One-click network diagnostics
Server located at in Vallensbaek, DK  
  Documentation | Results Summary | About NPAD  

NPAD (Network Path and Application Diagnosis) is designed to diagnose network performance problems in your end-system (the machine your browser is running on) or the network between it and your nearest NPAD server. For each diagnosed problem, the server prescribes corrective actions with instructions suitable for non-experts.

Brief instructions

  • The test results are most accurate over a short network path. If this NPAD server (located at Vallensbaek, DK) is not near you, look for a closer server from the list of Current NPAD Diagnostic Servers.
  • Have an end-to-end application performance goal (target round-trip time and target data rate) in mind. Enter the parameters on the form below and click Start Test. Messages will appear in the log window as the test runs, followed by a diagnostic report.
  • In the diagnostic report, failed tests (in red) indicate problems that will prevent the application from meeting the end-to-end performance goal. For each message, a question-mark link ([?]) leads to additional detailed information about the results.
  • Every test is fully logged (including your IP address) and test results are public. We use the logs and results to further refine the software.
For more information, see the NPAD Documentation, especially the sections:

Note that tests take 2-5 minutes, depending on the parameters that you provide and the network path. If there is a queue, waiting times might be long.

Please send comments and suggestions about the server to Jan Olsson <jan at olsson dot net>.

Command line client

If the Java applet above exhibits errors or the form is blank, try the command line diagnostic client. Download it (diag-client.c) and compile it:

cc diag-client.c -o diag-client

Run it:

./diag-client <server_name> <port> <target_RTT> <target_data_rate>

Where server_name is the hostname of a diagnostic server (e.g., this server), and port is the port number the diagnostic service runs on (8001 for this server).

About NPAD

This software (NPAD/pathdiag version 1.5.6) is being developed under a collaboration between the Pittsburgh Supercomputer Center (PSC) and the National Center for Atmospheric Research (NCAR), funded under NSF grant ANI-0334061. The project is focused on using Web100 and other methods to extend fairly standard diagnostic techniques to compensate for "symptom scaling" that leads to false positive diagnostic results on short paths. It is still experimental software and may have bugs. Please help us improve this service by providing feedback about the results. Send suggestions, comments and questions to

Matt Mathis and John Heffner, Pittsburgh Supercomputing Center, 2005.