PortqryUI is GUI interface for portqry command line utility.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.
Depending on the process that listens on a UDP port, sometimes it may be difficult to determine the status of that UDP port. When an unformatted zero-length or fixed-length message is sent to a target UDP port, the port may or may not respond. If the port responds, it has a status of LISTENING. If you receive an ICMP “Destination unreachable” message from a UDP port, or if a TCP reset response is returned from a TCP port, the port has a status of NOT LISTENING. Typical port scanning tools report that the port has a LISTENING status if the target UDP port does not return an ICMP “Destination unreachable” message. This result may not be accurate for one or both of the following reasons:
• When there is no response to a directed datagram, the target port may be FILTERED.
• Most services do not respond to an unformatted user datagram that is sent to them.
Typically, only one correctly formatted message that uses the session layer or that uses the application layer protocol that the listening service or the program understands elicits a response from the target port.
When you troubleshoot a connectivity problem, especially in an environment that contains one or more firewalls, it is useful to know if a port is being filtered or if it is listening. PortQry includes some special features to help make this determination on selected ports. If there is no response from a target UDP port, PortQry reports that the port is LISTENING or FILTERED. PortQry then sends a correctly formatted message that the listening service or program understands. PortQry uses the correct session layer or application layer protocol to determine if the port is listening. PortQry uses the Services file that is located in the %SYSTEMROOT%\System32\Drivers\Etc folder to determine which service listens on each port.
Note This file is stored on each Microsoft Windows Server 2003, Windows XP, and Windows 2000-based computer.
Because PortQry is intended as a troubleshooting tool, it is expected that users who use it to troubleshoot a particular problem have sufficient knowledge of their computing environment. PortQry version 2.0 supports the following session layer and application layer protocols:
• Lightweight Directory Access Protocol (LDAP)
• Remote Procedure Calls (RPC)
• Domain Name System (DNS)
• NetBIOS Name Service
• Simple Network Management Protocol (SNMP)
• Internet Security and Acceleration Server (ISA)
• SQL Server 2000 Named Instances
• Trivial File Transfer Protocol (TFTP)
• Layer Two Tunneling Protocol (L2TP)
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