What is a Trunk?
You can’t describe VLANs without mentioning trunks. It’s a known fact that You can control and segment network broadcasts with VLAN , VLAN trunking enables the movement of traffic to different parts of the network configured in one 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 S1 and S2, and S1 and S3 are configured (trunk link) to enable traffic coming from VLAN 10, 20 and 30. This network simply could not function without VLAN trunks.
