TCP port diagnostics

Audience: technicians with existing networking experience

Overview: identify network problems with a service or TCP/UDP port on a remote server, or client/server connection between 2 networks. We will use Windows tools such such as PortQryUI.exe, JPerf (Iperf), and TraceTCP.exe to (1) confirm is a service is listening on a remote port, (2) load test network between client & server on a specific port, and (3) identify which node along the route may be dropping or throttling traffic destined for a specific port

Downloading the tools used in this article

• PortQryUI.exe
  • Microsoft direct download page https://www.microsoft.com/en-gb/download/details.aspx?id=24009
  • Copy attached at end of this article (v1.0 23-Oct-2019)
• Jperf
  • Requires Java: https://www.java.com/en/download/
    • Copy of installer attached at end of this article (v8.241 14-Jan-2020)
  • Direct download from SourceForge https://sourceforge.net/projects/iperf/files/jperf/jperf%202.0.0/jperf-2.0.0.zip/download 
  • Copy attached at end of this article (v2.0 219-Mar-2008)
• TraceTCP.exe
  • Requires WinPcap
    • Direct download page https://www.winpcap.org/install/
    • Copy of installer attached at end of this article (v4.3.1 1-Mar-2013)
  • Direct download from GitHub project https://github.com/0xcafed00d/tracetcp/releases
  • Copy attached at end of this article (v1.0.3 25-Nov-2016)
  • Full documentation: https://github.com/simulatedsimian/tracetcp

PortQryUI.exe

Launch PortQryUI.exe (it's a GUI front end for the command line tool PortQry.exe). Enter the destination IP or hostname (the server hosting the service). Specify the port to query and the protocol (TCP or UDP). Click Query button. The tool will report if a service is listening on that port, using that protocol, on that IP or hostname.

Jperf

You'll need at least 2 machines, 1 in server role (listening) and 1 as the client. The "server" can be a standard Windows desktop machine. Jperf implements Java, so it must already be installed. Launch jperf.bat and set up the server by selecting "Server", specify a listening port, and click the start button. We don't intend offend, but ensure the following obvious scenario:

• Server firewall and gateway firewall ALLOW inbound traffic on that port and protocol
• No competing service is already running on this server

With the "server" now listening, run Jperf.bat on the client and click start to begin streaming data over to the server, where it will graph and log the results.

TraceTCP.exe

This tool requires WinPcap installed in order to capture the TCP packets. You'll need to run this tool from the command line. Launch cmd.exe and navigate to the folder where tracetcp.exe exists. This tool is similar to the Windows tracert command. Syntax: tracetcp {hostname or ip}:{port} 

Example: 

tracetcp server.domain.com:1234
...or...
tracetcp 11.22.33.44:1234