Bridges And Switches - Layer 2 - Understanding LAN Switching

Bridges

Another way is to add bridges. In order to scale our networks we need to do something known as segmentation. And bridges provide a certain level of segmentation in our network.And bridges do this by adding a certain amount of intelligence into the network. Bridges operate at Layer 2, while hubs operate at Layer 1. So operating at Layer 2 gives us more intelligence in order to make an intelligent forwarding decision.

That's why we say that bridges are more intelligent than a hub, because they can actually listen in, or eavesdrop on the traffic going through the bridge, they can look at source and destination addresses, and they can build a table that allows them to make intelligent forwarding decisions.

They actually collect and pass frames between two network segments and while they're doing this they're making intelligent forwarding decisions. As a result, they can actually provide greater control of the traffic within our network.

Switches - Layer 2

To provide even better control we're going to look to switches to provide the most control in our network, at least at Layer 2. And as you can see in the diagram, have improved the model of traffic going through our network.

Getting back to our traffic analogy, as you can see looking at the highway here, we've actually subdivided the main highway so that each particular car has it's own lane that they can drive on through the network. And fundamentally, this is what we can provide in our data networks as well.So that when we look at our network we see that physically each station has its own cable into the network, well, conceptually we can think of this as each workstation having their own lane through the highway.Basically there is something known as micro-segmentation. That's a fancy way simply to say that each workstation gets its own dedicated segment through the network.

Switches versus Hubs

If we compare that with a hub or with a bridge, we're limited on the number of simultaneous conversations we can have at a time.Remember that if two stations tried to communicate in a hubbed environment, that caused something known as collisions. Well, in a switched environment we're not going to expect collisions because each workstation has its own dedicated path through the network.What that means in terms of bandwidth, and in terms of scalability, is we have dramatically more bandwidth in the network. Each station now will have a dedicated 10 megabits per second worth of bandwidth.

So when we look at our switches versus our hubs, and the top diagram, remember that we're looking at a hub. And this is when all of our traffic was fighting for the same fixed amount of bandwidth.Looking at the bottom diagram you can see that we've improved our traffic flow through the network, because we've provided a dedicated lane for each workstation.