Feedback from Sonos / GTK fails
I was experiencing some issues with my Sonos players. This information I received back from their support team. xClaim, what can you/we do about this?
You contacted us on Twitter about some issues with your Sonos system, which we determined were likely the result of a groupcast error state on the players. This arises from a failure in the access point to update it client devices (such as Sonos) with the latest GTK (Group Temporal Key) information. When a device joins your WiFi, it performs a handshake with the access point (AP) to receive the encryption key it can use to decrypt the messages coming from the AP. This key changes periodically for security reasons and the changes are propagated to associated devices by a frame carrying this information called a beacon frame. If a client device does not receive the most recent GTK it will be unable to decrypt or encrypt broadcast or multicast frames. These are messages sent to multiple devices on the network at once, which we use a lot at Sonos. Restarting the AP will cause a re-authentication and a new handshake to occur, and will solve the groupcast problem temporarily.