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(upbeat piano and drum music)

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- Hi. My name is Paola,

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and I am a software engineer at Microsoft.

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Let's talk about how the internet works.

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My job relies on networks being able

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to talk with one another.

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But back in the 1970s, there was no

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standard method for this.

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It took the work of Vint Cerf and Bob Kahn

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to invent the Internetworking Protocol

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to make communication possible.

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This invention laid the groundwork

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for what we now call the internet.

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- The internet is a network of networks.

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It links billions of devices
together all around the globe.

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Maybe you're connected with a laptop

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or a phone through wifi.

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But then that wifi connection

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connects to an Internet
Service Provider, or ISP.

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And that ISP connects you
to billions and billions

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of devices around the world

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through hundreds of thousands of networks

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that are all interconnected.

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One thing that most
people do not appreciate,

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is that the internet is
really a design philosophy

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and an architecture expressed
in a set of protocols.

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A protocol is a well-known set
of rules and standards that,

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if all parties agree to use it,

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will allow them to
communicate without trouble.

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How the internet actually
physically works is less important

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than the fact that this
design philosophy has allowed

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the internet to adapt and absorb

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new communication technologies.

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This is because in order
for a new technology

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to use the internet in some fashion,

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it just needs to know which
protocols to work with.

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All the different devices on the internet

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have unique addresses.

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An address on the
internet is just a number,

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similar to a phone number,
or a sort of street address

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that's unique to each computer or device

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at the edge of the network.

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This is similar to how most
homes and businesses have

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a mailing address.

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You don't need to know a person

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to send them a letter in the mail,

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but you do need to know their address,

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and how to write the address properly,

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so the letter can be
carried by the mail system

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to its destination.

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The addressing system for computers

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on the internet is similar,

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and it forms part of one
of the most important

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protocols used in internet communication,

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simply called the
Internet Protocol, or IP.

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A computer's address, then,
is called its IP address.

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Visiting a website is really
just your computer asking

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another computer for information.

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Your computer sends a message
to the other computer's

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IP address, and it also sends
along its origin address

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so the other computer knows
where to send its response.

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- You may have seen an IP address.

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It's just a bunch of numbers.

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These numbers are
organized in a hierarchy.

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Just like a home address has a country,

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a city, a street, and a house number,

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an IP address has many parts.

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Just like all digital data,

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each of these numbers
is represented in bits.

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Traditional IP addresses are 32 bits long,

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with eight bits for each
part of the address.

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The earlier numbers usually identify

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the country and regional
network of the device.

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Then come the subnetworks.

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And then, finally, the address
of the specific device.

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This version of IP
addressing is called IPv4.

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It was designed in 1973,

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and widely adopted in the early '80s,

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and provides for more than
4 billion unique addresses

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for devices connecting to the internet.

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But the internet has turned
out to be much more popular

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than even Vint Cerf imagined,

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and 4 billion unique
addresses won't be enough.

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We're now in the middle
of a multi-year transition

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to a longer IP address format called IPv6,

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which uses 128 bits per address,

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and provides over 340
undecillion unique addresses.

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That's more than enough for
every grain of sand on Earth

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to have its own IP address.

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- Most users never see or
care about internet addresses.

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A system called the Domain
Name System, or DNS,

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associates names, like www.example.com,

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with the corresponding addresses.

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Your computer uses the DNS
to look up domain names

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and get the associated
IP address, which is used

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to connect your computer to the
destination on the internet.

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- [Voiceover] And it goes a
little something like this.

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- Hey, hi there.

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I want to go to www.code.org

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- Yeah, well I don't know the
IP address for that domain.

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Let me ask around.

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Hey, anyone know how to get to a...

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code.org?

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- Yeah, I got it right here.

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It's 174 dot 129

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dot 14 dot 120.

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- Oh, okay, great. Thanks.

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Yeah, I'm gonna write that
down and save it for later

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in case I need it.

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Hey, here's that address you wanted.

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- Awesome. Thank you.

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(piano flourish)

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- So how do we design a
system for billions of devices

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to find any one of billions
of different websites?

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There is no way one DNS server

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can handle all of the
requests from all devices.

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The answer is that DNS
servers are connected

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in a distributed hierarchy,
and are divided into zones,

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splitting up responsibility
for the major domains

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such as .org, .com, .net, et cetera.

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DNS was originally created to be

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an open and public communication protocol

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for government and
educational institutions.

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Because of its openness,

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DNS is susceptible to cyber attacks.

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An example attack is DNS spoofing.

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That's when a hacker
taps into a DNS server

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and changes it to match a domain name

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with the wrong IP address.

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This lets the attacker send
people to one imposter website.

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If this happens to you,

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you are vulnerable for more problems

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because you are using that
fake website as if it is real.

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The internet is huge, and
getting bigger every day.

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But the Domain Name System
and Internet Protocol

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are designed to scale,

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no matter how much the internet grows.