title: How to detect which ports are not blocked in a local network
body: <p>I am trying to run tomcat in local network, I want to run a web service that can be visited by other computers in the same network. It was successful when I use wireless router to form a local network at home. But when I use school's wireless network, web service can't be visited by other computers. I suspect port 80 was blocked, so I try other ports, it doesn't either. </p>
  
  <p>Is there any way to detect which ports are not blocked in the local network?</p>