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Now, before we start talking 2

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about network hacking, 3

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you need to have a basic understanding 4

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on how networks work. 5

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Now, we all know that a network usually contains 6

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a number of clients connected to each other, 7

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and clients usually connect to a network 8

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in order to share data or share a resource. 9

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A really good example of a resource 10

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that we all have connected to networks 11

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in order to access is the internet. 12

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So, we connect to Wi-Fi networks and even wired networks 13

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all the time just to access the internet. 14

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Now, all networks, whether it's Wi-Fi or wired, 15

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work on the same principle. 16

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They have a device that is considered as server. 17

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Now, in many cases, for example, in your home network, 18

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this server is your router. 19

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This is also referred to as an access point. 20

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Now, this router or server or access point 21

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is the only device that has access to the resource. 22

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So, none of these clients have direct access 23

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to the resource, even after connecting to the network. 24

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The only way they can access the resource 25

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is through the access point. 26

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So, let's say, for example, you're client number one 27

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and you connected to your home network 28

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over Wi-Fi or over ethernet, over a cable 29

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and then you opened your browser and you typed google.com. 30

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What happens is your computer will send the request 31

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to the access point asking for google.com. 32

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The access point has access to the resource, 33

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which is the internet in this example, 34

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so it's gonna go and look for google.com. 35

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It will receive google.com, 36

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and it'll forward that response to your computer, 37

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and as a result you will see the website 38

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loading on your browser. 39

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So if you actually go to your router at home 40

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and look at it, you'll see at the back 41

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it's connected through a cable to the wall 42

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and this is how it's getting its internet access. 43

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Therefore, it is the only device in your network 44

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that has direct access to the resource 45

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and none of your computers, 46

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none of the computers connected to the network 47

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can access the resource or can access the internet 48

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without the router, without the access point. 49

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So the only way for all of the connected clients 50

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to access the resource is to go through the router. 51

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Now, the data is transferred between clients 52

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and the access point as packets. 53

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So you can think of all of these arrows 54

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as a series of packets being transmitted 55

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between the client and the router as requests and responses. 56

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Now, in Wi-Fi networks, 57

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these packets are transmitted in the air. 58

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Therefore, if you have a wireless card 59

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and you're within range, you'll be able to capture 60

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all of these requests and responses. 61

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So, basically, you'll be able to see 62

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anything that any computer 63

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connected to the same network as you, 64

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thus on the internet, 65

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because they will have to send all of these data 66

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to the access point, 67

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and because they're sending this data in the air 68

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because you're in a WiFi network, 69

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you'll basically be able to capture 70

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these requests and responses. 71

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And you'll be able to see the URLs they visit, 72

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the usernames, the passwords they enter, the chat messages. 73

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Anything they do on the internet will be sent as packets 74

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and therefore you'll be able to capture it and analyze it. 75

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We'll talk more about that 76

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and more about how networks work 77

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as we go through the course 78

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but this is enough to get you going 79

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through the next few lectures, so that you can sniff data, 80

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analyze it and start launching 81

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some cool pre-connection attacks.