Sending commands via ethernet to PLC


I’d like to use an arduino board to connect buttons to a PLC via ethernet. It needs to send the button state or change of state.
In the PLC I can receive TCP or UDP packets.

I need to send only 1 or 2 bytes at a time.

Could someone please help me on how to send very little information via ethernet fast and reliable to the PLC?
Is it better to use UDP or TCP packets?

Is there anywhere a tutorial on how to send plain packets? I couldn’t find one.