IP related question..

[Holm Tiffe]

Hi all,

I want to use some cheap chinese TTL-RS232 to Ethernet modules
(USR-TCP232-T2) from usriot.com.

I've configured them as a TCP server on port 2323 on a local network.
The RS232 side is connected to an embeded micro that currently connects
to my FreeBSD 11.1-RELEASE-p6 development machine with an terminal
program over USB.

This way I can telnet into Port 2323 on the USR module and the entered
input arrives on the serial line in the terminal emulator..so far so
good, but interesting things do happen if I reset the USR Module with an
still open telnet session and enter some text there, the USR module
answers with an connection reset, think that's ok. But why the heck
the FreeBSD host is now sending an zero window packet?
...this zero window packes gets answered with an connection reset from
the module..which gets answered with an zero window packet form the host
...which gets answered... I think you understand my problem.

There are other possibilities to trigger this tcpip war it seems,
here is a wireshark dump where you can see what happens.

https://www.tsht.de/files/3-dump.pcapng.gz


I must find a way to prevent this tcpip pingpong to happen.
The chinese USR People have made a new firmware version for the modules
already which works better then the previous one but I have problems
to explain hy those zero windows are sent from FreeBSD.. can someone
 help please?

Regards,

Holm

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