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 -- Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe, Freiberger Stra?e 42, 09600 Obersch?na, USt-Id: DE253710583 info at tsht.de Fax +49 3731 74200 Tel +49 3731 74222 Mobil: 0172 8790 741