LAN Switching Basics

  • – Enables dedicated access
  •  – Eliminates collisions and increases capacity
  •  – Supports multiple conversations at the same time

First of all, it’s important to understand the reason that we use LAN switching. Basically, they do this to provide what we called earlier as micro-segmentation. Again, micro-segmentation provides dedicated bandwidth for each user on the network.What this is going to do is eliminate collisions in our network, and it’s going to effectively increase the capacity for each station connected to the network.It’ll also support multiple, simultaneous conversations at any given time, and this will dramatically improve the bandwidth that’s available, and it’ll dramatically improve the scalability in our network.

LAN Switch Operation

So let’s take a look at the fundamental operation of a LAN switch to see what it can do for us. As you can see indicated in the diagram, we have some data that we need to transmit from Station A to Station B.

Now, as we watch this traffic go through the network, remember that the switch operates at Layer 2. What that means is the switch has the ability to look at the MAC-layer address, the Media Access Control address, that’s on each frame as it goes through the network.

And we’re going to see that the switch actually looks at the traffic as it goes through to pick off that MAC address and store it in an address table.So, as the traffic goes through, you can see that we’ve made an entry into this table in terms of which station and the port that it’s connected to on the switch.

Now what happens, once that frame of data is in the switch, we have no choice but to flood it to all ports. The reason that we flood it to all ports is because we don’t know where the destination station resides.

Once that address entry is made into the table, though, when we have a response coming back from Station B, going back to Station A, we now know where Station A is connected to the network.

So what we do is we transmit our data into the switch,but notice the switch doesn’t flood that traffic this time, it sends it only out port number 3. The reason is because we know exactly where Station A is on the network, because of that original transmission we made.On that original transmission we were able to note where that MAC address came from.

That allows us to more efficiently deliver that traffic in the network.

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