3Com 2000 TR Virtual LANs Vlans, What is a Vlan, Advantages of Vlan, Port-Based Distribution

Virtual LANs (VLANS)

What is a VLAN

A VLAN is defined as a group of location- and topol- ogy- independent devices that communicate as though they were on the same physical LAN. This means that they are not restricted by the hardware that physically connects them, and segments are defined by flexible user groups created by the user. For example, with VLANS, the user can define a net- work according to:

Department Groups—A VLAN could be created for the Marketing Department, another VLAN for the Finance Department, and still another for the Devel- opment Department.

Hierarchical Groups—A VLAN could be created for directors, another for managers, and still another for general staff.

Usage Groups—A VLAN could be created for Email users, another for multimedia users, and so on.

Advantages of VLAN

All 802 media and shared media support VLANs. In addition, implementing VLANs:

■Eases the change of devices

■Helps control broadcast traffic

■Provides extra security

Virtual LANs (VLANS) 2-7

VLANs facilitate the administration of logical groups of stations that can communicate as though they were on the same LAN. VLANs also facilitate moves, adds, and changes of members of logical groups.

Traffic between VLANs is firewalled. This limits the propagation of multicast and broadcast traffic between VLANs.

Each distinct VLAN is uniquely identified throughout the bridged LAN. A consistent representation of a VLAN exists across a VLAN fabric (including FE and ATM). This means that the shared VLAN knowledge of a particular packet remains the same as the packet travels from one point to another.

Port-Based Distribution

The switch uses a port-based approach to VLAN functionality. This approach allows bridges to classify all received tagged and untagged frames as belong- ing to a particular VLAN.

NOTE: In port-based VLAN operation, the VLAN clas- sification of an untagged frame is implicitly deter- mined and bases on the port of arrival of the frame. This facility requires association of a VLAN ID with each of the bridge’s ports. Only received frames lack- ing an explicit VLAN ID are subject to this impilcit clas- sification.

Using the port-based approach, a specific VLAN ID is associated with each bridge port. This VLAN ID, known as a Port VLAN Idendtifier (PVID), provides the VLAN classification for frames received through that port. This value may be manager configured.