Do not use this to scan modbus tcp port 502


As shown in the figure, we can see that there is only TCP handshake but no TCP waving process when scanning the port.

In our project, PLC or dedicated communication card provides modbus tcp interface, using port 502, but this communication card is relatively weak, supporting up to 4 tcp connections, and will not automatically clean up tcp connections that have not ended normally. So after scanning with this tool several times, all network cards will become unusable.

I used this command to scan the LAN several times a few weeks ago. The final result was that we manually plugged and unplugged the network cables of the network cards in 288 containers one by one before we restored the network. It took 4 people 3 days to work.


Test with the tnc command that comes with powershell, and you can see that there is a complete tcp handshake and wave process, so there will be no such problem. But the tnc command is very slow, and I am also looking for a better tool.