As you get into your networking career,
you're going to see a lot of different kinds of networking
devices.
And in your data center, some of them
will be very common to you.
In this video, we're going to go through some
of the most common network devices that you'll find.
One of the foundational components of networking
is the Ethernet hub.
This hub is what we call a multi-port repeater, which
means that any traffic going into one port on a hub
is automatically sent to all of the other interfaces
on that hub as well.
So you can plug into any place and see all of the traffic that
may be traversing the network.
We refer to this, in the OSI model,
as an OSI Layer 1 device, since it's really
taking the signal and forwarding all of the signal
to every other port regardless of what it happens to be.
When you're connected to a hub, you
are connected in half-duplex mode.
That means that you can send information
or you can receive information, but you can't do
both of those at the same time.
We're almost used to a full-duplex mode
in today's modern networks.
Because we're using switches.
But back when we were using hubs,
we didn't have the flexibility of having
a full-duplex connection.
That means that the more that we increase our speeds,
the less efficient the network is going to be.
Because as we're sending, we're going
to have to wait for everybody else
to finish what they're doing so that we can finally
send information.
You'll also find that hubs really only
come in two flavors-- a 10 megabit
and a 100 megabit version.
Although there was a specification in Ethernet
for higher speed hubs, the technology of switches
had already come out, so no manufacturer invested any time
in creating a gigabit hub.
So if you do run into a hub, it's
either going to run at 10 or 100 megabit.
And hubs are a little bit outdated.
They're difficult to find today.
There is some niche uses of these,
especially in doing network management and network
troubleshooting, but because they're only
running at 10 or 100 megabit, they
have very limited use today.
When switching hardware was introduced,
we quickly move from hubs to using switches.
And if you're connected to a network today,
you're undoubtedly connected to a switch.
These switches are able to move information
very quickly, because of the hardware inside of them.
This hardware is called an application-specific integrated
circuit, and we refer to this as an ASIC.
These ASICs are designed to move information across the network
based on what the destination hardware
address might be of a device.
We call these OSI Layer 2 devices,
because it's using that data link address to determine
where traffic goes.
This is a much more intelligent way
of sending traffic than a hub, which simply
sent all of the information to every single port
on the device.
Instead a switch is very specific.
If information is destined for a particular interface,
it sends that information to only that interface
on the switch.
Another advantage of switching technology
is that you can have a lot of interfaces on a single switch.
Some very large enterprise switches
can have hundreds of interfaces on one single chassis, which
makes it perfect for putting in the middle of a network
or in the middle of a data center.
Some switches can also provide power.
So you can plug in your voice over IP phone or an access
point, and all the power for that device
is coming directly from the switch.
Some switches are designed with Layer 3 functionality,
so they can effectively route information as well.
At that point, we're layering two devices together, a switch
and a router inside the same device.
And we tend to call those multi-layer switches, or Layer
3 switches, to designate that they can not only
switch information, but we can also use them as a router
as well.
Another common network device is a router.
A router is designed to send information
between different IP subnets.
We will often refer to this as a Layer 3 device, because it's
making its forwarding decision based on the Layer 3 address,
or the IP address, that might be within a network communication.
And that's why you'll hear people
refer to a Layer 2 device as a switch and a Layer 3 device
as a router.
And as I mentioned, there are some switches
that integrate routing functionality.
So one part of the switch can perform forwarding decisions
based on the Layer 2 address.
And other parts of that switch will route and perform
its forwarding decisions based on the Layer 3
address of that device.
These routers are often connecting IP addresses
on Ethernet.
But they can also be used to connect different network
types as well.
So you may be connecting a LAN with a WAN.
Or you may be connecting a copper network
to a fiber network.
And you want to be able to route between those routers
the perfect choice to use for that particular function.
Network security is also incredibly important.
And that's why another common device you'll find
on your network is a firewall.
Traditional firewalls can filter information
going through your network based on a port number.
This would be an OSI Layer 4 TCP port number or UDP port number.
Some modern firewalls can filter information
all the way up into Layer 7.
They recognize the exact application you're using
and can make decisions on whether to allow or block
that traffic based on the application that's
flowing through it.
Firewalls can also be used to encrypt information
in and out of your network.
If you need to connect to a remote side
but you want to send everything to that remote site in a very
secure way, you'll find that many firewalls provide
this IPsec encryption mechanism.
And we'll learn a lot more about that as we
progress through this Network Plus course.
Firewalls can also be used to do things like proxy traffic.
Not all firewalls provide this functionality.
But it is something that you might commonly
find in a firewall, so that you can
stop all of the communication and instead
have the firewall have that communication done
on your behalf.
And then once the firewall receives an answer
to that request, it then sends it to you internally.
And this allows the firewall to effectively get
in the middle of that conversation
and make sure there's nothing bad that might be traversing
that particular link.
When we refer to firewalls, we're talking about Layer 4
filtering.
But it's not unusual to see firewalls operating at Layer 3,
becoming routers as well.
There's many ways to connect firewalls.
This is one of the most common ways
you'll find to plug in a firewall on your network,
so that it's not only the firewall
protecting your network.
it's also the main router between the inside
and the outside of your network.
Another common network device you may find
is a wireless access point or while a WAP.
If you're working at home, you may
be accustomed to seeing a wireless router.
And it has the wireless antennas on the outside of it,
but it's also the router that's used inside of your network.
In those particular cases, the wireless access point
functionality is also built into the router.
But we would refer to those more appropriately
as wireless routers.
A WAP is something you might commonly see in a larger
enterprise environment.
It is simply a bridge.
It's extending an existing Ethernet network
that is on a wired network into something that is wireless.
And so it is an OSI Layer 2 device,
because it's making its forwarding decisions based
on the Mac address or the data link address
inside of those frames.
One of the mainstays of the common network device
is the modem.
Modem stands for modulator/demodulator.
And it's a way to take information that is digital,
convert it into an analog form, send that through a medium,
and on the other side, convert it back
into a digital form that can be then used by the computing
devices on the other side.
A very common modem uses standard phone lines.
We connect up to the phone line, we're
sending audio signals, which are those analog signals
across the phone lines.
And on both sides of the connections,
we have modems to convert those back into digital form.
It's very common to see these days
a modem being used on these plain old telephone
systems, or these POTS lines, for things like backup
and utility functions.
The bandwidths that are allowed by these modems
are very limited.
So they're really specifically used
for a different type of utility function or something
that doesn't require a lot of bandwidth.
A more modern modem might be one that we
find in our homes and our businesses that connect us up
to a DSL network.
These asynchronous DSL lines take the digital signals
and convert them into an analog and send them over the DSL link
to the other side.
You might also have, in your environment, a cable modem.
Cable modems don't work exactly like modulator/demodulator.
But they do provide that bridging functionality
that allows us to connect from our Ethernet network
onto the cable modem network.