Switch1(config)# interface g1/0/20
Switch1(config-if)# switchport trunk encapsulation dot1q
Switch1(config-if)# switchport mode trunk
Switch1(config-if)# switchport trunk allowed vlan 100,200
—
Switch2(config)# interface g1/0/20
Switch2(config-if)# switchport trunk encapsulation dot1q
Switch2(config-if)# switchport mode trunk
Switch2(config-if)# switchport trunk allowed vlan 100,200