All language subtitles for 04 - Cisco Foundations - Basic IP Addressing-eng

>> I was having a conversation with my
aunt a couple weeks ago, who telecommutes,

works from home, works for a very large aircraft
company, and she was having some computer issues

and I was, I can't just fix something,
I always have to explain how it works.

And I said, "Okay, so you've
got your computer here.

You want to go that website right?

So you're going to have to access it somehow."

And she turns and looks at me and she goes,
"Oh, you mean like get to its IP address?"

[Laughing] And I said, "What do
you know about IP addresses?"

You know? And we kind of laughed and blew it
off, but my aunt is the least technical person

that I would, the least technical person I would
ever expect to wing out a term like IP address

to me, but that's how common it's become.

IP addressing rules the world.

It rules out everything communicates
on the internet

and rules the realm of our Cisco networks.

So of course it's going to be
a massive topic of this series.

So let's get started in it.

This is going to be basic IP addressing
where we understand what the IP address is.

Kind of your digital home.

You get to know your neighborhood.

What IP addresses are around you.

Who can you talk to without intervention.

How to find your friends on the
network using a protocol called ARP.

And then I would say just a massive concept
that I want to plant in your mind of,

how do you move around the network?

How do you combine layer 2 and layer
3 addresses together to communicate?

I'd like to think of IP addressing
as your digital home.

Because it works that way in the real world.

You have a house.

You have an address for your house of 55
West East Street that you tell people, "Hey,

if you want to visit my house
come to 55 West East Street."

And they go, "Okay, great, I'll
see you there at 5 o'clock."

And that's how they reach you.

Well every single device that is connected

to a network also has an
address known as an IP address.

That's how it communicates and that's
how people know how to reach it.

So an IP address is four octets.

So we'll just generate one here.

10.5.9.52.

Each one of these octets, each one of these
is an octet, has a value from 0 to 255.

Now there are some specific rules.

Like I just can't come in there and say,
"I want all zeros as my IP address."

There are all 255's and there's
even rules beyond that.

But we'll unfold those as we go.

For now, let's just know that
those are all possibilities.

I could have an IP address
10.5.255.9 and that works a-okay.

I mean these are all just potentials
that I could assign to my computer.

The rule is that every computer in the
network is going to need its own IP address.

I mean you don't share an address with your
neighbor and you don't to these devices.

It has to be unique.

Now these IP addresses are combined
with a subnet mask, always, and usually,

I'd say almost always, a default gateway.

In a nutshell, the IP address
defines your house or your location.

So, this is how people reach me
on the network and also the source

that I come from when I try to talk to them.

It's, you know, how they know to get back to
me when I'm trying to communicate to them.

The subnet mask defines your neighborhood.

Okay, wait a sec, let's figure out what
that means before we go any further.

I've got the IP address right here.

172.30.100.30.

I combine that with the subnet mask
255.255.255.0 is what I'm assigned to.

Now, you as an administrator, set this up.

You as an administrator assign those.

Now at a base level, and trust me it will get
more advanced that this, but I'd say this is,

for the vast majority of the networks of
the world, this is all you need to know.

Wherever you see 255, line that up
to the IP address and say, "Okay.

Those pieces of the address
represent my neighborhood or,

in technical words, my network."

My common ground that I communicate on.

Wherever I see a zero over here, that
represents who I am in that neighborhood or,

technically speaking, the
host of that neighborhood.

Okay. So we've got these two key pieces.

And before I even add in the default
gateway, I want to make sure we unpack

that and understand what that means.

So if I am this computer, 172.30.100.30,
and I'm plugged into a switch

and I have another computer over there that
I want to talk to who's 172.30.100.150.

Let's give them that IP address.

Now assuming I just don't want to write it,
they both have that subnet mask on there.

I go under this computer, right
here, and I generate a ping.

Now, what is a ping?

That's the first time we've seen it.

It actually stands for Packet Internet Groper.

That was the original name of it.

It actually has been changed to be a little more
politically correct, but the goal of a Ping is

to test connect network connectivity
and if you're using a Windows PC,

what it's actually doing is
putting the entire alphabet.

I mean A through Z into a packet along
with numbers 1, 2, 3, 4, 5, 6, 7, 8, 9.

It throws it all into a packet and
sends it to wherever you specify.

And then when the other side
receives it, it sends it back.

It's a way of testing that we can
communicate across the network, at least,

by sending the alphabet to a device.

And I will say Ping is your number
one network utility all the time.

That will be your friend in the network world.

So, with this host, let's
give a practical example.

I'm going to open up my command prompts,

that's where you would use Ping from,
and type in Ping 172.30.100.150.

Now, I'm typing it right here, but I'm pretty
sure it won't work because I don't think

that address exists, I'm just
showing you what I would type.

What happens then?

This computer and its internal
brain goes, "Okay.

I'm trying to Ping 172.30.100.150.

Interesting.

Because I'm looking at subnet mask and I realize
172.30.100.150 is in the same network as me."

How do I know?

Well, because he's in the same neighborhood.

He has the same first three octets
which I line up to my subnet mask

and realize he's in my neighborhood.

Now that's a huge point because what
that tells him is I'm able to reach

that device using a broadcast message.

[Pause] This is number one
concept of the day right here.

A broadcast message, meaning I can say,
[yelling] "Hellooooo neighborhood!"

I mean imagine yourself walking
out of your house with a megaphone

and going, "Helloooo my neighborhood!

[echoing sound] I would like to
speak to [echo sound] Susan Newport!"

You know [laughing].

You're just yelling out with this megaphone.

Everybody comes out of their house
and goes, "What's that guy doing?"

And they're all like, "Well, he's looking
for someone saying the name Susan Newport.

Well that was disturbing.

I'm going to go back in my house
because I'm not Susan Newport."

But somewhere down the street you hear
this little, [female voice] "Oh hello.

That's me."

And Susan comes running down to some, you know,
made-for-TV music and you guys are united.

Right? Where did I go with that?

So that's what the broadcast is there to do.

Sometimes these analogies just come to me
and they just turn odd halfway through.

He's going to send a broadcast, actually a very
specially crafted one known as ARP broadcast.

Address Resolution Protocol.

He's sending a message just like that,
you know, I' m looking for Susan example.

He's sending a message to his network
neighborhood saying, "Hello neighborhood!

I'm looking for 72.30.100.150.

Could that person please stand forward?"

Now all of the devices receive that message.

They're all disturbed.

But mind you, they have processors
that can handle being disturbed.

Broadcasts happen all the time
in a local area network and most

of them, these devices will ignore.

This is a perfect example.

He's saying, "Hello.

I'm trying to find 150."

They receive it and they go, "Well, I'm not 150.

I'm going back in my house."

This person receives it and goes, "Oh, oh.

That's me, that's me, that's me!

Let me send you, what's he trying to find?

Let me send you my MAC address."

Huge. ARP I call the MAC address sonar.

Its goal is to, if I know what IP address I'm
trying to access, which in this case is 150,

its goal is to figure out what
MAC address that device has.

And in this case it's easy
because we're both on same network.

This guy can go, "Hello 172.30.100.150.

Who are you?"

He responds back with a unicast.

What is that?

A direct message meaning he's going,
"Okay, well I saw that broadcast come in

and I saw the source MAC
address that you're coming from.

So I'm going to send a message
straight back to you."

Meaning I don't want to bother Bob
and Joe over here who's already had

to be bothered by your initial broadcast.

I'm just going to send my MAC address
directly back to you and now magic happens.

Now this guys goes, "I have all the pieces of
the puzzle that I need to send my alphabet A,B,

,D," you know, this is a PING message, right?

This is the payload of what I'm trying to
send to the destination IP address of 150

from a source IP address of 30, to a destination
MAC address, again we have these two levels

of addressing, we talked about
this in the previous nugget,

to the destination MAC address of,
well whatever this guy tells me.

These MAC addresses are also
a well known format.

Let me show you.

Open, oop, if I can get it open.

Open a command prompt here and
I'll do a, well let's do ARP-A,

which actually shows al l the MAC addresses.

It says, I want to know all the MAC
addresses that you know about on your network.

And, you know, I've got my own
little network here and this is me.

I'm 172.30.100.150.

He's like oh well of course
I know my own MAC address.

I learned about that because that's me, but I've
also learned about the MAC address of my router.

These are all, let me give
you the format of the MAC.

MAC addresses are all 12
characters long, hexadecimal.

That means you have the option of
0 through 9 at your disposable,

as well as A through F. The
way that they look can differ.

Windows formats them with, you know, 00-11-11,
you know, it uses that kind of format.

I've seen plenty of other devices that
format them like, you know, zero, zero:55:11.

Other devices, yet, go in there, as a matter of
fact Cisco does this a lot, and says 0014-5192-,

I mean you might go, "Well, come on!

What's the standard?"

They're all valid standards.

It just depends how the person decided to
format on it, but here's the common ground.

They all have 12 characters.

They all have values that will be 0 through 9
or A through F for each one of those characters.

So, my computer sends the broadcast message
out, gets the MAC address of this device back.

Once that happens, he has everything
that he needs to send his little A, B, C,

D or whatever you're trying to send.

You're sending an MP3 file, an e-mail, or
whatever you're trying to send over to that guy.

He's got everything that he needs.

The destination MAC address.

The source MAC address, of
course, because he knows who he is.

Now that is sent in here and
our switch does the magic.

Remember, that's what switches do.

Talked about that in the last nugget.

These are layer 2 devices.

They learn MAC addresses.

So as soon as he sings this, or as soon as he
sees this PING message comes in and says, "Oh,

I see," as a matter of fact, he
doesn't even see the IP addresses.

His functionality is limited.

He doesn't even see what the message is.

All this switch does is say, "Okay I see the
destination MAC address you're trying to go to

and I looked and I learned that that guy
goes out port, you know, 9, on these.

So I'm going to send that right out here.

He receives the alphabet, he replies
back, kind of flips these around,

says here's the source, here's the destination.

So that is, oh, if I could emphasize
how amazingly important that concept is,

and I know some of you are
going, "Okay I get all that.

I get that, but what's the dog?"

[Laughing] I just realized
I have a dog on my site.

This is ARP.

That's what ARP is.

ARP is a broadcast protocol.

It's like that loud dog in your neighborhood.

That's the analogy I was planning to use
before, you know "Sound of Music" and Susan

and everything else came out in my brain.

There's a dog barking saying, "Hello, hello!

Who is, who is?"

You know and tried to resolve
the MAC address that way.

But that's how it works.

So, before I move on.

Two more key facts.

One, so that's what the [pause] subnet mask is.

That's also, well hang on I said that backwards.

That's what the IP address.

That's also what this subnet mask is.

But we did everything that we did right
there without the use of default gateway.

And that's why I said usually a default gateway.

In rare, rare, rare, rare,
circumstances you might have that kind

of network and that's all you want.

You've got a bunch of devices plugged into a
switch and you just want them to communicate,

you don't need a default gateway.

Because I know you already have
a feeling of where this is going.

So what's the default gateway used for?

[Pause] Get's you off your network.

Gets you to some other network, which in
today's world most of the time is the internet.

It doesn't always have to be,
but most of the time it is.

So, this guy, let me fill this key piece
in, he is that 172.30.100.30 and I'll use

that same story from the last nugget.

He wants to go to the Bank of Arizona, right?

So I go to a web browser and
type in Bankofarizona.com.

The web browser, actually the
PC goes out and finds out, "Oh,

the Bank of Arizona is the
IP address 216.60.18.8."

Let's write that up here.

216.60.18.8.

Come on , somebody is feeling
this puzzle piece fit right now.

I can feel it.

You're listening to me and
you're like, "Ugh, ugh, wait,

are you going to say what I
think you're going to say?

I think so."

So, going in here, he looks
at his subnet mask, right?

He goes, "Okay, I'm in the 172 neighborhood."

He looks at this guy and goes, "Whoa!

Stop the train right there.

Not in my neighborhood."

Now you can go through the rest of this and say
I'm in 30, he's in 60, I'm on 100, he's in 18.

I mean these are as far apart as they could
possibly be in the neighborhood world,

but all it takes is just one of
these numbers to be different

and he realizes this is not my
neighborhood so, fit that piece together.

He realizes I can't send an Arp
message and reach that IP address.

Why not? Because that is
mission number two of a router.

Remember router's mission number
one is to get you where you need

to go based on IP address information.

But mission number two is I stop broadcasts.

That's really, when I, in the
very opening nugget, I said,

"What's the fundamental function of the router?"

It is to separate networks.

This is how it does it.

It keeps all of this broadcast traffic over here
and all of this broadcast traffic over here.

Now, keep in mind there's
thousands and millions of routers

out on the internet all keeping their
own broadcast traffic where it belongs,

but it separates the broadcast traffic.

So he knows if he sends an ARP message,
a broadcast, it will flood this network,

but it will never, ever, ever reach Bank
of Arizona which is out here somewhere

in the cloud that he wants to get to.

Because as soon as it reaches
here, it bounces off.

Doing [phonetic].

You know? It gets dropped.

So, what he has to do, he goes, "Okay,
I realize this is not on my network.

I need to send this to my default gateway."

Okay. If you're at a point
where you're like, "Okay.

Hang on I need a process pause now."

What I'm about to say is probably the most
important thing you will hear the rest

of this day.

[Laughing] You can probably tell I'm
given to drama, but I'm kind of serious.

So what this guy does, is he says, "I'm
going to ARP, but not for this IP address.

Because he knows that will be dropped.

Instead, I'm going to send an ARP
message for my default gateway.

I want the MAC address for my default gateway

and this is the kind of packet
I'm going to form.

I'm going to send a Ping because
that's just what I did or, you know,

a $50.00 transfer or whatever
you're going to do.

Ping is the alphabet.

Right? A, B, C, D. I'm going to send a Ping
to the destination IP address of the bank.

The source IP address it's
going to come from is me.

The destination MAC address it's going to
go to is, come on, come on, fill it in.

The gateway.

The router.

This guy right here.

The source MAC address it's going to
go to or I should say come from, is me.

This is what allows him to send a Ping
message to the router because the switch,

remember the switch doesn't
even see the IP address.

I kind of drew a line right here.

No, it's right here.

So the gateway is plugged into the switch.

He sends the message to the switch.

The switch doesn't even see
the IP address he's going to.

They don't have this capability.

They just look at MAC addresses.

So, he sends it to the switch.

The switch says, "Okay, I'm going to send it
to the destination MAC address right here."

Which is the gateway.

The gateway gets it and he's like, "Ooh!

Ooh! Message for me!"

But then when he looks further, because these
guys are layer 3 devices, network layer,

he goes, "Ooh, this isn't for me.

This is for Bank of Arizona and I just
happen to know how to get you there.

I'm going to send you out
to the ISP as the next hop."

That is, oh ok, rewind those
six minutes and watch it again.

Then rewind it again, show your friends, rewind
it, like if I could just solidify that concept

in your mind, you've got
networking fundamentals.

Like that is such a big concept.

Okay. I don't know, like this is
related but not really at this point.

I just kind of threw it in there.

This is like okay so you're studying
for the exam, you got to know this,

but we'll just throw it in there for now.

There are three core class, okay, so right.

Take this.

Put it into a bucket, right?

Set it aside and say, "That is my mastery of
information, this is something I just need

to know if I have a question that asks me that."

For now, three core classes of IP addresses,
A, B, and C that we use in our networks today.

There are more, but those are
the three core that are in use.

I know, the address is a certain, you know what?

I'm not even going to go there.

When I put together that slide, you
could tell I was like, "Oh good.

Oh good. Oh good."

And then it popped in my head I'm like, "Oh
yeah, you'll need to know this for the exam."

And we will, I know a lot
of you are exam focused.

And we will get back to the classes of
address, believe me, that is important.

It's just right now this is so good.

I don't want to, I don't want to have you put
that concept we just talked about in a bucket,

and then, you know, almost get derailed and be
like, "Oh yeah, I have to study for the exam.

It's like I want to just take it and run
with it, which is what I'm doing right here.

I want to take that concept.

Let's open the bucket back up, right?

And I want to put it together
in network scenario as a whole.

This, this, right here is how you explain
to your friends and your spouse and your dog

and everybody else who will listen
to you, how you get to Google.

You are sitting right here on the network.

You have the IP address 172.30.100.50.

Notice the subnet masks.

So I immediately identify, that is my network,
because I line up those first three octets

and I have the default gateway
right here going to my router.

Now I tried to color code
these just because, you know,

when you're putting these things
together, you can't really fit it all.

So the blue represents one network.

So if, let's put the scenario in here.

I Ping, [pause] let's give
the example 172.30.50.250.

Which is this guy over here.

Right? So I type that message into my computer.

What happens?

This computer looks at it and goes, "Okay.

172. I like that, that's my network.

30. Ooh, I like that too that's my network.

Ooh, failure.

50. No, no, no no, I'm on the 100 network."

I immediately recognize it is a PC.

That is not on my network.

That, in my mind, says I cannot send an
ARP message for this address and expect it

to get there because I know there's a brick wall
of a router that's gonna receive that broadcast

and drop it because, you know,
it's going to say, "Well,

you know, broadcasts are not allowed.

I'm a router.

I stop broadcasts."

So this computer is smart enough to say,
"Well, I need to get to this address,

but I have to use my gateway to get there.

So, he will send an ARP message, but
it will be for this gateway right here.

It will say, "I am looking for 172.30.100.1.

I know some of you are looking at this.

Follow the lines.

That's for the next network.

So, "I am looking for 172.30.100.1.,"
says the ARP message.

Right here.

He goes, "Oh, okay great!

Here's my MAC address."

My MAC address.

My MAC address, let me fill in
the example, is 1111:1111:1111.

Again, one of the formats of the MAC address.

This guys goes, "Great.

That's fantastic.

I happen to be 111, oops, :1111:1111:1122.

That's my MAC address.

Just because Jeremy can write that really fast.

So, I'm going to create a packet.

I'm going to have that Ping
be the data that I'm sending.

It's the alphabet.

Destination IP address, now you fill in
this box, what is the destination IP?

[Pause] 172.30.50.250.

That's where I'm going.

That's my end destination.

That will not change.

I have the source IP address of who?

Me. 50. That's where I came from.

172.30.100.50.

And know that I'm just writing this in here
because I can't squeeze that whole address

in there, but it is the full
IP address in there.

So then I'm also going to add in
destination MAC address of 1111:1111:1111.

Who is that?

Gateway. Default gateway.

Router. That is able to get
me out of my neighborhood.

Source MAC address.

1111:1111:1122.

Right? SO that is now a crafted
packet that will work.

Comes into the switch.

Switch. What does it read?

MAC address info, that's it.

It goes, "okay, I know because I'm
looking at my MAC address table

that the destination MAC
address of this is out port 9."

Again, I'll go there.

So, that now delivers the
Ping message to this router.

Router gets it he's like, "Ooh, ooh, mail for
me, because I see my destination MAC address."

He then looks further and
says, "Oooh, that's not for me.

That's going to 172.30.50.250."

Looks at his routing table.

Comes over here.

Routing table has all the places he knows how to
reach and one of them happens to be 172.30.50.0.

Oh man I just, it's like
my hand moved without me

and it introduced a whole
lot of concepts right there.

/24 is a shorthand notation
for that subnet mask.

And that's all I'm going
to say about it right now.

We'll get there, it really has
to do with binary behind it.

The 0 address represents the network.

Meaning I am not allowed to use 172.30.50.0
and assign that to any computer on that network

because this represents the network as a whole.

The only place I'm going to see that address,
that .0 address, is in a routing table

because that router says this is how
I know how to reach that network.

That identifies the whole network to me.

The 0 address.

While we're on the topic, the last address can
be used to send a broadcast message to everybody

on that network, but that's later.

That's like the classes of addresses, right?

Key information you'll need
to know, but not yet.

So this router looks at its routing table
and says, "Oh, I know how to get there.

Ooh, ooh. And my routing table tells me that
to get there, I need to send it to 10.5.1.2."

[Pause] How did it know that?

Well that's where you got
involved as a Cisco admin.

We have to get paid for something, right?

You went onto that router and educated it.

You could either educate it
statically and say, "Hey router,

to get to that network go to that IP address."

That's considered your next hop IP address or
you can let the routers do the work for you

and use something known as
a dynamic routing protocol.

But, again, more on that later.

For now, we'll just say the router knows.

The router knows how to get
there, so what does it do?

Because we're talking foundations here.

It will tear off, I'm busting out a red marker,

tear off the original source
and destination MAC address.

Because it doesn't need it anymore.

That was valid for this network to allow
these guys to talk, but now it will replace it

with the source and destination, and
for now, we'll just say MAC address.

It could be other things depending on the kind
of network, but most of the time it will be.

It will replace it with this MAC
address and that MAC address.

A new source and a new destination.

Which will be different from this one.

Every network card in the world
has its own unique MAC address.

So, you'll never have a duplicate of
those unless you buy really cheap,

knockoff network cards, at
which point, buyer beware.

So, he replaces and says, "Okay,
I'm going to do the ARP here.

I've got a new source.

A new destination."

Put that on there and that
gets the packet to right here.

This guy looks at his routing table and he goes,
again, this never changed, this never changed.

He goes, "Ooh, ooh.

I've got a message here from 172.30.50.250,"
and I'm looking at my router and going matter

of fact I am plugged right into that network.

He'll actually see a route in his routing table.

172.30.50.0 send it out your
Ethernet interface right here.

You know? It'll be right in there,
he's like, "Oh, I'm plugged into it.

Great." So what I will do is I
will send ARP message to find

out what the MAC address
of this server really is.

Because I know that's where I have to go.

So it resolves, via an ARP message, his
MAC address puts itself as the new source

and now we have the Ping
message that goes right here.

Isn't that amazing?

It's the same thing very similar to what
I was talking about in the last nugget,

I just like covering this multiple times because
it's a huge concept and I want it to go deep.

It's got to go deep in you because
this is the core of how networks work.

This is also the core of
everything troubleshooting

if your network is not working is this,
this little layer 2/layer3 address game

to help us move all around the network.

An analogy, if you're an analogy
kind of a visual person like I am.

I think of this layer 3/layer
2 as like a GPS system.

Where I'm sitting here in Arizona and
I want to drive my car up to Canada.

You know. We'll say 1,500 miles away.

Now, I know that I need to get there
and that's what I put in my GPS system,

but I have to have all these waypoints,
because I'm a man, I'm not a machine.

I have to get gas, I have to get coffee,
I have to get food along the way.

But in all of these little waypoints, I
never, you know, replace the end destination

in my GPS system with a waypoint.

You know, if I'm like, "Okay I want to
stop at the Circle K here on the corner,

that's waypoint number three," but I'm
never going to lose, I'm going to Canada.

You know I'm going to 55 North Elm Street in
Canada because if I do then I'll just stop

in at Circle K and get stuck there forever and
that's where I'll live my life and then die.

Which is what would happen to a packet.

So all of these are the layer 2 addresses.

We have to have these to get hop
by hop by hop by hop, you know,

to reach the different devices and, for
every single network needs its own set

of layer 2 addresses, but all along we keep
this the same because otherwise we lose

where we originally came from
and where we're finally going.

Poof! All my scribbles disappear.

And there's one more thing I wanted to add.

I added this internet cloud here for a reason.

When my device sends data and it ends up
reaching this router, that's again the goal

of the router is to figure out where to
send that data based on its IP address.

If I'm sending it to the server, it's going
to go, "Okay, I know how to get there.

I go out this cable right here."

If I'm sending to something
that's not this IP address,

it's likely going to have
something called a default route.

A default route looks like all zeros.

It's kind of like a default
gateway for a router.

But routers don't have default
gateways because they're routers,

and they are the default
gateway that things go to.

So, it has what's called a default
route that says, "You know what?

If you don't know where to
send it little router,

why don't you send this off to the internet?"

Now, I know in the picture, and you'll see
it in diagrams all the time, it looks like,

okay, it's the "Finding Nemo" right?

Its like, "Go fish.

Find your home on the internet."

But really it's far more technical than that.

There's really a router right here at your ISP.

You know? Whoever your ISP is, it says,
"Here's the MAC address of that router,

I will send it there," and this little
layer 2/layer 3 game goes all the way

until it finds whatever server you're
trying to reach out here on the internet.

So the router is the decision point.

Most of them have a default
route for the internet.

Now, how come?

Is there a way that this guy could actually
know every single network in the internet?

Actually there is.

It's something called, BGP,
which is the protocol

that holds all of the routes of the internet.

But, 90 percent, if not more, of the routers
just don't have the capacity for that.

You're Linksys or Netgear at home.

No way. Most Cisco routers that you use
[pause] in small office, home office,

small mid-size networks, won't have the memory
capacity to hold the BGP and when you get

into the realm it just becomes massive.

So instead, what we do is say you know, "Okay,
I know specifically how to get to that one.

I know specifically how to get here
and there and to all my networks inside

of my organization, but when it comes to the
internet, I'm going to use that default route,"

which says, "Here's how you
reach everything else."

So what did we see here and what
do I want you to do with it?

Well what we saw is the IP
addressing, the fundamentals of it,

we saw how the devices are addressed, how they
figure out what neighborhood they are based

on their subnet mask and finding
their friends using the ARP,

and also finding their default gateway
if they want to be able to get off

of their network or get out their neighborhood.

But I would say the most important
concept of all was that culmination

of how the layer 2/layer 3 addressing
works together, works with each other

to help deliver the message
where it needs to go.

Now what I want you to do
with this is a few things.

And again, some major concepts
that we discussed here.

I want you to go on your computer,
whether it be at work or at home,

and start proving it to yourself.

First off, do an IP config and by the
way, if you are studying for the exam,

you will need to know basic command line
utilities like IP config, Ping, ARP,

you know the utilities that
I've been using so far,

and you can see that I have a local area
connection, this is my network card.

And right here I have an
IPv4 address 172.30.100.72.

I want you to, you know, find
out what your IP address is.

Find out what your subnet mask is.

What your default gateway is.

I want you to Ping your default gateway.

You know go in there and Ping it, [pause]
to make sure that you're getting responses.

You should get replies back
from your default gateway.

Then do an ARP-A to find out what the
MAC address of your default gateway is.

If you're curious, these
things last for five minutes.

If you don't use them for five minutes, they'll
disappear out of, it's called your ARP cash.

You can manually clear them doing an ARP-D.

And I can say, "Okay.

What's left?

Nothing. It's all gone."

So now when I Ping it again,
notice that I see it in there.

Now, here's an interesting test.

I'm like, "Do I want show this to you
or do I want to leave this to you?"

Try Pinging an internet address.

Do an ARP-E.

[Pause] I'll do it with you.

Just in case you don't have a computer nearby.

[Laughing] Wait a sec.

What are you watching me on?

So ARP-D. And I see there
is no ARP entries found.

Now I'm going to a Ping to an internet address.

4222. It's actually a DNS
server out in California.

I just Pinged that.

If I do an ARP-A, what do I expect to see there?

The MAC address of 4222 or something else?

[Pause] Hmm.

Something else.

Notice that I never figure out what
the MAC address of that device is.

How come? It's not on my network.

My computer is smart enough
to know, "Oh you have to,

you have to default gateway to get there."

So I know his MAC address,
that's how I get there,

but my computer will never, ever, ever know.

And nor will I have a way of ever finding
out unless I give them a phone call.

What the MAC address is of that destination
server I'm reaching because it's not

on my network, it's in another world.

So, do these kinds of things and I would say,
you know, if you're not too sure what to Ping,

you know, start trying to find other addresses.

Just like I know there is there's
25, that's my storage server

at my house, and I can start saying, "Okay.

Now that's starting to show up in the list."

You might go on the internet
and grab a fun utility called,

[pause] if I can type it in
here, "Angry IP Scanner."

Just a fun little guy.

Download the old version.

It's actually much simpler,
I think, than the new one.

Go with the old Windows version.

Stable and widely used.

Go for that.

And do a scan of all the IP addresses in
your house and create a network diagram.

You know? Draw it up.

Just like I've been doing all throughout.

You know, draw, okay you've got the computer.

Over here, here's his IP.

Here's his MAC address.

I've got, you know, the switch,
which probably is invisible.

I've got a router over here.

I've got some other devices.

My Nintendo Wii.

I've got, you know, my X-Box.

You know. Whatever else you
find on that or diagram it out.

Just to start really, you get the concept here.

I need you to take this and start using it.

Applying it to things that
you do every single day.

I hope this has been informative for you
and I'd like to thank you for viewing.