0:00:00.901,0:00:04.498
(upbeat piano and drum music)

0:00:10.024,0:00:11.551
- Hi. My name is Paola,

0:00:11.551,0:00:14.501
and I am a software engineer at Microsoft.

0:00:14.501,0:00:17.077
Let's talk about how the internet works.

0:00:17.077,0:00:19.933
My job relies on networks being able

0:00:19.933,0:00:21.930
to talk with one another.

0:00:21.930,0:00:24.774
But back in the 1970s, there was no

0:00:24.774,0:00:26.956
standard method for this.

0:00:26.956,0:00:29.821
It took the work of Vint Cerf and Bob Kahn

0:00:29.821,0:00:32.126
to invent the Internetworking Protocol

0:00:32.126,0:00:34.308
to make communication possible.

0:00:34.638,0:00:36.570
This invention laid the groundwork

0:00:36.570,0:00:38.975
for what we now call the internet.

0:00:39.566,0:00:42.045
- The internet is a network of networks.

0:00:42.045,0:00:45.503
It links billions of devices[br]together all around the globe.

0:00:46.723,0:00:48.706
Maybe you're connected with a laptop

0:00:48.706,0:00:50.903
or a phone through wifi.

0:00:50.903,0:00:52.525
But then that wifi connection

0:00:52.525,0:00:55.716
connects to an Internet[br]Service Provider, or ISP.

0:00:55.716,0:00:58.363
And that ISP connects you[br]to billions and billions

0:00:58.363,0:01:00.196
of devices around the world

0:01:00.196,0:01:02.123
through hundreds of thousands of networks

0:01:02.123,0:01:04.045
that are all interconnected.

0:01:05.465,0:01:08.682
One thing that most[br]people do not appreciate,

0:01:08.682,0:01:12.142
is that the internet is[br]really a design philosophy

0:01:12.142,0:01:16.108
and an architecture expressed[br]in a set of protocols.

0:01:16.598,0:01:19.629
A protocol is a well-known set[br]of rules and standards that,

0:01:19.629,0:01:21.417
if all parties agree to use it,

0:01:21.417,0:01:23.781
will allow them to[br]communicate without trouble.

0:01:24.927,0:01:28.799
How the internet actually[br]physically works is less important

0:01:28.799,0:01:31.761
than the fact that this[br]design philosophy has allowed

0:01:31.761,0:01:33.920
the internet to adapt and absorb

0:01:33.920,0:01:36.239
new communication technologies.

0:01:36.239,0:01:38.464
This is because in order[br]for a new technology

0:01:38.464,0:01:40.650
to use the internet in some fashion,

0:01:40.650,0:01:43.455
it just needs to know which[br]protocols to work with.

0:01:44.763,0:01:46.782
All the different devices on the internet

0:01:46.782,0:01:48.489
have unique addresses.

0:01:48.489,0:01:50.865
An address on the[br]internet is just a number,

0:01:50.865,0:01:54.082
similar to a phone number,[br]or a sort of street address

0:01:54.082,0:01:56.248
that's unique to each computer or device

0:01:56.248,0:01:57.682
at the edge of the network.

0:01:59.314,0:02:01.755
This is similar to how most[br]homes and businesses have

0:02:01.755,0:02:03.099
a mailing address.

0:02:03.099,0:02:04.499
You don't need to know a person

0:02:04.499,0:02:05.829
to send them a letter in the mail,

0:02:05.829,0:02:08.344
but you do need to know their address,

0:02:08.344,0:02:10.141
and how to write the address properly,

0:02:10.141,0:02:12.335
so the letter can be[br]carried by the mail system

0:02:12.335,0:02:13.886
to its destination.

0:02:14.246,0:02:15.854
The addressing system for computers

0:02:15.854,0:02:17.724
on the internet is similar,

0:02:18.114,0:02:20.645
and it forms part of one[br]of the most important

0:02:20.645,0:02:23.354
protocols used in internet communication,

0:02:23.354,0:02:26.235
simply called the[br]Internet Protocol, or IP.

0:02:26.958,0:02:30.072
A computer's address, then,[br]is called its IP address.

0:02:30.514,0:02:33.222
Visiting a website is really[br]just your computer asking

0:02:33.222,0:02:35.299
another computer for information.

0:02:35.299,0:02:37.627
Your computer sends a message[br]to the other computer's

0:02:37.627,0:02:41.011
IP address, and it also sends[br]along its origin address

0:02:41.011,0:02:43.673
so the other computer knows[br]where to send its response.

0:02:45.751,0:02:47.895
- You may have seen an IP address.

0:02:47.895,0:02:49.743
It's just a bunch of numbers.

0:02:50.043,0:02:52.795
These numbers are[br]organized in a hierarchy.

0:02:53.425,0:02:55.685
Just like a home address has a country,

0:02:55.685,0:02:58.635
a city, a street, and a house number,

0:02:58.635,0:03:01.242
an IP address has many parts.

0:03:01.472,0:03:03.250
Just like all digital data,

0:03:03.250,0:03:06.250
each of these numbers[br]is represented in bits.

0:03:06.655,0:03:09.985
Traditional IP addresses are 32 bits long,

0:03:09.985,0:03:13.540
with eight bits for each[br]part of the address.

0:03:13.540,0:03:15.947
The earlier numbers usually identify

0:03:15.947,0:03:18.653
the country and regional[br]network of the device.

0:03:18.653,0:03:20.570
Then come the subnetworks.

0:03:20.570,0:03:23.925
And then, finally, the address[br]of the specific device.

0:03:24.435,0:03:28.485
This version of IP[br]addressing is called IPv4.

0:03:28.485,0:03:30.968
It was designed in 1973,

0:03:30.968,0:03:33.386
and widely adopted in the early '80s,

0:03:33.386,0:03:36.729
and provides for more than[br]4 billion unique addresses

0:03:36.729,0:03:39.527
for devices connecting to the internet.

0:03:39.797,0:03:43.170
But the internet has turned[br]out to be much more popular

0:03:43.170,0:03:45.339
than even Vint Cerf imagined,

0:03:45.339,0:03:48.677
and 4 billion unique[br]addresses won't be enough.

0:03:48.677,0:03:51.461
We're now in the middle[br]of a multi-year transition

0:03:51.461,0:03:55.793
to a longer IP address format called IPv6,

0:03:55.793,0:03:59.545
which uses 128 bits per address,

0:03:59.545,0:04:04.545
and provides over 340[br]undecillion unique addresses.

0:04:05.130,0:04:08.009
That's more than enough for[br]every grain of sand on Earth

0:04:08.009,0:04:09.990
to have its own IP address.

0:04:10.805,0:04:14.869
- Most users never see or[br]care about internet addresses.

0:04:14.869,0:04:18.160
A system called the Domain[br]Name System, or DNS,

0:04:18.160,0:04:22.065
associates names, like www.example.com,

0:04:22.065,0:04:24.050
with the corresponding addresses.

0:04:24.050,0:04:27.185
Your computer uses the DNS[br]to look up domain names

0:04:27.185,0:04:30.206
and get the associated[br]IP address, which is used

0:04:30.206,0:04:33.099
to connect your computer to the[br]destination on the internet.

0:04:33.099,0:04:34.999
- [Voiceover] And it goes a[br]little something like this.

0:04:34.999,0:04:35.619
- Hey, hi there.

0:04:35.619,0:04:39.450
I want to go to www.code.org

0:04:41.313,0:04:45.011
- Yeah, well I don't know the[br]IP address for that domain.

0:04:45.011,0:04:46.729
Let me ask around.

0:04:46.859,0:04:49.836
Hey, anyone know how to get to a...

0:04:50.396,0:04:52.022
code.org?

0:04:53.292,0:04:54.347
- Yeah, I got it right here.

0:04:54.347,0:04:57.270
It's 174 dot 129

0:04:57.270,0:05:00.184
dot 14 dot 120.

0:05:00.514,0:05:01.842
- Oh, okay, great. Thanks.

0:05:01.842,0:05:04.096
Yeah, I'm gonna write that[br]down and save it for later

0:05:04.096,0:05:05.078
in case I need it.

0:05:05.078,0:05:06.758
Hey, here's that address you wanted.

0:05:07.048,0:05:08.574
- Awesome. Thank you.

0:05:10.527,0:05:13.792
(piano flourish)

0:05:13.792,0:05:17.359
- So how do we design a[br]system for billions of devices

0:05:17.359,0:05:21.108
to find any one of billions[br]of different websites?

0:05:21.388,0:05:24.097
There is no way one DNS server

0:05:24.097,0:05:27.413
can handle all of the[br]requests from all devices.

0:05:27.633,0:05:30.513
The answer is that DNS[br]servers are connected

0:05:30.513,0:05:33.816
in a distributed hierarchy,[br]and are divided into zones,

0:05:33.822,0:05:36.915
splitting up responsibility[br]for the major domains

0:05:36.915,0:05:40.899
such as .org, .com, .net, et cetera.

0:05:41.829,0:05:44.129
DNS was originally created to be

0:05:44.129,0:05:47.116
an open and public communication protocol

0:05:47.116,0:05:49.871
for government and[br]educational institutions.

0:05:49.871,0:05:51.589
Because of its openness,

0:05:51.589,0:05:54.706
DNS is susceptible to cyber attacks.

0:05:55.247,0:05:58.399
An example attack is DNS spoofing.

0:05:58.399,0:06:01.724
That's when a hacker[br]taps into a DNS server

0:06:01.724,0:06:04.450
and changes it to match a domain name

0:06:04.450,0:06:06.725
with the wrong IP address.

0:06:06.985,0:06:11.588
This lets the attacker send[br]people to one imposter website.

0:06:11.588,0:06:13.364
If this happens to you,

0:06:13.364,0:06:15.694
you are vulnerable for more problems

0:06:15.694,0:06:19.783
because you are using that[br]fake website as if it is real.

0:06:21.443,0:06:25.597
The internet is huge, and[br]getting bigger every day.

0:06:25.597,0:06:28.599
But the Domain Name System[br]and Internet Protocol

0:06:28.599,0:06:30.485
are designed to scale,

0:06:30.485,0:06:32.885
no matter how much the internet grows.