Issue:
When students take Star tests on Chromebooks, they may experience a white page trying to start the test, or a spinning icon or blank page between questions.
Note: Although this behavior has been identified when accessing Renaissance web-based software and also affects Pearson Education software and Kahoot! software as well as others, it is not universal. We have many customers with wide Chromebook utilization who are not experiencing these issues.
Reason:
After extensive investigation with Google, the most likely cause has been identified as improper handling of wrapped-sequence TCP packets. TCP network communications combine a timestamp value and a random sequence number and store it in a packet's header as 4 bytes. Periodically, the TSVal can exceed the maximum value that can be stored in 4 bytes, causing a roll-over of the TSVal. Some Chromebook models have a TSVal that starts at a very high value, close to the rollover value. When these Chromebooks are used on a network affected by the wrapped sequencing issue, a network device can begin to drop packets as out of sequence when the timestamp rolls over. This rollover can happen as soon as three to five minutes after the Chromebook starts up. This may result in blank or white screens and other issues, depending on what software is being used and where the user is working in the software. In our research specific to Cisco ASA firewall devices, it was determined that a bug (CSCui80835 and CSCuq80704) affects 5500-X Series Firewall devices and could result in the issue described in this article. Please note that other brands of network devices could likewise be affected.
Resolution:
Determine if there's a rule in your network device that is causing rolled-over TSVal timestamp values to be disregarded as out of sequence (also see this reference to the PAWS mechanism: http://www.freesoft.org/CIE/RFC/1323/16.htm). If you are using a Cisco ASA hardware device, obtain the serial number of your device and contact Cisco directly to find out if your device is affected by the bug listed above.