A trunk port carries packets on one or more specified VLANs. Packet that ingress on a trunk port are in the VLAN specified in its 802.1Q header, or native VLAN if the packet has no 802.1Q header. A packet that egresses through a trunk port will have an 802.1Q header if it has a nonzero VLAN ID. Any packet that ingresses on a trunk port tagged with a VLAN that the port does not trunk is dropped.
(switch(config-if)#) Configure an interface as a trunk port:
switchport mode trunk
(switch(config-if)#) Add the allowed VLANs:
switchport trunk allowed vlan add 1,50,100
(switch(config-if)#) Assign a native VLAN:
switchport trunk native vlan-id 1
(switch#)
show interfaces switchport