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.
Configure an interface as a trunk port:
switchport mode trunk
Add the allowed VLANs:
switch(config-if)#switchport trunk allowed vlan add 1,50,100
Assign a native VLAN:
switchport trunk native vlan-id 1
Show commands to validate functionality:
show interfaces switchport