WinError 10040 when communicating with network-connected PLC

[kristianklein]

When trying to read a symbol from a PLC connected to the local network, I get the following error:

OSError: [WinError 10040] A message sent on a datagram socket was larger than the internal message buffer or some other network limit, or the buffer used to receive a datagram into was smaller than the datagram itself

I am able to read symbols just fine when the PLC is connected directly to my PC with an ethernet cable. I am on a corporate network, so this might have something to do with it?

I tried increasing the PLC response length in adsGetNetIdForPLC() (in pyads_ex.py, line 395) from 395 bytes to 500 bytes. Now it works and it seems that the received packet is 432 bytes.

Windows 10 Python 3.11.2 pyads 3.4.0 TwinCAT 3.1.4024.44

[chrisbeardy]

hello, could you please paste a small reproducible sample bit of code for this? I suspect this is an issue with your network if it works directly. But I can look into it.

[kristianklein]

Thanks, Chris. Here is a bit of code that produces the error:

import pyads

conn = pyads.Connection(ams_net_port=10000, ip_address="10.10.10.10")

with conn:
    state = conn.read_state()
    print(state)

[kryskool]

Hi @kristianklein

have you change the default port ? normally it's 851 (instead of 10000)

Regards,

[kristianklein]

@kryskool, port 10000 is for the system service. My TwinCAT 3 C++ task defaults to port 350, but the issue exists on both ports.

[chrisbeardy]

did this get resolved?