9 VLAN CONFIGURATIONWhen configuring VLAN, go to these sections for information you are interestedin:■ “Introduction to VLAN” on page 83■ “Configuring Basic VLAN Attributes” on page 86■ “Basic VLAN Interface Configuration” on page 86■ “Port-Based VLAN Configuration” on page 87■ “MAC Address-Based VLAN Configuration” on page 91■ “Protocol-Based VLAN Configuration” on page 92■ “Configuring IP-Subnet-Based VLAN” on page 94■ “Displaying and Maintaining VLAN” on page 95■ “VLAN Configuration Example” on page 95Introduction to VLANVLAN Overview Ethernet is a network technology based on the Carrier Sense MultipleAccess/Collision Detect (CSMA/CD) mechanism. As the medium is shared in anEthernet, network performance may degrade as the number of hosts on thenetwork is increasing. If the number of the hosts in the network reaches a certainlevel, problems caused by collisions, broadcasts, and so on emerge, which maycause the network operating improperly. In addition to the function thatsuppresses collisions (which can also be achieved by interconnecting LANs), virtualLAN (VLAN) can also isolate broadcast packets. VLAN divides a LAN into multiplelogical LANs with each being a broadcast domain. Hosts in the same VLAN cancommunicate with each other like in a LAN. However, hosts from different VLANscannot communicate directly. In this way, broadcast packets are confined to asingle VLAN, as illustrated in the following figure.
