Multiple VLANs are supported between switches through the use of
VLAN trunks. A trunk is a Layer 2 link between switches which are running a
specialized trunking protocol. Trunks carry the traffic of multiple VLANs over
physical links (multiplexing) and enable the extension of a single Layer 2 VLAN
between switches.
If frames from a single VLAN traverse a trunk link, a
trunking protocol must mark the frame to identify its associated VLAN as the
frame is placed onto the trunk link. The receiving switch then knows the frames
VLAN of origin and can process the frame accordingly.
On the receiving
switch, the VLAN identifier is removed when the frame is forwarded onto an
access link associated with its VLAN.