Instructor: Now, before we start talking 2 2
about network hacking, 3 3
you need to have a basic understanding 4 4
on how networks work. 5 5
Now, we all know that a network usually contains 6 6
a number of clients connected to each other, 7 7
and clients usually connect to a network 8 8
in order to share data or share a resource. 9 9
A really good example of a resource 10 10
that we all have connected to networks 11 11
in order to access is the internet. 12 12
So, we connect to Wi-Fi networks and even wired networks 13 13
all the time just to access the internet. 14 14
Now, all networks, whether it's Wi-Fi or wired, 15 15
work on the same principle. 16 16
They have a device that is considered as server. 17 17
Now, in many cases, for example, in your home network, 18 18
this server is your router. 19 19
This is also referred to as an access point. 20 20
Now, this router or server or access point 21 21
is the only device that has access to the resource. 22 22
So, none of these clients have direct access 23 23
to the resource, even after connecting to the network. 24 24
The only way they can access the resource 25 25
is through the access point. 26 26
So, let's say, for example, you're client number one 27 27
and you connected to your home network 28 28
over Wi-Fi or over ethernet, over a cable 29 29
and then you opened your browser and you typed google.com. 30 30
What happens is your computer will send the request 31 31
to the access point asking for google.com. 32 32
The access point has access to the resource, 33 33
which is the internet in this example, 34 34
so it's gonna go and look for google.com. 35 35
It will receive google.com, 36 36
and it'll forward that response to your computer, 37 37
and as a result you will see the website 38 38
loading on your browser. 39 39
So if you actually go to your router at home 40 40
and look at it, you'll see at the back 41 41
it's connected through a cable to the wall 42 42
and this is how it's getting its internet access. 43 43
Therefore, it is the only device in your network 44 44
that has direct access to the resource 45 45
and none of your computers, 46 46
none of the computers connected to the network 47 47
can access the resource or can access the internet 48 48
without the router, without the access point. 49 49
So the only way for all of the connected clients 50 50
to access the resource is to go through the router. 51 51
Now, the data is transferred between clients 52 52
and the access point as packets. 53 53
So you can think of all of these arrows 54 54
as a series of packets being transmitted 55 55
between the client and the router as requests and responses. 56 56
Now, in Wi-Fi networks, 57 57
these packets are transmitted in the air. 58 58
Therefore, if you have a wireless card 59 59
and you're within range, you'll be able to capture 60 60
all of these requests and responses. 61 61
So, basically, you'll be able to see 62 62
anything that any computer 63 63
connected to the same network as you, 64 64
thus on the internet, 65 65
because they will have to send all of these data 66 66
to the access point, 67 67
and because they're sending this data in the air 68 68
because you're in a WiFi network, 69 69
you'll basically be able to capture 70 70
these requests and responses. 71 71
And you'll be able to see the URLs they visit, 72 72
the usernames, the passwords they enter, the chat messages. 73 73
Anything they do on the internet will be sent as packets 74 74
and therefore you'll be able to capture it and analyze it. 75 75
We'll talk more about that 76 76
and more about how networks work 77 77
as we go through the course 78 78
but this is enough to get you going 79 79
through the next few lectures, so that you can sniff data, 80 80
analyze it and start launching 81 81
some cool pre-connection attacks.