Actually you can’t ping a specific port by using the ping command to test whether specified port is open or not. The ping command is used to test specified node/host whether it is live or not. It uses ICMP packets (wiki.answers.com).

You can test a port whether it is live or not by telneting the port using the telnet command. The telnet command is a utility to connect over TCP and defaults to port 25 23 (make a TCP connection to port 25 23 on remote computer/server). But if you specify a different port than 25 23, then what the telnet command do is opening a TCP connection on the specified port to the remote computer/server.

For example (in Windows):

C:\> telnet 192.168.1.1 80

In above example, the telnet command is trying to open HTTP connection (port 80) to the 192.168.1.1 host computer rather than opening the default telnet port (port 25 23).

If the above connection is unsuccessful, then you will get this message:

C:\>telnet 192.168.1.1 80
Connecting To 192.168.1.1...Could not open connection to the host, on port 80: Connect failed

Otherwise, you will prompted to enter another input/arguments for a service of the specified port.

If you dealing with firewall, typically it blocks TCP/UDP connection in a direction or both direction on specified port. So firewall didn’t deal with “telnet protocol” rather than TCP/UDP connections on specified ports.

For example, a firewall on destination host is blocking TCP connection on port 25 23 (the default telnet protocol port) and not for the other ports. You are telnetting on port 80, your telnet command will be successful, and you will also knew that TCP port 80 on destination host is open.