Symptom

Using Nexus 9000 parent switches with Nexus 2000 switches attached. adding the command `switchport trunk allowed vlan x add` to an fex trunk port can remove the already configured VLANs.

Conditions

Nexus 9000 and Nexus 2k trunk ports

Workaround

re-add the removed VLANs via the Allowed CLI with all VLANS needed included.

Further Problem Description