (4_1_3), with libz 1.2.8, with
GLib 2.42.0, with SMI 0.4.8, with c-ares 1.9.1, with Lua 5.2, with GnuTLS
3.2.15, with Gcrypt 1.6.2, with MIT Kerberos, with GeoIP, with QtMultimedia,
with AirPcap.

Running on 64-bit Windows 7 Service Pack 1, build 7601, with locale C, with
WinPcap version 4.1.3 (packet.dll version 4.1.0.2980), based on libpcap version
1.0 branch 1_0_rel0b (20091008), with GnuTLS 3.2.15, with Gcrypt 1.6.2, without
AirPcap.
       Intel(R) Core(TM) i5-3337U CPU @ 1.80GHz (with SSE4.2), with 3974MB of
physical memory.


Built using Microsoft Visual C++ 12.0 build 40629
--
Hello,
I am from the automation world. We are using a lot of system with MODBUS/UDP
instead of MODBUS/TCP.

The main reason is speed, less load on the network, multicast possible.

I don't really understand why the dissector of the MODBUS/UDP has been drop.

Here are the build with the MODBUS/UPD dissector:
 - 1.6.4 Portable
 - 1.8.14 Portable

I know MODBUS/UPD is not in the MODBUS specification but if you look on the
MODBUS official web page under the "technical resources", there is some source
code for MODBUS/UDP.

http://www.modbus.org/tech.php

Also if you go to the IEEEA website and look which port is registered (page
10):
http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?&page=10

you will find:
mbap    502    tcp    Modbus Application Protocol    [modbus.org]   
[Dennis_Dube]        2014-06-10                
mbap    502    udp    Modbus Application Protocol    [modbus.org]   
[Dennis_Dube]        2014-06-10    

If the MODBUS association has registered the UPD port 502 it is quite official
and standard.


Ps here is a quote from a Digi Int'l (www.digi.com) member:
====================================================
Actually, from an application sense, Modbus/UDP is just as reliable as
Modbus/TCP. Think of the transaction:
A master sends a Modbus/UDP poll:
 - if the slave gets the poll, it returns a Modbus/UDP response
 - if the Master receives the response, the poll/response is complete.
 - if the master does NOT receive the response, it's a time-out. Just try poll
again
 - if the slave doesn't get poll, there is no response, it's a time-out. Just
try poll again
 - in all cases, the slave doesn't really care if the master saw the response.
 - in all cases, decades of Modbus/RTU have created masters capable of timeout
& retry. 

Modbus/UDP is just like that.
====================================================

Thank you for your understanding and I hope the dissector will be updated.

Best regards
Christophe.

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