Content

| 2.1 |  | VLAN Basics |
| 2.1.5 |  | VLANs and bandwidth utilization |

When users attach to the same shared segment, all of them share the bandwidth of the segment. With every additional user on the shared medium there is less bandwidth available for each user. User network and application performance will begin to diminish if the bandwidth sharing becomes too great. The network administrator will need to take action because the users will be less productive. VLANs can offer more bandwidth to users than is inherent in a shared network.

Remember that each interface on a switch behaves like a port on a legacy bridge. Bridges filter traffic for the source segment. If a frame needs to cross the bridge, the bridge forwards the frame to the correct interface. If the bridge or switch does not know the destination port, it floods the frame to all ports in the broadcast domain (VLAN) except the source port. By assigning ports on a switch to different VLANs, it is possible to limit the number of switch ports out which flooded data gets sent.

In a switched environment, a station will usually see only traffic destined specifically for it. The switch will filter most of the other background traffic in the network. This allows the workstation to have full, dedicated bandwidth for sending or receiving interesting traffic. Unlike a shared-hub system where only one station can transmit at a time, a switched network allows many concurrent transmissions within a broadcast domain without directly affecting other stations inside or outside of the broadcast domain. In Figure , station pairs A/B, C/D, and E/F can all communicate without affecting the other station pairs.