I've been using the library with an S7-1200 running firmware v4.5.1 in a test lab and have found an issue when use_tls=True is set.

The current python-snap7 main branch (as of 6 May 2026) is TLS wrapping all layers of the protocol (TPKT/COTP/S7CommPlus). Instead TLS should only be applied to the S7CommPlus protocol layer and not TPKT/COTP.

I've validated that only S7CommPlus should be TLS wrapped by examining the behavior of the implementation here: https://github.com/thomas-v2/S7CommPlusDriver.

Captures attached:

• S7CommPlusDriver_CS_S7-1200_10p1p128p6_test - using the library from here: https://github.com/thomas-v2/S7CommPlusDriver
• Snap7_Python_S7-1200_10p1p128p6_test - using the latest main branch of python-snap7

S7-1200_10p1p128p6_test.zip

Let me know if there is anything else I can do to assist in testing and/or debugging. At the moment I have access to:

• S7-1200 (6ES7 212-1BE40-0XB0 - running v4.5.1)
• S7-1500 (6ES7 511-1AK02-0AB0 - running v2.9.4)