Topic summary
Ethernet trunk
Extracted from the Wikipedia article Trunking.
VLAN
In the context of Ethernet VLANs, Cisco uses the term Ethernet trunking to mean carrying multiple VLANs through a single network link through the use of a trunking protocol. To allow for multiple VLANs on one link, frames from individual VLANs must be identified. The most common and preferred method, IEEE 802.1Q, adds a tag to the Ethernet frame labeling it as belonging to a certain VLAN. Since 802.1Q is an open standard it can work with equipment from any vendor. Cisco also has a (now deprecated) proprietary trunking protocol called Inter-Switch Link which encapsulates the Ethernet frame with its own container, which labels the frame as belonging to a specific VLAN. 3Com used proprietary Virtual LAN Trunking (VLT) before 802.1Q was defined.