Section 1. VLANs and Trunk Links
ICND1 introduced the basics of VLANs and inter-VLAN routing through a router on a stick. As previously written, switches operate on Layer 2 of the OSI model and routers operate on Layer 3. Switches increase the number of collision domains, which in turn decreases the amount of collisions in a network; routers increase the number of broadcast domains, while reducing their size.
Prior to the introduction of VLANs, network designers segmented large Layer 2 networks with routers. A router would be installed between the two networks. All data communication between the two would pass through the router, and the broadcast domain was limited to the physical location of the network.
VLANs introduced a way to logically ...