Does anyone have an example UDP server?

Does anyone have an example UDP server?

Hi All!
I am trying to communicate NB-IoT with UDP (CoAP).
Currently, TagoIO provides examples of TCP/IP, but I can't find UDP at all.
Can I get an example related to UDP Server(middleware)?
I'm new to developer, so I don't know much about it, so I need help me. 
I hope you will answer my question. Thank you.