On VPC-DI, traffic is carried on the DI network between VMs within the VPC-DI instance.
In releases prior to 21.4, VPC-DI VMs did not enforce encryption of traffic received on the DI network. It accepted both encrypted and unencrypted packets.
In Release 21.4, most non-midplane TCP/UDP control packets are now encrypted to better meet overall security objectives.
As a result of this feature enhancement, StarOS upgrades are only supported from 21.3.x to 21.4. Upgrades from any earlier release will not complete successfully. Before upgrading to 21.4, you must upgrade first to Release 21.3.1 or higher.
Downgrade from 21.4 to an earlier release is unaffected by this change.