Virtual LANs
Virtual LANs (VLANs) are used to segment network traffic. VLANs offer many benefits to an organization because they allow the segmentation of network users and resources that are connected administratively to defined ports on a switch. VLANs reduce network congestion and increase bandwidth. VLANs result in smaller broadcast domains.
VLANs do not need to be isolated to a single switch. They may span many switches throughout an organization. Extending VLANs is done by means of a trunking protocol. A trunking protocol propagates the definition of a VLAN to the entire local area network, whereas an access port accepts traffic for only a single VLAN. Trunking protocols work by encapsulating the Ethernet frame. Two common trunking protocols are the 802.1q standard and Cisco’s proprietary trunking protocol.
Cisco’s Inter-Switch Link (ISL) wraps the Ethernet frame, but it is not a standard used by all vendors. The 802.1q standard places information inside the Ethernet...