CertiGuide to Network+  9  Chapter 0011:  Network Hardware       9  IV  Layer 2 – Data Link Layer

Bridge 1 Brouter

Another layer 2 device, the switch, is rapidly replacing the hub at the layer 1 level. Recently, this higher performance device has been dropping rapidly in price, making it a cost effective choice to improve network performance.

Many switches look just like hubs – they’re boxes with 4, 8, or more ports, often-attaching cables with RJ-45 connectors. The difference is in functionality. Instead of repeating all the traffic out to all cables connected to it like a hub, a switch makes a virtual circuit between the sending and receiving devices, which stays up long enough for the traffic to pass. Like a bridge, it keeps track of which hardware MAC addresses are associated with each port, and sends out traffic only to those ports for which it destined. In this way it is similar to a router on the 3rd layer, the difference being that a switch directs traffic among devices on a single LAN, and a router directs traffic among multiple LAN’s.

The advantages of a switch over a hub are:

1. Full wire speed
   
   
2. Full-duplex operation
   
   
3. A collision free domain
   
   
4. Improves performance

   Figure 38: Switch

   
   

Bridge 1 Brouter