If a WAN Edge image version is newer than the controller's version, what happens when attempting the upgrade?

Cisco SD-WAN best practices dictate that controllers (vManage, vSmart, vBond) should always run a software version equal to or newer than the WAN Edge devices they manage. When attempting to upgrade a WAN Edge device to a version newer than the controller, the upgrade process will fail. This is a deliberate design to prevent potential compatibility issues and ensure proper control plane and data plane functionality. A warning message will be displayed, indicating that the controller must be upgraded first. The upgrade button would not be greyed out, as the system allows the attempt but prevents the incompatible action. Proceeding with a warning or no warning would violate the versioning best practices and lead to an unstable network.