0:00:10.190,0:00:13.940
Hi! My name is Paola,and I am a software engineer at Microsoft.

0:00:13.940,0:00:20.130
Let's talk about how the internet works. My job relies on networks being able

0:00:20.130,0:00:26.489
to talk with one another, but back in the 1970s there was no standard method for this.

0:00:26.489,0:00:32.668
It took the work of Vint Cerf and Bob Kahn to invent the internetworking protocol, to make communication possible.

0:00:32.668,0:00:38.559
This invention laid the groundwork for what we now call the internet.

0:00:38.559,0:00:44.469
The internet is a network of networks. It links billions of devices together all

0:00:44.469,0:00:51.230
around the globe. So maybe you're connected with a laptop or a phone through wifi, then

0:00:51.230,0:00:56.999
that wifi connection connects to an internet service provider (or ISP), and that ISP connects

0:00:56.999,0:01:01.600
you to billions and billions of devices around the world through hundreds of thousands of

0:01:01.600,0:01:03.270
networks that are all interconnected.

0:01:05.600,0:01:15.670
One thing that most people do not appreciate is that the internet is really[br]a design philosophy and an architecture expressed in a set of protocols.

0:01:15.640,0:01:20.300
A protocol is a well known set of rules and standards, that if all parties

0:01:20.300,0:01:26.300
agree to use it will allow them to communicate without trouble.

0:01:26.300,0:01:31.910
How the internet actually physically works is less important than the fact that this design philosophy

0:01:31.910,0:01:37.710
has allowed the internet to adapt and absorb new communication technologies.

0:01:37.710,0:01:42.610
This is because in order for a new technology to use the internet in some fashion, it just needs to know which protocols to work with.

0:01:42.610,0:01:49.140
All the different devices on the internet have unique addresses.

0:01:49.140,0:01:54.350
An address on the internet is just a number, similar to a phone number or a sort of street address,

0:01:54.350,0:02:00.170
that's unique to each computer or device at the edge of the network.

0:02:00.170,0:02:04.690
This is similar to how most homes and businesses have a mailing address. You don't need to know a person to

0:02:04.690,0:02:09.110
send them a letter in the mail, but you do need to know their address and how to write

0:02:09.110,0:02:14.190
the address properly so the letter can be carried by a mail system to its destination.

0:02:14.190,0:02:19.870
The addressing system for computers on the internet is similar and it forms part of one

0:02:19.870,0:02:25.340
of the most important protocols used in internet communication simply called the internet protocol or IP.

0:02:25.340,0:02:31.890
A computer's address then is called its IP address. Visiting a website is really

0:02:31.900,0:02:36.620
just your computer asking another computer for information. Your computer sends a message

0:02:36.620,0:02:41.280
to the other computer's IP address and it also sends along its origin address, so the

0:02:41.280,0:02:48.450
other computer knows where to send its response.

0:02:46.280,0:02:49.450
You may have seen an IP address.It's just a bunch of numbers!

0:02:49.450,0:02:50.910
These numbers are organized in a hierarchy.

0:02:54.910,0:03:02.270
Just like a home address has a country, a city, a street, and a house number,

0:03:02.270,0:03:09.520
an IP address has many parts. Just like all digital data, each of these numbers is represented in bits.

0:03:09.520,0:03:14.470
Traditional IP addresses are 32 bits long, with 8 bits for each part of the address.

0:03:15.520,0:03:18.470
The earlier numbers usually identify the country and regional network of the device.

0:03:18.970,0:03:22.470
Then come the subnetworks, and then finally the address of the specific device.

0:03:22.470,0:03:30.470
This version of IP addressing is called IPv4.

0:03:30.470,0:03:34.050
It was designed in 1973 and was widely adopted in the early 80s,

0:03:30.470,0:03:38.050
and provides for more than 4 billion unique addresses for devices connecting to the internet.

0:03:40.420,0:03:47.340
But the internet has turned out to be much more popular than even Vint[br]Cerf imagined and 4 billion unique addresses won't be enough.

0:03:47.340,0:03:53.260
We're now in the middle of a multi-year transition to a longer IP address format

0:03:53.260,0:04:03.660
called IPv6, which uses 128 bits per address and provides over 340 undecillion unique addresses.

0:04:03.660,0:04:08.780
That's more than enough for every grain of sand on Earth to have its own IP address.

0:04:08.780,0:04:15.739
Most users never see or care about internet addresses.

0:04:15.739,0:04:23.410
A system called the domain name system or DNS associates names like www.example.com with the corresponding addresses.

0:04:23.410,0:04:29.160
Your computer uses the DNS to look up domain names and get the associated IP

0:04:29.160,0:04:33.290
address which is used to connect your computer to the destination on the internet.

0:04:33.290,0:04:38.050
And it goes a little something like this: (voice1) "Hey, hi there, I want to go to www.code.org."

0:04:38.050,0:04:49.900
(voice 2) "Mm.. yeah I don't know the IP address for that domain let me ask around.[br]Hey, do you know how to get to code.org?"

0:04:49.900,0:04:59.100
(voice 3) "Yeah, I got it right here it's 174.129.14.120."

0:04:59.100,0:05:04.500
(voice 2) "Oh okay, great, thanks. I'm gonna write that down and save it for later in case I need it again.

0:05:04.500,0:05:14.040
Hey here's that address you wanted." (voice 1) "Awesome! Thank you."

0:05:14.040,0:05:20.120
So how do we design a system for billions of devices to find any one of billions of different websites?

0:05:20.120,0:05:27.889
There is no way one DNS server can handle all the requests from all devices.

0:05:27.889,0:05:33.000
The answer is that DNS servers are connected in a distributed hierarchy, and are divided into zones,

0:05:33.000,0:05:40.699
splitting up responsibility for the major domains such as .org, .com, .net, etc.

0:05:40.699,0:05:48.030
DNS was originally created to be an open and public communication protocol for government

0:05:48.030,0:05:55.370
and educational institutions. Because of its openness, DNS is susceptible to cyber attacks.

0:05:55.370,0:06:02.540
An example attack is DNS spoofing. That's when a hacker taps into a DNS server and changes

0:06:02.540,0:06:09.479
it to match a domain name with the wrong IP address. This lets the attacker send people to an imposter website.

0:06:09.479,0:06:15.740
If this happens to you, you are vulnerable for more problems

0:06:15.740,0:06:23.870
because you are using that fake website as if it's real. The internet is huge and getting bigger everyday.

0:06:23.870,0:06:30.790
But the domain name system and internet protocol are designed to scale,

0:06:30.790,0:06:35.210
no matter how much the internet grows.