Original config with a string of allowed vlans that goes over a single line. ! original config: conf t interface GigabitEthernet0/22 description test uplink 1 switchport access vlan 3 switchport trunk encapsulation dot1q switchport trunk native vlan 2 switchport trunk allowed vlan 3,100,101,150,250,350,500,550-555,800,902-904 switchport trunk allowed vlan add 950 switchport mode trunk logging event trunk-status carrier-delay msec 0 no keepalive channel-group 3 mode active end If we want to add an additional set of vlans (in this case 801-803, we collect all the allowed vlans and put them into one string, and re-enter that: conf t interface GigabitEthernet0/22 switchport trunk allowed vlan 3,100,101,150,250,350,500,550-555,800-803,902-904,950 end Then if we look at the interfaces new config, we see the additional vlans allowed over the interface: netlab-sw2#sh run int g0/22 Building configuration... Current configuration : 396 bytes ! interface GigabitEthernet0/22 description test uplink 1 switchport access vlan 3 switchport trunk encapsulation dot1q switchport trunk native vlan 2 switchport trunk allowed vlan 3,100,101,150,250,350,500,550-555,800-803 switchport trunk allowed vlan add 902-904,950 switchport mode trunk logging event trunk-status carrier-delay msec 0 no keepalive channel-group 3 mode active end netlab-sw2# |