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#) Configure an interface as a trunk port:
vlan trunk allowed VLANS
(switch#)
show vlan [VLAN-ID]
Example output:
vlan 10
no shutdown
exit
vlan 20
no shutdown
exit
interface 1/1/1
no shutdown
no routing
vlan trunk native 10
vlan trunk allowed 10,20
end