- [Instructor] A router is used
to connect computers to other networks.
Routers come in several forms, your SOHO router,
those four-port or eight-port devices
that are used in homes and small offices
that are mainly used to connect to the internet.
Also, in bigger companies,
those black box devices, such as Cisco routers.
And they allow for more ports, 24, 48, 96.
And even servers.
If a server is equipped with multiple network adapters
and the proper software,
then that can act as a router as well.
Now, the router can be used as a connection to the internet,
as we said with the SOHO router, or on the LAN or WAN.
It could connect to other routers
and other portions of the network
or other networks within your company.
The device routes or sends packets
from one location to another.
So you have your packets of data
that are sent from the computer out through the network
through the router.
It routes the packets to a particular destination
anywhere in the world, really.
And it does this based on the IP addresses of other routers.
And that's what's important here.
You have to understand
that the routers all get an IP address.
And usually, this will be a static IP address.
Let's illustrate this.
Here, we have an illustration of a network.
And here, we have a switch
with three computers connected to it.
We have a desktop computer, a laptop and a server.
Doesn't really matter.
They're all part of the LAN, the local area network,
connected to the switch.
And then the switch has a connection to the router.
The router then connects out to the internet,
which is often depicted as a cloud.
And then, we have servers out on the internet.
And it doesn't really matter exactly
what they are or where they are,
except for we wanna know the IP address.
That's what's important.
So if you look here at our router,
this is allowing all these computers
access through the internet to the servers.
Here, we have a local area network IP address, 10.0.0.1.
That's the router's local address or ethernet address.
And that is also considered the gateway address.
If you configure TCP/IP on these computers,
you'll set up the gateway address as 10.0.0.1.
But the router has another IP address.
This is a multi-homed device.
It has two network adapters,
one for the ethernet to the LAN,
and one which is serial, out to the internet.
And that serial connection is using a public IP address,
207.172.15.50.
That's a visible IP address on the internet.
People out on the internet can see that IP address.
And this router can see other computers
on the internet as well.
For example, these computers here, 208.96.234.193 and .194.
These are two servers at some company
that this router can make a connection to.
And it doesn't really matter what they are exactly,
but they need to be public IP addresses
that the router can see.
So this is an example of the IP address structure.
And what happens is the router takes all the information,
all the data, from these computers and kind of re-wraps it.
Instead of the information being sent on the 10 network
once it goes through the router,
it gets changed to a public IP address.
Let's take a look at one of our SOHO routers
that I have in the lab here.
Here's an AC1750 SOHO four-port router.
And it also acts as a wireless access point.
And it has the LAN and WAN connections
that we just described.
Here's the local area network connection.
And its IP address is 192.168.0.1.
And that's the default for a TP-Link device.
192.168.0.1, that's a private IP address.
And then all the computers
will be automatically given IP addresses on this network.
For example, 192.168.0.100 and .101, and so on.
That's the local area connection
that allows all the computers on my little lab here
to talk to each other.
But it also enables a connection out to the internet.
And it does that through the WAN connection,
the wide area network connection.
But the WAN address is 64.121.138.225.
So that is the wide area network connection
that allows us access to any server
or any other computer around the world.
And you can see the device has a different subnet mask
and gateway and DNS servers
that are out on the internet at my ISP,
at the internet service provider, 208.59.247.45 and .46.
Also notice that the WAN connection is a dynamic IP.
I get that IP address from the internet service provider.
And again, I'll probably change that
at the end of these videos.
But the local area connection is a static connection.
That is the default address.
You can change it if you want,
but normally, you would manually input that
and leave it as that IP address
and have it act as a static address.
Keep in mind this address acts as the gateway address
for your client computers.
So if you have a client who is 192.168.0.100,
it will use this IP address as the gateway address.
So that's just a quick example
of the LAN and WAN connections on a basic SOHO router.
Okay, here's another diagram of a network.
This time, we have two local area networks
and they're in different geographical areas.
Let's say we have a company with two offices
in two different states or two different countries.
Well, here, we have LAN 29.
And we could say this is in New York City.
And over here, we have LAN 30.
And we could say that's in Los Angeles, just as an example.
LAN 29 uses an internal IP network of 172.29.0.0.
The Los Angeles LAN, LAN 30, uses an IP network 172.30.0.0.
And you could use whatever you want internally
because they're private IPs.
You just wanna make sure that they're different.
That this one is different from this one
and any other networks that you might have.
But then, you wanna connect them.
We have these computers connected to a switch here.
We wanna connect them through the internet.
So we install a router at each location.
The router in the LAN 29 location has two addresses,
the ethernet address,
which is on the same IP network as the LAN, 172.29.250.200,
and a serial address, which is a public address,
which can be seen by the internet.
And that's 65.43.18.1, just as an example.
The other LAN, LAN 30, that has a router with two addresses.
Same type of thing, ethernet address on the same IP network,
172.30.250.200,
and a serial address, which is seen on the internet,
it's public, 65.43.18.2.
So these two addresses, very similar,
just the last digit is one different.
So they will be able to see each other on the internet
and forward packets from each network through the internet.
And we just see a T-1 connection here.
That's just the type of network connection,
which we'll talk more about later.
But that's basically how the router's gonna work.
The router's gonna take that information from one LAN,
send it across the internet to another router.
That's always what happens.
To another router first,
and then it gets to its final destination,
whatever computer that is.
So all this that's happening here, this ethernet address
to serial address translation is just that.
It's known as network address translation or NAT.
And so, you wanna know that for the exam.
It's translating, it's taking these packets of information,
which are based on this IP network number,
and converting them over,
translating them to this network number over here.
Then, when they go to this router,
it gets converted or translated again
from this network number to this one.
And then, finally, to the final destination.
Every router is known as a hop.
So when you send information,
if you send information from this computer to here,
it goes hop, hop, hop.
That's a three-hop transmission right there.
And quite often, there's way more hops.
If you wanna see how many hops it takes
to get to a particular server or domain name,
use the tracert command.
But anyways, there's a little bit about routers,
a little basic description of how they work.
Take a look at your router, if you have one.
If you have a basic SOHO router,
log into it within your browser
and take a look at the LAN and the WAN connections.
Make a comparison of those.
Draw it out on paper.
See how it all works.
Check out your own network.
And that's it for this sub-lesson.