title: UDP how to recvfrom different ports at server side with binded port
body: <p>I have a problem on UDP socket port bind on receiving message from different client ports.
  I am compiling a C++ utility to check (20K) ports of a Linux server.
  I create client threads to send different ports of server by pthread_create.
  At server side, I have to bind socket to certain port, so it can only recvfrom (select like blocked IO)only 1 port.
  Can you give me some suggestions on UDP server to receive message from different ports?</p>