1 00:00:00,830 --> 00:00:03,830 So now we're going to talk about the application layer. 2 00:00:03,830 --> 00:00:06,495 And, up to now we've been talking about these bottom layers and we've been sort 3 00:00:06,495 --> 00:00:10,186 of working our way up. We talked about the Link Layer, the IP 4 00:00:10,186 --> 00:00:14,110 Layer and the TCP Layer. And, and, and each of these layers works 5 00:00:14,110 --> 00:00:17,297 with the other. The, the IP layer depends on a link 6 00:00:17,297 --> 00:00:21,266 layer, the TCP layer, depends on and adds value to the IP layer, and now we're 7 00:00:21,266 --> 00:00:25,550 going to talk about the application layer that is going to make use of the services 8 00:00:25,550 --> 00:00:31,470 of the TCP layer. And the services of the TCP layer are 9 00:00:31,470 --> 00:00:35,646 basically to give us a reliable, sequenced end to end stream, that can 10 00:00:35,646 --> 00:00:40,470 start in one application in one computer and end in an application in a different 11 00:00:40,470 --> 00:00:46,241 computer, and have a two way communication. 12 00:00:46,241 --> 00:00:50,993 So I can send the word Hello, Hello, from one application, and then, all kinds of 13 00:00:50,993 --> 00:00:55,889 billions of dollars of hardware, hundreds of thousands of engineers, 40 years of 14 00:00:55,889 --> 00:01:02,159 engineering design, and out comes Hello on the other end. 15 00:01:03,670 --> 00:01:07,266 And what's beautiful, and this is the beauty of the layer, of the four layer 16 00:01:07,266 --> 00:01:10,910 architecture, is we just pretend this is magic. 17 00:01:10,910 --> 00:01:17,280 This is magic. We send something and out it comes. 18 00:01:17,280 --> 00:01:19,980 With that magic available, with that billions of dollars and 40 years of 19 00:01:19,980 --> 00:01:22,745 research magic available, now what would we do? 20 00:01:22,745 --> 00:01:26,663 Right? Now what would we do with that magic if 21 00:01:26,663 --> 00:01:35,20 we had it available to us? So TCP is giving us this reliable pipe. 22 00:01:35,20 --> 00:01:37,696 We're going to think about now, we're going to ignore all the rest of it. 23 00:01:37,696 --> 00:01:39,310 Right? We're going to ignore, all this part, 24 00:01:39,310 --> 00:01:42,260 we're going to put, all we're going to say, is, we have an application on this 25 00:01:42,260 --> 00:01:46,630 end of our computer. Now remember, this is your computer. 26 00:01:46,630 --> 00:01:52,140 And say this is the server, right? So this is you, and this is the server. 27 00:01:52,140 --> 00:01:55,260 And all the software runs in it in, in every, all the software's running in your 28 00:01:55,260 --> 00:01:58,679 computer and all the software is running in the server. 29 00:02:00,80 --> 00:02:03,565 So the question is, what are we going to do between these two things, okay? 30 00:02:03,565 --> 00:02:06,650 What, how we, what, how are we going to ask for data? 31 00:02:06,650 --> 00:02:10,50 And this application is the client application. 32 00:02:10,50 --> 00:02:12,374 And this application is the server application. 33 00:02:12,374 --> 00:02:16,75 Client and server are not necessarily the same, very much the same. 34 00:02:16,75 --> 00:02:18,920 Client and server are likely very different applications. 35 00:02:18,920 --> 00:02:22,962 The client is like giving me information. And the server is responsible for giving 36 00:02:22,962 --> 00:02:27,434 giving the information to the client. So the client is often making a request, 37 00:02:27,434 --> 00:02:30,600 and then the server is making a response back. 38 00:02:30,600 --> 00:02:34,140 And so, this client server mechanism, this application to application 39 00:02:34,140 --> 00:02:37,820 communication, we could build a mail system with it. 40 00:02:37,820 --> 00:02:40,886 World wide web. Or we can stream videos much like we'll 41 00:02:40,886 --> 00:02:45,325 be streaming this lecture back and forth. But we're going to focus on the world 42 00:02:45,325 --> 00:02:49,87 wide web because it's really simple, and really elegant, and it's probably the 43 00:02:49,87 --> 00:02:53,385 easiest one to understand. And, it's the most popular. 44 00:02:53,385 --> 00:02:57,543 But there are many other protocols going on, file transfer and others, but, the 45 00:02:57,543 --> 00:03:03,69 world wide web protocol, HTTPD, is the protocol that is the most popular. 46 00:03:03,69 --> 00:03:10,430 So, the, there are two basic questions that the application layer has to solve. 47 00:03:10,430 --> 00:03:17,16 One is, which application gets the data. And this is done using a mechanism called 48 00:03:17,16 --> 00:03:21,570 ports, and ports allow a IP address, or a single computer, or a single server, to 49 00:03:21,570 --> 00:03:26,55 serve up multiple services, and then for a client to be able to dial up much like 50 00:03:26,55 --> 00:03:34,100 a telephone extension, and pick the service that they are interested in. 51 00:03:34,100 --> 00:03:38,160 Once you've connected to the service that you're interested in, like the world wide 52 00:03:38,160 --> 00:03:42,810 web service, then you need to know the protocol to talk to that. 53 00:03:42,810 --> 00:03:45,696 Ports and TCP are like a telephone extension number. 54 00:03:45,696 --> 00:03:49,11 Again, that, like I said, they, you can connect to an IP address but then you can 55 00:03:49,11 --> 00:03:53,10 connect to a port within it. And so if you think about a telephone 56 00:03:53,10 --> 00:03:57,2 number, and an extension, it's sort of a, a further refinement. 57 00:03:57,2 --> 00:04:00,530 An IP address gives us a particular server,a piece of hardware connected to 58 00:04:00,530 --> 00:04:04,338 the internet, and then a port within that tells us what application we're going to 59 00:04:04,338 --> 00:04:10,375 talk to. So, let's talk about ports and 60 00:04:10,375 --> 00:04:14,878 connections. So, if I add a server, and this kind of 61 00:04:14,878 --> 00:04:19,362 a, a arbitrary server. Here, here is a single server, 62 00:04:19,362 --> 00:04:23,584 www.umich.edu. And it has one IP address connected into 63 00:04:23,584 --> 00:04:28,360 the cloud. We can have many clients talking to it. 64 00:04:28,360 --> 00:04:32,980 And, we have many services running on this server like sending email, or 65 00:04:32,980 --> 00:04:38,293 logging in to that server, or retrieving webpages, or retrieving my mail from that 66 00:04:38,293 --> 00:04:43,620 server. And there are ports, so, incoming email 67 00:04:43,620 --> 00:04:48,820 is done generally in port 25, remote log in is 22 or 23, web servers depending on 68 00:04:48,820 --> 00:04:54,100 whether it's secure or not are 80 or 443, and, [COUGH] the personal mail box is on 69 00:04:54,100 --> 00:05:01,570 ports 109 or 110. And so these computers don't just connect 70 00:05:01,570 --> 00:05:07,450 to an IP address, but they connect to a port within an IP address. 71 00:05:07,450 --> 00:05:11,980 So some common TCP ports that we have are the ones I just mentioned. 72 00:05:11,980 --> 00:05:14,920 And you can take a look at these on the internet. 73 00:05:14,920 --> 00:05:16,584 The various ports. Okay? 74 00:05:16,584 --> 00:05:20,809 Now, once we have a connection to the web server, or to the mail server, or to the 75 00:05:20,809 --> 00:05:25,540 post office server, we have to know how to talk to it. 76 00:05:25,540 --> 00:05:27,990 And that's what's called an application protocol. 77 00:05:27,990 --> 00:05:32,330 And that is, the rules for conversation, the rules for conversing. 78 00:05:32,330 --> 00:05:35,746 So, TCP gives us this reliable connection, we now can connect to the 79 00:05:35,746 --> 00:05:39,589 server that we desire to connect to by using ports, and the question is, what 80 00:05:39,589 --> 00:05:43,127 are we going to to say across that connection, and what we say across that 81 00:05:43,127 --> 00:05:47,92 connection, who talks first, what do you send, what comes back, depends on the 82 00:05:47,92 --> 00:05:55,322 kind of server that you are talking to. We're going to play mostly with the world 83 00:05:55,322 --> 00:05:59,237 wide, the world wide web. Oops, I clicked the wrong button there, 84 00:05:59,237 --> 00:06:03,131 the world wide web server, because it's the simplest, and it's the most obvious 85 00:06:03,131 --> 00:06:07,742 as to what's going on. So the world wide web clients, and the 86 00:06:07,742 --> 00:06:12,20 world wide, which are otherwise known as browsers, the world wide web clients, and 87 00:06:12,20 --> 00:06:17,620 the world wide web servers communicate using a protocol called HTTP. 88 00:06:17,620 --> 00:06:22,420 As a matter of fact, if you look at the top of your URL it's http://, something, 89 00:06:22,420 --> 00:06:27,43 dot dot dot, right? And [COUGH], and so basically, there is a 90 00:06:27,43 --> 00:06:31,20 specification for how this is done. So when they wrote down, I'm going to 91 00:06:31,20 --> 00:06:34,650 write the first web browser and the first web server, they also wrote a document 92 00:06:34,650 --> 00:06:40,226 about how that piece of software would talk to this other piece of software. 93 00:06:40,226 --> 00:06:43,450 And the, and it's a very simple concept, http has a protocol where you make a 94 00:06:43,450 --> 00:06:47,270 connection to the, from the client to the server. 95 00:06:47,270 --> 00:06:50,660 The client requests a document. The server feeds out the document. 96 00:06:50,660 --> 00:06:52,700 And then the connection is dropped. Okay? 97 00:06:52,700 --> 00:06:55,420 So it's very simple. We'll actually simulate this. 98 00:06:55,420 --> 00:07:00,172 This is called the HTTP request response cycle. 99 00:07:00,172 --> 00:07:03,193 Okay? And so the way it works, is, you're in a 100 00:07:03,193 --> 00:07:07,333 browser, and you click on a link, the browser's an application, it's the 101 00:07:07,333 --> 00:07:11,956 client, running on your computer, so, so this is kind of your computer down here, 102 00:07:11,956 --> 00:07:17,181 okay. You click on a link, then the browser 103 00:07:17,181 --> 00:07:23,310 makers a connection to the web server and sends a request to, for the document. 104 00:07:23,310 --> 00:07:27,464 The web server looks up, does whatever, and sends the document back, and then the 105 00:07:27,464 --> 00:07:31,590 document is displayed on your screen. Okay. 106 00:07:31,590 --> 00:07:37,680 So, let me show you sort of how this works with a web browser. 107 00:07:37,680 --> 00:07:42,774 So here is a canonical webpage. So here's a browser, here's the URL that 108 00:07:42,774 --> 00:07:46,950 I went and got, you can get this URL as well, you can even look at the source. 109 00:07:46,950 --> 00:07:51,263 So if you look at this source there is [COUGH] my HTML. 110 00:07:51,263 --> 00:07:54,292 But one of the things that's in this source is a link. 111 00:07:54,292 --> 00:07:57,773 And if I hover over top of this link, whoops, I gotta go like that to hover 112 00:07:57,773 --> 00:08:01,678 over the top of the link. You can see, at the bottom of my screen, 113 00:08:01,678 --> 00:08:05,387 you can see it's going to tell you that we're about to go retrieve page2.htm. 114 00:08:05,387 --> 00:08:12,640 Now, this browser is running on my laptop. 115 00:08:12,640 --> 00:08:16,990 It is a web client. It is an HTTP client. 116 00:08:16,990 --> 00:08:21,590 And I'm about to click on this piece of software running on my computer. 117 00:08:21,590 --> 00:08:25,490 And then it is going to make a connection out the back of it, retrieve a document 118 00:08:25,490 --> 00:08:29,740 and then show me the other document. So it's going to happen real fast. 119 00:08:29,740 --> 00:08:33,824 I'll click on second page. It requested, and got a document back, 120 00:08:33,824 --> 00:08:37,529 and showed me the document. So that's the contents of the second 121 00:08:37,529 --> 00:08:41,934 document, okay. And so that is the request response cycle 122 00:08:41,934 --> 00:08:47,394 that is triggered, that is triggered by me making a click somewhere in my 123 00:08:47,394 --> 00:08:51,935 browser. The, the browser sees the click, it opens 124 00:08:51,935 --> 00:08:54,639 a connection, this is sort of the internet over here, it makes a 125 00:08:54,639 --> 00:08:57,915 connection, requests a document, the document comes back, and then the new 126 00:08:57,915 --> 00:09:02,152 document is displayed. The request, response cycle. 127 00:09:02,152 --> 00:09:06,189 Click, request, response, display. Click, request, response, display. 128 00:09:06,189 --> 00:09:11,697 So let's take a look in some more detail as to what's really going on here. 129 00:09:11,697 --> 00:09:16,449 So, the command that is being sent up to the server, across this connection, and 130 00:09:16,449 --> 00:09:21,710 remember that this part here's the internet right there. 131 00:09:21,710 --> 00:09:25,970 The command is a get command. And the document is based on the URL I 132 00:09:25,970 --> 00:09:30,594 clicked on that the browser knows about, and says get /page2.html, and what comes 133 00:09:30,594 --> 00:09:35,938 back is HTML. And that is a markup language that 134 00:09:35,938 --> 00:09:40,890 describes how this doc, how this page is supposed to be shown. 135 00:09:40,890 --> 00:09:45,840 So let's say that we wanted some more detail on how this really worked, right. 136 00:09:45,840 --> 00:09:49,195 Let's say that we want to write a web browser and we want to be a good citizen 137 00:09:49,195 --> 00:09:53,330 and we want to talk properly to the the web. 138 00:09:53,330 --> 00:09:57,750 Well, we would go back to the IETF, the Internet Engineering Task Force, and we 139 00:09:57,750 --> 00:10:02,102 would go grab the document that says hey, if you want to write a browser, this is 140 00:10:02,102 --> 00:10:06,834 what you do. This is what you do if you want to write 141 00:10:06,834 --> 00:10:10,340 a browser. You can go grab RFC 1945. 142 00:10:10,340 --> 00:10:14,40 Which is the hypertext transport protocol version 1.0. 143 00:10:14,40 --> 00:10:17,462 Now I'm sure there's more complex superseeded versions of it, but if we 144 00:10:17,462 --> 00:10:20,826 read it, and read it, and read it, we spent a lot of time, we'd get down to 145 00:10:20,826 --> 00:10:24,596 section 5.1.2, and it would say, if you are making a request for a document this 146 00:10:24,596 --> 00:10:30,970 is the request line. It has the letters G E T, followed by a 147 00:10:30,970 --> 00:10:35,41 space, followed by the URL you're looking for, followed by a space, followed by the 148 00:10:35,41 --> 00:10:38,933 version, okay? So that is the rule. 149 00:10:38,933 --> 00:10:43,585 That is what you're supposed to send down this connection. 150 00:10:43,585 --> 00:10:46,610 It'll give us some more examples on page 24. 151 00:10:46,610 --> 00:10:51,240 And so, we could read all this, and we could write a web browser. 152 00:10:51,240 --> 00:10:54,488 But what we're going to do, is we're going to fake being a web browser, we're 153 00:10:54,488 --> 00:10:57,420 going to cheat. We're going to hack it. 154 00:10:57,420 --> 00:10:59,80 We're going to pretend to be a web browser. 155 00:10:59,80 --> 00:11:02,516 We're going to send the commands, to the web browser. 156 00:11:02,516 --> 00:11:06,360 Now, I'm going to do this on a Macintosh, you could also do it on Windows, if you 157 00:11:06,360 --> 00:11:11,19 installed Telnet Client, okay. So the key is you install a Telnet 158 00:11:11,19 --> 00:11:13,970 client. Now most people would say that Relnet is 159 00:11:13,970 --> 00:11:17,750 insecure, and it is, it's a very old protocol, because all it does is it opens 160 00:11:17,750 --> 00:11:21,410 a TCP connection to a host on a port that I specify, and whatever I type goes 161 00:11:21,410 --> 00:11:27,298 across that TCP connection. So it's a great way to hack, especially 162 00:11:27,298 --> 00:11:31,811 older, less secure protocols. So because HTTP is generally a public 163 00:11:31,811 --> 00:11:35,532 protocol, it's not really highly protected, so it's much simpler to hack 164 00:11:35,532 --> 00:11:38,633 it. Hacking secure protocols is, requires 165 00:11:38,633 --> 00:11:41,230 writing software rather than typing commands. 166 00:11:41,230 --> 00:11:46,590 So if you're on windows you have to install Telnet, T-E-L-N-E-T. 167 00:11:46,590 --> 00:11:49,900 So what I'm going to show you in a second, is I'm going to show you hacking. 168 00:11:49,900 --> 00:11:50,439 And I'm going to telnet to www.drchuck.com, port 80. 169 00:11:50,439 --> 00:11:57,4 What I'm saying is, connect me to this server on the internet, and connect me to 170 00:11:57,4 --> 00:12:02,761 port 80, because I want to do HTTP connections, and then I will send one 171 00:12:02,761 --> 00:12:08,450 command. I'm going to send that command. 172 00:12:08,450 --> 00:12:10,642 And then the web server will give me back the page. 173 00:12:10,642 --> 00:12:15,53 Okay? It's probably easier for me to just do 174 00:12:15,53 --> 00:12:19,510 it. So let's take a look. 175 00:12:19,510 --> 00:12:23,974 I am going to simulate what the web browser does when it's requesting, well 176 00:12:23,974 --> 00:12:28,654 actually, we'll go to the second page, and when it's requesting the first page 177 00:12:28,654 --> 00:12:33,490 it's doing a get for page one. Okay. 178 00:12:33,490 --> 00:12:42,380 So that's what we're going to do, except now we're going to do it in a terminal. 179 00:12:42,380 --> 00:12:46,278 So I'm going to type telnet, whoops, I always type this wrong. 180 00:12:46,278 --> 00:12:52,148 T-E-L-N-E-T, www.dr-chuck.com, port 80. Okay. 181 00:12:52,148 --> 00:12:53,923 So now I am connected to the webserver on dr-chuck.com. 182 00:12:53,923 --> 00:13:19,140 I could, for example, type yo, what is up, dude. 183 00:13:19,140 --> 00:13:23,40 Now that would suggest I have not read the protocol specification for the HTTP 184 00:13:23,40 --> 00:13:28,270 protocol, so I do not know that I'm supposed to type the word Get here. 185 00:13:28,270 --> 00:13:36,340 I'm going to type yo, what is up Dude. And it goes, you are not from my country. 186 00:13:36,340 --> 00:13:39,350 You are not from my planet. I do not know what you said. 187 00:13:39,350 --> 00:13:43,254 Of course that, the way web servers are saying this, is they're saying bad 188 00:13:43,254 --> 00:13:46,383 request. Your browser sent a request that this 189 00:13:46,383 --> 00:13:50,15 server could not understand. It is, the request header is missing a 190 00:13:50,15 --> 00:13:53,735 colon separator. You do not comply, go away. 191 00:13:53,735 --> 00:13:58,630 But we did talk. It just told us that whatever we were 192 00:13:58,630 --> 00:14:03,334 saying is gibberish to it. And that's okay, because we have read the 193 00:14:03,334 --> 00:14:08,210 document, and so we can do it. So let's do it. 194 00:14:08,210 --> 00:14:11,726 So now I'm going to do is telnet to dr-chuck.com on port 80. 195 00:14:11,726 --> 00:14:16,325 Go to dr-chuck, hook onto port 80, so we can talk to the web server, and now I am 196 00:14:16,325 --> 00:14:21,202 going to behave. I read the specification. 197 00:14:21,202 --> 00:14:28,799 I'm going to type G-E-T, get, space, one space, http://www.dr-chuck.com/page1.htm, 198 00:14:28,799 --> 00:14:35,433 HTTP, space 1, dot, I think there's a slash there, whoops, oh no, no, no, get 199 00:14:35,433 --> 00:14:41,650 it right, get it right. Slash 1 dot 0. 200 00:14:41,650 --> 00:14:46,80 I think I got that right. So that is what I'm supposed to type if I 201 00:14:46,80 --> 00:14:50,770 am a real browser. Now I have to actually type another new 202 00:14:50,770 --> 00:14:58,320 line, so I'll type another new line, and now whoa, oh, I gave it the wrong page. 203 00:14:58,320 --> 00:15:01,770 Look, look, look, look, look. I wanted to do, I told it to get 204 00:15:01,770 --> 00:15:05,140 page.htm. So let's do it again, do it again. 205 00:15:05,140 --> 00:15:08,650 I'm not very good at this, my browser is much better at it. 206 00:15:08,650 --> 00:15:19,300 So I type get http://www.dr-chuck.com/page1.htm, space, 207 00:15:19,300 --> 00:15:24,748 HTTP/1.0. I believe that's it. 208 00:15:24,748 --> 00:15:32,410 Let's hope I got it right this time. And then another enter, and then another 209 00:15:32,410 --> 00:15:32,700 enter. Yay, I got it. 210 00:15:32,700 --> 00:15:38,250 So this time, I'd type, you know, I'd type this, then I'd type this. 211 00:15:38,250 --> 00:15:42,936 Now it gave me some header information, it's saying things like 200 okay means I 212 00:15:42,936 --> 00:15:48,660 like you what the time is, when this file was last modified. 213 00:15:48,660 --> 00:15:52,880 It's an HTML file and it actually shows me the HTML text. 214 00:15:52,880 --> 00:16:00,126 And so we have just hacked, a web server. You can do this to like facebook.com, and 215 00:16:00,126 --> 00:16:02,694 do a Get. If you get the right thing, it will give 216 00:16:02,694 --> 00:16:05,249 you stuff. You can go to various sites, you can fake 217 00:16:05,249 --> 00:16:07,622 browsers. Now, you're only going to get so far, 218 00:16:07,622 --> 00:16:10,672 because at some point, these servers know that you're not a browser, because a 219 00:16:10,672 --> 00:16:15,80 browser actually sends a little more stuff than what we just sent. 220 00:16:15,80 --> 00:16:17,190 But, you get the picture. Okay. 221 00:16:17,190 --> 00:16:22,41 It's a protocol where we have rules, and if we type the right thing, if we type 222 00:16:22,41 --> 00:16:26,584 the right thing, we know what the specification tells us to type, we are 223 00:16:26,584 --> 00:16:32,682 rewarded, with the information on that server. 224 00:16:32,682 --> 00:16:37,128 If we comply with the server's request, we can talk to it. 225 00:16:37,128 --> 00:16:40,264 If we know how to talk, if we know what port to talk to, and we know what 226 00:16:40,264 --> 00:16:43,624 protocol to talk to that port we can write a client that meets the needs of 227 00:16:43,624 --> 00:16:51,376 that server and extract the data. So this is, I like, I like command lines, 228 00:16:51,376 --> 00:16:56,50 I like sort of old school user interfaces, and this is a scene from one 229 00:16:56,50 --> 00:17:01,520 of the Matrix movies, that you may recall. 230 00:17:01,520 --> 00:17:04,280 I can't put it in here because of copyright re, requirements. 231 00:17:04,280 --> 00:17:07,118 I might have a URL, or maybe students will come up with a URL. 232 00:17:07,118 --> 00:17:09,590 You can probably search for the Trinity hacking scene. 233 00:17:09,590 --> 00:17:12,324 People put it up and then it gets taken down and someone else puts it up. 234 00:17:12,324 --> 00:17:15,540 So let me tell you a little story about this scene. 235 00:17:15,540 --> 00:17:19,252 This scene was actually written by a former student of mine, who worked on all 236 00:17:19,252 --> 00:17:22,960 three Matrix movies doing IT work on the movies. 237 00:17:22,960 --> 00:17:27,316 And they were in Australia shooting the, the, the three, the second set of three 238 00:17:27,316 --> 00:17:31,954 movies, and he saw this scene. And the scene was supposed to use a 239 00:17:31,954 --> 00:17:35,666 Minority Report style way for her to hack into the, the power grid, and shut it 240 00:17:35,666 --> 00:17:39,322 down. And he said, that's not the way that you 241 00:17:39,322 --> 00:17:42,50 hack into computers. [COUGH]. 242 00:17:42,50 --> 00:17:46,520 All good hackers use a text based interfa, interface, some old thing. 243 00:17:46,520 --> 00:17:51,272 And that's a throwback interface. So the Wachowski brothers told him 244 00:17:51,272 --> 00:17:55,110 rewrite it. So he actually downloaded the exact 245 00:17:55,110 --> 00:17:59,240 hacking software, its called Nmap, which stands for network map. 246 00:17:59,240 --> 00:18:03,108 It is mapping the ports. Its, probes the ports and sees whats on 247 00:18:03,108 --> 00:18:05,538 the ports. See what version of software's on each of 248 00:18:05,538 --> 00:18:08,785 the ports. Figures out what the, what the weaknesses 249 00:18:08,785 --> 00:18:13,450 of those things are, and even automatically exploits the weaknesses. 250 00:18:13,450 --> 00:18:17,14 So he wrote a script that downloaded this thing that automatically breaks into 251 00:18:17,14 --> 00:18:20,50 computers. By the way, the good guys use this and 252 00:18:20,50 --> 00:18:23,800 the bad guys use this same thing. The good guys use it to test all of the 253 00:18:23,800 --> 00:18:26,595 computers on their campus and make sure that they are okay, and the bad guys use 254 00:18:26,595 --> 00:18:30,846 to break into the ones that the good guys aren't smart enough to fix. 255 00:18:30,846 --> 00:18:34,70 And so [COUGH], this was kind of cool, and, and the people who wrote nmap were 256 00:18:34,70 --> 00:18:37,262 really quite amazed when they saw the movie. 257 00:18:37,262 --> 00:18:40,120 They even figured out what version it was and things like that. 258 00:18:40,120 --> 00:18:45,480 And so it actually triggered a series of follow on scenes that use actual real 259 00:18:45,480 --> 00:18:52,80 hacking software nmap hacking software. So, I don't know if we've got a URL for 260 00:18:52,80 --> 00:18:56,172 this or not, whatever URL I come up with even the one in the n, nmap people come 261 00:18:56,172 --> 00:19:00,16 up with, whatever it is goes away because of copyright, but you can find it, 262 00:19:00,16 --> 00:19:06,816 because someone always puts it back up. So, okay, so, maybe you can go and maybe 263 00:19:06,816 --> 00:19:10,226 the nmap people will know it or maybe you just have to search for the Trinity 264 00:19:10,226 --> 00:19:15,414 hacking scene. So you can use telnet and you can hack, 265 00:19:15,414 --> 00:19:21,353 legitimately hack a web server. So, [COUGH] basically the application 266 00:19:21,353 --> 00:19:24,917 layer is a rich place, and there's lots of things that happen in the application 267 00:19:24,917 --> 00:19:28,280 layer. We have this pipe abstraction, it's 268 00:19:28,280 --> 00:19:31,348 kind of like a, a string with two tin cans, and we can shout into one end and 269 00:19:31,348 --> 00:19:36,978 stuff comes out the other end. later we'll talk about adding security to 270 00:19:36,978 --> 00:19:41,796 that, and we use these port numbers to allow to, multiple different servers, or 271 00:19:41,796 --> 00:19:47,650 services on a computer that we can connect to. 272 00:19:47,650 --> 00:19:51,290 [COUGH] So we kind of now reached the top of the architecture of the internet. 273 00:19:51,290 --> 00:19:54,700 We've talked about ethernet, the link layer, the fiber and all the diverse 274 00:19:54,700 --> 00:19:58,594 wireless, all of the wonderful things that happen there. 275 00:19:58,594 --> 00:20:03,14 The internet work layer, which is this kind of geographical hopping thing that's 276 00:20:03,14 --> 00:20:06,28 unreliable. The TCP layer that retransmits 277 00:20:06,28 --> 00:20:10,448 automatically if necessary. And then the application layer, which is 278 00:20:10,448 --> 00:20:15,245 what we do with all this networks. [COUGH] It's really impressive that this 279 00:20:15,245 --> 00:20:20,171 came out of research work from the 1970s. And that most of the architectures that 280 00:20:20,171 --> 00:20:24,727 were really present, most of the ideas of the architecture from the 70s are really 281 00:20:24,727 --> 00:20:33,57 still present with us today. [COUGH] As the NSF net came out, these 282 00:20:33,57 --> 00:20:37,345 architectures evolved a little bit, the last few tweaks, and there have been 283 00:20:37,345 --> 00:20:41,365 tweaks going on ever since, but the, really the last few critical tweaks 284 00:20:41,365 --> 00:20:47,921 happened in the late 1980s. The [COUGH] the number of web hosts or 285 00:20:47,921 --> 00:20:52,16 the number of hosts on the internet goes from six in 1969, to sort of a billion in 286 00:20:52,16 --> 00:20:56,371 2011. And, and it's pretty impressive that 287 00:20:56,371 --> 00:21:00,915 roughly the same architecture that was designed with six computers is still 288 00:21:00,915 --> 00:21:05,672 mostly functioning in a, in mostly the same patterns, all these years later with 289 00:21:05,672 --> 00:21:11,908 bill, billions of computers. And so, if you start looking at the 290 00:21:11,908 --> 00:21:16,396 network now, it almost looks like a live creature with veins, and nerves, and it 291 00:21:16,396 --> 00:21:20,952 sort of almost pulses, and you see things like, you can search on the internet for 292 00:21:20,952 --> 00:21:25,440 how the internet reacted to Hurricane Sandy, when, like, New York City was just 293 00:21:25,440 --> 00:21:33,270 like shut off for three days. The internet just kind of like, routed 294 00:21:33,270 --> 00:21:36,200 around it. Yeah a lot of stuff went across the 295 00:21:36,200 --> 00:21:40,40 Atlantic ocean from New York City and yeah, it found different paths, and you 296 00:21:40,40 --> 00:21:44,120 know, yeah, New York was down, but the rest of it wasn't, in many ways pretty 297 00:21:44,120 --> 00:21:49,182 amazing. And, we certainly see other situations 298 00:21:49,182 --> 00:21:52,542 where governments try to shut the internet down by going into the server 299 00:21:52,542 --> 00:21:56,238 rooms, and shutting off, you know, what they think is the only connections, but 300 00:21:56,238 --> 00:22:02,942 then more connections pop up. And so it's, it's very much a almost a 301 00:22:02,942 --> 00:22:06,930 living thing. It's billions of computers, and hundreds 302 00:22:06,930 --> 00:22:10,745 of thousands of routers. And, and, it's, hundreds of millions of 303 00:22:10,745 --> 00:22:13,790 simultaneous connections going on all the time. 304 00:22:13,790 --> 00:22:17,868 Including the one we're doing right now, probably. 305 00:22:17,868 --> 00:22:23,97 And, it's trillions of bytes a day to moving across, and it's, it's, it's not 306 00:22:23,97 --> 00:22:28,996 perfect, but it kind of works. You can think of it as like, the largest, 307 00:22:28,996 --> 00:22:33,398 engi-collective, engineering thing that we've done together as humanity, we built 308 00:22:33,398 --> 00:22:36,814 this. It's all one thing, and yet it's so many 309 00:22:36,814 --> 00:22:39,960 different pieces. And we just kind of keep, gluing them 310 00:22:39,960 --> 00:22:43,76 together, and gluing more things on more things. 311 00:22:43,76 --> 00:22:46,470 And it was, it really was created almost like life itself. 312 00:22:46,470 --> 00:22:49,780 It's very organic. It's designed to heal itself, rather than 313 00:22:49,780 --> 00:22:52,770 be perfect. Because things that try to be perfect are 314 00:22:52,770 --> 00:22:57,322 fragile, and they break too easily. But things that are designed to heal, can 315 00:22:57,322 --> 00:22:59,970 heal. And you're never perfectly correct. 316 00:22:59,970 --> 00:23:02,730 You're never all the way up, and you're never all the way down. 317 00:23:02,730 --> 00:23:05,632 And so that's what's interesting about the internet. 318 00:23:05,632 --> 00:23:09,615 Oops, went the wrong way. And so, we kind of come to the end of 319 00:23:09,615 --> 00:23:13,580 this, where we started out with like machines, and pulleys and gears, and 320 00:23:13,580 --> 00:23:17,805 spraying oil at [UNKNOWN], and, typing a few characters on a keyboard, to this 321 00:23:17,805 --> 00:23:21,835 thing, where we, sort of just take for granted that we can watch basketball 322 00:23:21,835 --> 00:23:29,877 anywhere on the planet, just with a couple of swipes of the, of the key. 323 00:23:29,877 --> 00:23:34,842 And in a sense, it's just that same human urge to communicate at a distance. 324 00:23:34,842 --> 00:23:40,57 And so the last thing that I'll close with is another video from Van Jacobsom. 325 00:23:40,57 --> 00:23:44,446 Now, this is about a technique he calls Content Centric Networking. 326 00:23:45,830 --> 00:23:49,430 And not everybody agrees with Van Jacobson on this. 327 00:23:49,430 --> 00:23:53,6 You can ask people and they'll say it's a good idea. 328 00:23:53,6 --> 00:23:57,296 That, I don't present this as the future, I present this more to get you thinking 329 00:23:57,296 --> 00:24:02,620 that there is a future that might be different than the present. 330 00:24:02,620 --> 00:24:08,500 That what I just told you, that seems, seems like oh, it's perfect. 331 00:24:08,500 --> 00:24:12,850 And the, and when, and Vint Cerf in 1969, he figured this out. 332 00:24:12,850 --> 00:24:16,225 And, [SOUND] , it was the perfect thing, right? 333 00:24:16,225 --> 00:24:19,210 And, the answer is, it might not be. And we, as engineers, and we as the 334 00:24:19,210 --> 00:24:22,510 people of the internet, we must understand that, in 20 years, it might be 335 00:24:22,510 --> 00:24:26,49 all different. Because, 20 years ago, it was all 336 00:24:26,49 --> 00:24:28,366 different. And 30 years before that, it was 337 00:24:28,366 --> 00:24:31,290 different yet again. And so nothing's perfect. 338 00:24:31,290 --> 00:24:34,995 And so we should never be complacent, and assume that what we have is trivial or 339 00:24:34,995 --> 00:24:39,970 perfect, or even the right answer. So we should continue to question. 340 00:24:39,970 --> 00:24:43,588 And so it's really interesting to hear, again, from Jan Jacobson, who sort of did 341 00:24:43,588 --> 00:24:46,990 this great innovation in 1987 that saved us, and yet he thinks that these are 342 00:24:46,990 --> 00:24:51,699 issues, and they're issues that need to be saved again. 343 00:24:51,699 --> 00:24:55,838 And I think, in many ways, he's right. The question is not so much whether he's 344 00:24:55,838 --> 00:24:59,590 right or wrong, the question is, what will the ultimate solution that we pick 345 00:24:59,590 --> 00:25:03,574 be produced. So, so, take a look at Van Jacobson, and 346 00:25:03,574 --> 00:25:07,474 what he can, what he is thinking about as terms of the issues in the future, that 347 00:25:07,474 --> 00:25:13,633 we're going to need to solve, when he talks about content centered networking.