Terminology referring to Virtual LANs often refers to a trunk or trunking. What is it?
When a single switch is not sufficient for a company, but the LAN extends over a set of them, the need arises to create Virtual LANs on each and enable communication between them. The first solution could be to use a port dedicated to the uplink for each VLAN. This would however lead to waste in terms of ports and cables; if the Virtual LANs common to two switches are n you must use n uplink cables. A better solution is to create a trunk or trunking: in other words, both switches are attributed a common port (trunk port) to all the VLANs that need to be transported. The switches tag each packet outbound of the trunk with a VLAN ID and each packet entering via trunking is forwarded on the right VLAN based on the VLAN ID. It is obvious that the two switches must use the same trunking protocol to communicate correctly via the trunk. There are different types of these protocols, which are often proprietary, and this could lead to inter-operational problems among different brands of switch
