This week I have been looking at how to detect TCP/IP ports on a local area network to see if an application was setup correctly. And while using ping and tracert from a DOS prompt works well for somethings, I was looking at what else I could use. For Mac OS X users, the Network Utility tool features ping and traceroute options, or you can always use a terminal window directly to ping and traceroute. To verify that you have a listening port, the command line utility netstat -a comes in handy on both Windows and Mac OS X. With this you can verify that a particular port number is listening. You can still use the website CanYouSeeMe.org, if you want to verify that your particular computer is open to the Internet, but this only works if your router is setup to forward requests for this port. In the case where you want to run a VNC or some other service for only local network connections, netstat works much better to verify that the port is in fact listening.

Another tool which Windows users might find handy is Microsoft’s PortQryUI tool. This utility reports the port status of TCP and UDP ports on a computer that you select.