VLANs:
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| Virtual LANs |
A VLAN is a logical grouping of devices or users. These devices or users can be grouped by function, department application and so on, regardless of their physical segment location. VLAN configuration is done at the switch via switching fabric. A VLAN can be used to reduce collisions by separating broadcast domains within the switch. In other words, VLANs create separate broadcast domains in a switched network. Frame tagging at layer 2 does this. Frame tagging is a gaining recognition as the standard for implementing VLANs, and is recognized by IEEE 802.1q. Frame tagging uniquely assigns a VLAN ID to each frame. This identifier is understood and examined by each switch prior to any broadcasts or transmissions to other switches, routers, and end-stations devices. When the frame exits the network backbone, the switch removes the identifier before the frame is transmitted to the target end station. This effectively creates an environment with fewer collisions. The key to this is that ports in a VLAN share broadcasts, while ports not in that VLAN cannot share the broadcasts. Thus users in the same physical location can be members of different VLANs. We can plug existing hubs into a switch port and assign them a VLAN of their own to segregates users on the hubs. Frame filtering examines particular information about each frame. A filtering table is developed for each switch; this provides a high level of administrative control because it can examine many attributes of each frame. Frame filtering is slowly being erased and replaced by the frame tagging method.
