Troubleshooting Kaltura Building Block for Blackboard - Slow Performance

Slow performance of the Kaltura Video Building Block for Blackboard may be caused by specific types of DNS queries (NBNS queries) that are sent by the network before issuing an HTTP request, and by a specific network setup that can cause a delay in performance.

To troubleshoot the issue, the customer should set a specific IP for Kaltura's hostname in the Blackboard server's hosts file (to override any DNS network), and see if the page load response time is not delayed.

To set a specific IP for Kaltura's hostname in the Blackboard server's hosts file

  1. Go to the “host” file:  C:windowssystem32driversetc or %systemroot%system32driversetc
  2. Launch notepad with elevated privileges.
  3. In notepad, right-click and select “Run as Administrator“.
  4. Open the host file from the File menu, edit the hosts file so it points to: and to the specific IP  that will override the DNS  entirely. 
  5. Save the file.

If the issue is resolved after changing the host file, the customer should continue investigating what in his network setup may have caused the DNS resolution to slow down the DNS resolution between the Blackboard server and Kaltura server.

We found that NBNS queries that failed were causing the DNS resolution slow down and were not related on the Kaltura end. After changing the network configuration and disabling the NBNS queries, the response time from Kaltura was back to normal.

Note that there could be multiple network configuration issues that might cause the DNS resolution to slowdown and thus we recommend customers to disucss this with their IT department for further troubleshooting

If changing the host file does not resolve the issue, please request from the customer to provide Kaltura Partner Support with a wireshark capture from the Blackboard server while reproducing the slow performance’s issue.

You can download wireshark here.





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