All language subtitles for 2_Basics of Networking

When most people think
of the Internet,

they think of a
magical cloud that

lets you access your
favorite websites,

shop online, and

you assumingly endless
stream of cat pictures,

but there isn't any
magic involved.

There's no mysterious entity

that grants us a cat
picture on-demand.

The Internet is just
an interconnection

of computers around the world,

like a giant spider web that
brings all of us together.

We call the interconnection
of computers a network.

Computers in a network can

talk to each other and
send data to one another.

You can create a simple network
with just two computers.

In fact, you might already
have your own network

at home connecting all
of your home devices.

Let's think on a bigger scale.

What about the computers at
your school or workplace?

Are they in a network?
They sure are.

All of the computers there

are linked together
in a network.

Can we link your home, school,

and workplace's
networks together?

We absolutely can.

Your workplace connects
to a bigger network,

and that network connects to

an even bigger network
and on and on.

Eventually, you've got

billions of computers
that are interconnected,

making up what we
call the Internet.

You, like most people,

probably access the
Internet through

a browser like Mozilla Firefox,

Google Chrome, Microsoft
Edge, or something else.

This is done through
the World Wide Web.

But don't make the
mistake of thinking

the Internet is the
World Wide Web.

The Internet is the
physical connection

of computers and wires
around the world.

The web is the information
on the Internet.

We use it to access
the Internet through

a link like www.google.com.

The World Wide Web isn't

the only way we can
access the Internet.

Your email, chat, and

file-sharing programs are also

ways you can access
the Internet.

In the IT field, managing,

building, and designing networks
is known as networking.

Networking is a super important
and large field in IT.

There are specialized jobs,
college degree programs,

and tons of literature dedicated
entirely to networking.

If you work in the IT field,

it's super critical that you

understand the fundamentals
of networking.

The Internet is composed

of a massive network
of satellites,

cellular networks,

and physical cables buried
underneath the ground.

We don't actually connect
to the Internet directly.

Instead, computers called

servers connect directly
to the Internet.

Servers store the
websites that we use,

like Wikipedia, Google,
Reddit, and BBC.

These websites serve content.

The machines that we use,

like our mobile phones,

laptops, video game consoles,

and more are called clients.

Clients request the
content like pictures,

websites from the servers.

Clients don't connect
directly to the Internet.

Instead, they
connect to a network

run by an Internet
service provider or ISP,

like CenturyLink, Level 3,

Comcast, Telefonica
and things like that.

ISPs have already
built networks and run

all the unnecessary physical
cabling that connects

millions of computers
together in one network.

They also connect to other
networks and other ISPs.

These other networks connect
to the networks of Google,

Reddit, universities,

basically all the other
networks in the world.

Together, they form
one giant network

of computers called
the Internet.

But how do the clients know
how to get to servers?

Well, how would you send
a letter to someone?

You'd put your address on
the letter and send it

to the address of the person

you're sending the letter to.

Computers have addresses
just like houses.

Computers on a network have

an identifier called
an IP address.

An IP address is
composed of digits

and numbers like 100.1.4.3.

When we want to
access a website,

we're actually going
to their IP address,

like 172.217.6.46.

Devices that can connect
to a network have

another unique identifier
called a MAC address.

MAC addresses are generally

permanent and hard-coded
onto a device.

A sample MAC address can
be something like this [82:4f:23:59:47:4].

When you send or receive
data through a network,

you need to have both an
IP and a MAC address.

You might be wondering
why we need to have

two different numbers
to identify something.

That's a good
question. Think again

of the letter analogy
we use before.

An IP address is
your house address,

while the MAC address is

the name of this
recipient of the letter.

You want to make sure
your letter gets to

the right location and
to the right person.

A more simplified example of

the letter delivery
would go like this.

I'm in New York city and I got

a letter that I want to
send to a friend, May.

May's halfway across
the world in Tokyo.

Our letter, we'll
go through lots of

places before it reaches her.

I put her name and
address on there

and I also put my name
and address on there too.

When I drop my letter
off at the post office,

the mail person looks at it.

He thinks, I don't know how
to get to Tokyo from here,

but there's a truck
that's headed to Texas.

He puts my letter in that truck

at the post office in Texas.

A mail person looks at
the letter and says,

I don't know how to get
to Tokyo from here,

but we have a truck
going to San Francisco.

She puts my letter
in that truck.

At the post office
in San Francisco,

yet another mail person
looks at my letter.

He says, there's
a plane headed to

Tokyo and puts the
letter on that plane.

When it finally reaches Tokyo,

the postman there says,

I know where May lives and
delivers the letter to her.

Obviously, there are
many more nuance

to mail delivery than
what I described,

but this process
is similar to how

information gets routed
across the Internet.

One thing to call out
is that data that's

sent through a network
is sent through packets.

There's little bits of data

and you guessed it,
ones and zeros.

It doesn't matter
if it's pictures,

email, music, or text.

When we move data
through the network,

we break them down into packets.

When a packet gets
to its destination,

it will rearrange
itself back in order.

Think of a packet like a letter.

Let's actually look at
this process again,

but this time we'll use IP
addresses and MAC addresses.

Natalie has a computer
with IP address

113.8.81.2 and she wants

to go to google.com and
search for pictures of cats.

Before she does that,
her computer has to send

a packet to ask google.com

if it can access their website.

Our packet knows google.com's

IP address is 172.217.6.46,

but it doesn't know how
to get there just yet.

The packet travels
from one place to

another at each
destination where it asks,

hey, do you know
where google.com is?

Eventually it'll be routed

to another destination that can

get the packet closer and
closer to google.com.

Once it reaches a
destination that can deliver

the packet to
aserver@google.com,

Google will send
Natalie a packet saying

she can access an unlimited
number of cat pictures.