Understanding LAN Switching
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.