Part 05 – Layer 2 Data Link Part II Switches

In this section we revisit hubs and examine their limitations in the context of layers one through three. This discussion will set things up for the higher-level functions that occur at layer 3. Hubs are layer 1 devices that are pretty much obsolete these days with the widespread availability of inexpensive layer 2 switches. The primary limitation of hubs is that they send data out of all ports. This results in multiple collision domains on a single device, which is highly inefficient, not to mention very insecure. Layer 2 switches have the ability to direct traffic based upon layer 2 MAC addresses. This provides immediate relief in terms of data collisions by providing a single collision domain and isolation at the port level. However, broadcast isolation is not possible with layer 2 switches and network congestion is still present. Routers are the solution to this issue and we'll have a look at them in the next section covering Layer 3 of the OSI reference model.
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