What is a VLAN Trunk?
You can’t describe VLANs without mentioning trunks. It’s a known fact that you can control and segment network broadcasts with VLANs. VLAN trunking enables the movement of traffic to different parts of the network configured as a VLAN.
A trunk is a point-to-point link between two network devices that carries more than one VLAN. With VLAN trunking, you can extend your configured VLAN across the entire network. Most Cisco switches supports the IEEE 802.1Q used to coordinate trunks on FastEthernet and GigabitEthernet.
In the figure above, the links between switches SW1 and SW2, SW1 and SW3 are configured as trunk links to enable traffic between VLAN 10, 20 and 30. This network simply could not function without VLAN trunks.