D-Link DES-3010GA - switchport forbidden vlan

D-Link DES-3010FA/GA CLI Reference Guide
Page 303
switchport general acceptable-frame-type tagged-only
The switchport general acceptable-frame-type tagged-only Interface Configuration mode command discards
untagged frames at ingress. To return to the default configuration, use the no form of this command.
Syntax
switchport general acceptable-frame-type tagged-only
no switchport general acceptable-frame-type tagged-only
Default Configuration
All frame types are accepted at ingress.
Command Mode
Interface Configuration (Ethernet, port-channel) mode
User Guidelines
There are no user guidelines for this command.
Example
The following example configures Ethernet port 6 to discard untagged frames at ingress.
Console(config)# interface ethernet 6
Console(config-if)# switchport general acceptable-frame-type tagged-only