Wireshark-bugs: [Wireshark-bugs] [Bug 8688] Modbus dissector - Info column response and query pr
Comment # 2
on bug 8688
from g2mk
(In reply to comment #1)
> The display of the query/response strings is based on the TCP port number
> (with a default value set to 502).
> It looks like your capture is using port 503 instead.
You are right - port <> 502 is reason of this behavior.
Isn't relaying just on port number (as this example shows) a bit tricky?
MODBUS Messaging on TCP/IP Implementation Guide V1.0b:
The listening TCP port 502 is reserved for MODBUS communications. It is
mandatory to listen by default on that port. However, some markets or
applications might require that another port is dedicated to MODBUS over TCP.
For that reason, it is highly recommended that the clients and the servers give
the possibility to the user to parameterize the MODBUS over TCP port number. It
is important to note that even if another TCP server port is configured for
MODBUS service in certain applications, TCP server port 502 must still be
available in addition to any application specific ports.
> You can change this in
> Edit -> Preferences -> Protocols -> Modbus/TCP.
> After the change, the prefixes are correct and you do not have anymore
> malformed errors.
Is it possible that I (filter) can't find Protocols -> Modbus branch?
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