Command
Switchport Trunk Encapsulation dot1q
Use
Enables dot1q trunking encapsulation on the interface.
Syntax
Switch(config-if)#switchport trunk encapsulation dot1q
Example
First, here is the trunking information for SW3. Note fa0/19, which is set to ISL.
SW3(config-if)#do show int trunkPort Mode Encapsulation Status Native vlan Fa0/19 auto isl trunking 1 Fa0/20 auto n-802.1q trunking 1 Fa0/21 auto n-802.1q trunking 1 Fa0/22 auto n-802.1q trunking 1 Port Vlans allowed on trunk Fa0/19 1-4094 Fa0/20 1-4094 Fa0/21 1-4094 Fa0/22 1-4094 Port Vlans allowed and active in management domain Fa0/19 1,10-20,55,99,555 Fa0/20 1,10-20,55,99,555 Fa0/21 1,10-20,55,99,555 Fa0/22 1,10-20,55,99,555 Port Vlans in spanning tree forwarding state and not pruned Fa0/19 none Fa0/20 none Fa0/21 1,10-11 Fa0/22 none SW3(config-if)#
Next, dot1q trunking is enabled on fa0/2 on SW3.
SW3(config)#int fa0/2 SW3(config-if)#switchport trunk encapsulation dot1q
Here is the trunking information after making the changes.
SW3(config-if)#do show int trunkPort Mode Encapsulation Status Native vlan Fa0/19 auto 802.1q trunking 1 Fa0/20 auto n-802.1q trunking 1 Fa0/21 auto n-802.1q trunking 1 Fa0/22 auto n-802.1q trunking 1 Port Vlans allowed on trunk Fa0/19 1-4094 Fa0/20 1-4094 Fa0/21 1-4094 Fa0/22 1-4094 Port Vlans allowed and active in management domain Fa0/19 1,10-20,55,99,555 Fa0/20 03:12:24: %LINEPROTO-5-UPDOWN: Line1,10-20,55,99,555 Fa0/21 1,10-20,55,99,555 Fa0/22 1,10-20,55,99,555 Port Vlans in spanning tree forwarding state and not pruned Fa0/19 none Fa0/20 none Fa0/21 1,10-11 protocol on Interface FastEthernet0/19, changed state to up Port Vlans in spanning tree forwarding state and not pruned Fa0/22 none