PortQry is a command-line utility that you can use to help troubleshoot TCP/IP connectivity issues. This utility reports the port status of target TCP and User Datagram Protocol (UDP) ports on a local computer or on a remote computer. PortQry version 2.0 also provides detailed information about the local computer's port usage. PortQry version 2.0 runs on all the following operating systems:
- Microsoft Windows Server 2003
- Microsoft Windows XP
- Microsoft Windows 2000
PortQry reports the status of a port in one of the following ways:
- LISTENING This response indicates that a process is listening on the target port. PortQry received a response from the target port.
- NOT LISTENING This response indicates that no process is listening on the target port. PortQry received one of the following Internet Control Message Protocol (ICMP) messages from the target port:
- Destination unreachable
- Port unreachable
- FILTERED This response indicates that the target port is being filtered. PortQry did not receive a response from the target port. A process may or may not be listening on the target port. By default, PortQry queries a TCP port three times before it returns a response of FILTERED and queries a UDP port one time before it returns a response of FILTERED.
http://support.microsoft.com/default.aspx?kbid=832919