A LAN is a Local Area Network.
We commonly define this as a group
of devices that are in the same broadcast domain.
In this example, we have two different switches.
One is the red switch and one is the blue switch.
On the red network, we have two devices that
are in one broadcast domain.
And on the blue switch, we have devices
that are on a completely different broadcast domain.
We might want this separation for security reasons.
Certainly this would have a separation
between these devices and these.
We might want to limit the number of broadcasts
that might be on a network.
So we might segment the network into smaller pieces.
And in many ways, this is a very straightforward way
to manage the network.
Because if somebody needs to be on the red network,
we connect them to the red switch.
And if someone needs to be on the blue network,
we connect them to the blue switch.
However, looking at this diagram,
we can immediately see a number of inefficiencies.
We've of course purchased two separate switches.
We are powering two separate switches,
and we're managing the configurations
on two separate switches.
All of these are duplicating the effort,
in some cases duplicating the cost we would need to maintain
both of these networks.
We can also see on these switches
that we're connecting two devices,
but we have a lot of empty interfaces on the switch.
So we've paid for a lot of switch
that ultimately we're not using.
It would be much more efficient and cost effective
if we could buy a single switch, maintain a single power
source for that switch and a single configuration,
and simply logically associate certain interfaces
on that switch to the red network
and logically associate other interfaces on that switch
to the blue network.
The switch itself would provide the separation
between the red network and the blue network,
and these devices still would not
be able to communicate directly to each other.
We refer to this virtualization of the local area network
as a VLAN.
This is grouping the devices still in their same broadcast
domain, but we're doing this across
the same physical device.
This means that we won't need separate switches.
We can instead have exactly the same functionality
on a single switch by implementing and configuring
VLANs for each of these individual interfaces.
Let's add even a third network.
So on this switch, we've configured
a red network, a blue network, and a green network.
And you can see that we've connected different devices
to these interfaces.
As the network administrator, we've
specifically configured the interfaces on the switch
to match a certain network.
So in this case, if you're connected to port one,
you're on the red network.
If you're connected to port nine,
you're on the blue network.
And if you're connected to port 17,
you're on the green network.
Of course, instead of using colors
we associate a VLAN with a number.
So the red network may be VLAN 1,
the blue network might be VLAN 2,
and the green network might be VLAN 3.
You can see that not only does this
make it easier to manage the network,
but now we can keep costs lower by having a single switch
instead of purchasing three separate switches
for these three VLANs.
A technology that has become rather commonplace
on our networks today is a VPN or a Virtual Private Network.
This is usually a combination of software and hardware
that allows us to securely send information
across a public network such as the internet.
Everything sent over that VPN connection is automatically
encrypted, which means if anyone in the middle
happens to capture this information,
they wouldn't be able to see or understand
anything in the conversation.
If you've used a VPN, then you certainly
are familiar with how that looks from the desktop
of your operating system.
But somewhere it's connecting to a separate device
and the device we're connecting to is a concentrator.
This can be a standalone device or it
may be integrated into a firewall
or some other multi-use device.
There are many different ways to deploy VPNs.
The example we have here is a hardware device
that may have specialized VPN or encryption hardware
inside of it.
But you can also configure VPN software that
might be running on a server.
Many VPN implementations have their own application
that can be installed in an operating system,
and you'll find that these days most modern operating
systems come included with some type of VPN client.
This means that you can still be secure when
using your laptop in a coffee shop
even if the wireless network in that coffee shop
is one that is open and not encrypted.
You would either use VPN software that's always
on and always connected or you would
have the option on your laptop to enable or turn
on the VPN capability.
When you do that, it creates an encrypted tunnel back
to the VPN concentrator, and now everything
sent from your laptop will be encrypted
across the wireless network of the coffee shop, the internet,
and any other links until it reaches that VPN concentrator.
At this point, the VPN concentrator
will receive that encrypted information.
It will decrypt the data and send that information
into the corporate network.
Any device that needs to send information back to the laptop
will send that information to the VPN concentrator.
The concentrator will encrypt that data,
send it over the encrypted tunnel,
and when it reaches your laptop, the laptop
will then decrypt that data so that it can be used locally.
This entire process happens behind the scenes
and is automatic when you enable your VPN software.