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- [Instructor] A router is used

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to connect computers to other networks.

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Routers come in several
forms, your SOHO router,

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those four-port or eight-port devices

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that are used in homes and small offices

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that are mainly used to
connect to the internet.

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Also, in bigger companies,

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those black box devices,
such as Cisco routers.

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And they allow for more ports, 24, 48, 96.

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And even servers.

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If a server is equipped with
multiple network adapters

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and the proper software,

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then that can act as a router as well.

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Now, the router can be used as
a connection to the internet,

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as we said with the SOHO
router, or on the LAN or WAN.

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It could connect to other routers

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and other portions of the network

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or other networks within your company.

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The device routes or sends packets

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from one location to another.

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So you have your packets of data

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that are sent from the computer
out through the network

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through the router.

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It routes the packets to
a particular destination

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anywhere in the world, really.

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And it does this based on the
IP addresses of other routers.

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And that's what's important here.

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You have to understand

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that the routers all get an IP address.

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And usually, this will
be a static IP address.

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Let's illustrate this.

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Here, we have an
illustration of a network.

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And here, we have a switch

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with three computers connected to it.

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We have a desktop computer,
a laptop and a server.

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Doesn't really matter.

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They're all part of the
LAN, the local area network,

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connected to the switch.

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And then the switch has a
connection to the router.

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The router then connects
out to the internet,

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which is often depicted as a cloud.

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And then, we have servers
out on the internet.

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And it doesn't really matter exactly

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what they are or where they are,

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except for we wanna know the IP address.

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That's what's important.

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So if you look here at our router,

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this is allowing all these computers

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access through the
internet to the servers.

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Here, we have a local area
network IP address, 10.0.0.1.

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That's the router's local
address or ethernet address.

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And that is also considered
the gateway address.

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If you configure TCP/IP
on these computers,

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you'll set up the gateway
address as 10.0.0.1.

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But the router has another IP address.

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This is a multi-homed device.

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It has two network adapters,

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one for the ethernet to the LAN,

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and one which is serial,
out to the internet.

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And that serial connection
is using a public IP address,

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207.172.15.50.

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That's a visible IP
address on the internet.

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People out on the internet
can see that IP address.

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And this router can see other computers

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on the internet as well.

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For example, these computers
here, 208.96.234.193 and .194.

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These are two servers at some company

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that this router can make a connection to.

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And it doesn't really matter
what they are exactly,

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but they need to be public IP addresses

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that the router can see.

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So this is an example of
the IP address structure.

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And what happens is the router
takes all the information,

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all the data, from these
computers and kind of re-wraps it.

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Instead of the information
being sent on the 10 network

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once it goes through the router,

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it gets changed to a public IP address.

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Let's take a look at
one of our SOHO routers

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that I have in the lab here.

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Here's an AC1750 SOHO four-port router.

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And it also acts as a
wireless access point.

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And it has the LAN and WAN connections

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that we just described.

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Here's the local area network connection.

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And its IP address is 192.168.0.1.

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And that's the default
for a TP-Link device.

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192.168.0.1, that's a private IP address.

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And then all the computers

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will be automatically given
IP addresses on this network.

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For example, 192.168.0.100
and .101, and so on.

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That's the local area connection

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that allows all the computers
on my little lab here

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to talk to each other.

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But it also enables a
connection out to the internet.

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And it does that through
the WAN connection,

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the wide area network connection.

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But the WAN address is 64.121.138.225.

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So that is the wide
area network connection

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that allows us access to any server

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or any other computer around the world.

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And you can see the device
has a different subnet mask

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and gateway and DNS servers

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that are out on the internet at my ISP,

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at the internet service
provider, 208.59.247.45 and .46.

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Also notice that the WAN
connection is a dynamic IP.

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I get that IP address from
the internet service provider.

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And again, I'll probably change that

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at the end of these videos.

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But the local area connection
is a static connection.

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That is the default address.

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You can change it if you want,

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but normally, you would
manually input that

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and leave it as that IP address

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and have it act as a static address.

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Keep in mind this address
acts as the gateway address

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for your client computers.

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So if you have a client
who is 192.168.0.100,

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it will use this IP address
as the gateway address.

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So that's just a quick example

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of the LAN and WAN connections
on a basic SOHO router.

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Okay, here's another diagram of a network.

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This time, we have two local area networks

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and they're in different
geographical areas.

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Let's say we have a
company with two offices

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in two different states or
two different countries.

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Well, here, we have LAN 29.

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And we could say this is in New York City.

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And over here, we have LAN 30.

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And we could say that's in Los
Angeles, just as an example.

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LAN 29 uses an internal
IP network of 172.29.0.0.

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The Los Angeles LAN, LAN 30,
uses an IP network 172.30.0.0.

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And you could use whatever
you want internally

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because they're private IPs.

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You just wanna make sure
that they're different.

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That this one is different from this one

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and any other networks
that you might have.

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But then, you wanna connect them.

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We have these computers
connected to a switch here.

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We have these computers
connected to a switch here.

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We wanna connect them
through the internet.

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So we install a router at each location.

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The router in the LAN 29
location has two addresses,

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the ethernet address,

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which is on the same IP network
as the LAN, 172.29.250.200,

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and a serial address,
which is a public address,

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which can be seen by the internet.

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And that's 65.43.18.1, just as an example.

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The other LAN, LAN 30, that has
a router with two addresses.

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Same type of thing, ethernet
address on the same IP network,

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172.30.250.200,

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and a serial address, which
is seen on the internet,

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it's public, 65.43.18.2.

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So these two addresses, very similar,

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just the last digit is one different.

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So they will be able to see
each other on the internet

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and forward packets from each
network through the internet.

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And we just see a T-1 connection here.

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That's just the type
of network connection,

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which we'll talk more about later.

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But that's basically how
the router's gonna work.

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The router's gonna take that
information from one LAN,

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send it across the
internet to another router.

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That's always what happens.

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To another router first,

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and then it gets to its final destination,

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whatever computer that is.

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So all this that's happening
here, this ethernet address

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to serial address
translation is just that.

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It's known as network
address translation or NAT.

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And so, you wanna know that for the exam.

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It's translating, it's taking
these packets of information,

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which are based on this IP network number,

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and converting them over,

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translating them to this
network number over here.

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Then, when they go to this router,

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it gets converted or translated again

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from this network number to this one.

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And then, finally, to
the final destination.

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Every router is known as a hop.

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So when you send information,

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if you send information
from this computer to here,

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it goes hop, hop, hop.

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That's a three-hop
transmission right there.

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And quite often, there's way more hops.

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If you wanna see how many hops it takes

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to get to a particular
server or domain name,

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use the tracert command.

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But anyways, there's a
little bit about routers,

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a little basic description
of how they work.

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Take a look at your
router, if you have one.

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If you have a basic SOHO router,

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log into it within your browser

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and take a look at the LAN
and the WAN connections.

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Make a comparison of those.

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Draw it out on paper.

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See how it all works.

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Check out your own network.

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And that's it for this sub-lesson.