Trunk Mode Command

command: switchport trunk allowed vlan {add | all | except | remove} vlan-list.  This provides a way to easilly add and remove VLANs from the list.  The all option means all VLANs, so you can use it to reset the switch to its original VLAN config of allowing 1-4094.  Except adds all VLANs to the list that aren’t listed, ie: switchport trunk allowed vlan except 100-200.