There is a Global ACI option (SYSTEM > SYSTEM SETTINGS >> Fabric Wide Setting | Enforce Domain Validation) that forces ACI to check that an EPG is linked to a Domain. The Cisco Application Centric Infrastructure Design Guide White Paper recommends that this option be turned on, but it is a once-only option. Once it is turned on, you can't turn it off.
And that includes turning it off by restoring a snapshot that was taken before the option was turned on.
So the point of this post is to warn anyone who turns this option on (and I recommend that you do), you should do so as the very first configuration action you take with a new Fabric, BEFORE you take any snapshots.
If you try to restore a snopshot taken before the option was enabled you will receive the following error:
Failed to apply tree: Asking for domain validation is a one time operation. No further changes allowed
1. According to bug#CSCvs40360 and release notes, v4.2(6d) should support AES-256 for SNMPv3 encryption. But when I try to add SNMP User profile (screenshot), I still only have AES-128 or DES or None... OR maybe I need to specifically enabling it somewher...