WEBVTT 1 00:00:00.120 --> 00:00:02.799 You know, when we sit at a desk and just 2 00:00:02.919 --> 00:00:06.000 drag a file from our screen to a coworker's folder, 3 00:00:06.879 --> 00:00:09.839 there's this, I don't know, this expectation of magic. 4 00:00:10.000 --> 00:00:12.160 Oh totally. It's like teleportation, right. 5 00:00:12.160 --> 00:00:15.679 You drag, you drop, and poof, the file is just there. 6 00:00:15.880 --> 00:00:20.480 Yeah. It feels completely instantaneous and clean and totally invisible. 7 00:00:20.960 --> 00:00:22.679 We just take for granted, you know, we expect the 8 00:00:22.719 --> 00:00:25.879 technology to just work without ever really thinking about the 9 00:00:25.920 --> 00:00:28.120 crazy mechanics underneath the keyboard exactly. 10 00:00:28.359 --> 00:00:30.600 But then you actually look at the physical reality of 11 00:00:30.640 --> 00:00:35.240 a network and that whole teleportation illusion just shatters completely. 12 00:00:35.399 --> 00:00:38.000 It really does, because what we're actually looking at is 13 00:00:38.039 --> 00:00:42.600 this wild landscape of electrical pulses and hexodecimal codes. It's 14 00:00:42.640 --> 00:00:46.960 this highly choreographed system of invisible traffic that is honestly 15 00:00:47.039 --> 00:00:48.759 just mind boggling when you dig into it. 16 00:00:49.159 --> 00:00:52.719 I like to call it the absolute definition of structured chaos. 17 00:00:52.320 --> 00:00:54.600 Which is exactly why today's deep dive is going to 18 00:00:54.640 --> 00:00:57.920 demystify that chaos. We are taking you on a journey 19 00:00:57.960 --> 00:01:02.280 down the invisible hyperfast high way that connects our computers. 20 00:01:01.840 --> 00:01:05.680 And we're using Mike Meyer's Comtia network plus Certification Guide 21 00:01:05.760 --> 00:01:07.120 as our map for this one. 22 00:01:07.359 --> 00:01:09.959 Right, the mission here is to figure out how data 23 00:01:10.040 --> 00:01:13.480 actually travels. So let's look at a scenario the source 24 00:01:13.519 --> 00:01:18.239 sets up. Imagine two co workers, Janelle and Dana. Okay, 25 00:01:18.560 --> 00:01:22.280 they work in administration at this fictional company called mhtechad 26 00:01:22.760 --> 00:01:26.079 and Janelle has just finished writing a massive new employee 27 00:01:26.079 --> 00:01:30.040 handbook in Microsoft Word and she wants Dana to check 28 00:01:30.079 --> 00:01:31.040 it for accuracy. 29 00:01:31.280 --> 00:01:33.719 A classic office setup, I mean, Janelle needs to get 30 00:01:33.719 --> 00:01:36.159 a really large digital file to another person in the 31 00:01:36.239 --> 00:01:37.120 exact same building. 32 00:01:37.200 --> 00:01:39.879 Now, Janelle could just save that document to a flash drive, 33 00:01:40.200 --> 00:01:42.599 stand up, and physically walk it over to Dana's desk. 34 00:01:43.159 --> 00:01:45.000 The old school sneakernet. 35 00:01:44.519 --> 00:01:48.079 Mess is sneakernet, right, which technically works, but it kind 36 00:01:48.079 --> 00:01:51.239 of defeats the entire purpose of having computers wired together 37 00:01:51.319 --> 00:01:52.319 in a modern office. 38 00:01:52.480 --> 00:01:54.480 Right. Yeah, absolutely, it's terribly inefficient. 39 00:01:54.599 --> 00:01:56.959 So instead, without Eve turning around in her chair, she 40 00:01:57.120 --> 00:01:59.480 drags the file across her screen and sends it over 41 00:01:59.519 --> 00:02:02.680 the network. But and this is the big question, how 42 00:02:02.680 --> 00:02:06.239 does that file actually travel from Janelle's desk to Dana's 43 00:02:06.239 --> 00:02:07.840 desk without magic? 44 00:02:08.000 --> 00:02:09.680 That is the million dollar question. 45 00:02:10.039 --> 00:02:12.319 Well, by the end of this deep dive. You will 46 00:02:12.360 --> 00:02:15.159 never look at a plugged in computer the exact same way. 47 00:02:15.199 --> 00:02:18.479 Again, I promise you won't, because to understand how Janelle's 48 00:02:18.520 --> 00:02:21.319 file moves, we can't just stare at the jumble of 49 00:02:21.439 --> 00:02:24.800 cables under the desk or the software on her monitor. 50 00:02:25.199 --> 00:02:27.479 We first have to look at the architectural blueprint that 51 00:02:27.560 --> 00:02:31.759 makes the whole system even possible. The source actually spends 52 00:02:31.800 --> 00:02:34.479 a lot of time on this concept of a network model. 53 00:02:34.560 --> 00:02:37.639 Okay, let's unpack this. Yeah, when we hear the word model, 54 00:02:37.960 --> 00:02:40.960 we usually think of like a plastic model airplane, right, 55 00:02:41.120 --> 00:02:43.599 like a toy. Yeah, it has the wings, the tail, 56 00:02:43.719 --> 00:02:48.719 the cockpit, but it intentionally omits the incredibly complex internal 57 00:02:48.759 --> 00:02:53.080 combustion engine exactly. Or think of a computer model predicting 58 00:02:53.120 --> 00:02:58.680 the weather. It takes this overwhelmingly chaotic reality global wind patterns, 59 00:02:58.759 --> 00:03:05.159 ocean temperatures, bemetric pressure, and simplifies it into digestible, predictable parts. 60 00:03:05.360 --> 00:03:08.039 And a network model does the exact same thing for 61 00:03:08.120 --> 00:03:11.680 the overwhelming complexity of computer networking. It breaks the entire 62 00:03:11.719 --> 00:03:14.159 process down into discrete individual steps. 63 00:03:13.879 --> 00:03:15.759 Which makes it something we can actually wrap our heads. 64 00:03:15.560 --> 00:03:18.719 Around, exactly. And the gold standard we're looking at today 65 00:03:19.159 --> 00:03:23.240 is called the OSI seven layer model OSI. Yeah. OSI 66 00:03:23.319 --> 00:03:26.719 stands for Open Systems Interconnection, and it was created by 67 00:03:26.759 --> 00:03:29.599 the International Organization for Standardization. 68 00:03:28.919 --> 00:03:31.680 Which gives us seven specific layers to get from a 69 00:03:31.680 --> 00:03:34.199 physical cable all the way up to the application you 70 00:03:34.240 --> 00:03:38.639 are actually clicking on. So, starting from the bottom, layer 71 00:03:38.639 --> 00:03:41.319 one is the physical layer, then layer two is data link, 72 00:03:41.599 --> 00:03:44.919 Layer three is network, Layer four's transport, layer five is session, 73 00:03:45.039 --> 00:03:48.159 layer six is presentation, and layer seven is application. 74 00:03:48.360 --> 00:03:49.919 That's flot to remember it is. 75 00:03:50.199 --> 00:03:54.000 But the source gives us a classic technomonic to remember 76 00:03:54.039 --> 00:03:55.719 it from bottom to top. 77 00:03:56.719 --> 00:03:58.599 Please do not throw sausage pizza away. 78 00:03:58.680 --> 00:04:00.960 I love that it sounds silly, but I mean network 79 00:04:00.960 --> 00:04:03.960 engineers use that inemonic constantly to keep the hierarchy straight. 80 00:04:04.280 --> 00:04:05.719 The thing that really stood out to me in the 81 00:04:05.719 --> 00:04:09.240 text is how the OSI model encourages modular design. 82 00:04:09.400 --> 00:04:10.000 Oh yeah. 83 00:04:10.120 --> 00:04:13.039 Think of it like an automobile assembly line. The person 84 00:04:13.080 --> 00:04:15.199 whose job it is to paint the car doesn't care 85 00:04:15.199 --> 00:04:16.680 about the person putting the doors. 86 00:04:16.480 --> 00:04:19.560 On, not at all. He just expects the assembly line 87 00:04:19.680 --> 00:04:22.360 to hand him a car with doors ready to be painted. 88 00:04:23.120 --> 00:04:26.800 Each layer blindly trusts that the other layers are doing 89 00:04:26.839 --> 00:04:29.120 their specific job perfectly. 90 00:04:28.959 --> 00:04:32.079 And that modularity is just vital for troubleshooting. Like if 91 00:04:32.120 --> 00:04:36.240 a backo outside accidentally cuts the main fiber optic cable 92 00:04:36.279 --> 00:04:36.480 to the. 93 00:04:36.480 --> 00:04:38.800 Building, which happens way more often than it should. 94 00:04:38.959 --> 00:04:43.199 Right. If that happens layer one, the physical layer's broken. 95 00:04:43.879 --> 00:04:47.240 But the software developers who built Microsoft Word at layer seven, 96 00:04:47.759 --> 00:04:50.000 they don't have to rewrite their entire application to fix 97 00:04:50.000 --> 00:04:50.480 the problem. 98 00:04:50.519 --> 00:04:51.839 Oh wow, yeah, that makes sense. 99 00:04:51.879 --> 00:04:53.720 Gives way for someone to plug in a new cable 100 00:04:54.120 --> 00:04:57.639 providing that structure was completely revolutionary. If we look at 101 00:04:57.639 --> 00:05:01.439 the early days of networking, before models like OSI, one 102 00:05:01.519 --> 00:05:03.600 manufacturer made absolutely everything. 103 00:05:03.279 --> 00:05:04.560 You mean, like hardware and software. 104 00:05:04.680 --> 00:05:08.439 Everything you bought a complete package, hardware, software, cables. All 105 00:05:08.480 --> 00:05:12.040 of it was proprietary, like a walled garden completely. An 106 00:05:12.040 --> 00:05:16.240 IBM network worked beautifully, but it only spoke IBM. An 107 00:05:16.240 --> 00:05:18.600 Apple network only spoke Apple. 108 00:05:18.360 --> 00:05:19.639 So they couldn't talk to each other. 109 00:05:19.959 --> 00:05:24.000 It made it incredibly difficult, almost impossible really, for computers 110 00:05:24.040 --> 00:05:26.480 from different manufacturers to actually talk to each other in 111 00:05:26.560 --> 00:05:31.199 the same office. The OSI model became the universal translator. 112 00:05:31.800 --> 00:05:34.519 It allowed developer to focus on just building a great 113 00:05:34.519 --> 00:05:37.279 network card or just building a great web browser, knowing 114 00:05:37.319 --> 00:05:39.399 it would interface perfectly with the rest of the stack. 115 00:05:39.600 --> 00:05:41.839 So let's walk down those stairs and build this blueprint. 116 00:05:42.240 --> 00:05:45.680 Let's trace Janelle's file starting at the very bottom layer one, 117 00:05:46.240 --> 00:05:49.839 the physical realm, the foundation, because every blueprint has to 118 00:05:49.839 --> 00:05:53.439 be built on a tangible foundation. The journey of Janelle's 119 00:05:53.439 --> 00:05:55.800 file literally starts in the physical world. 120 00:05:55.959 --> 00:05:59.839 This is the hardware, the cabling, and the central connection box. 121 00:06:00.480 --> 00:06:03.399 Most modern office networks use a specific type of cable 122 00:06:03.439 --> 00:06:07.040 called unshielded twisted pair or UTP YOUUGP rate. Inside that 123 00:06:07.120 --> 00:06:10.439 plastic cable casing are four pairs of tiny copper wires. 124 00:06:10.759 --> 00:06:13.639 Twist it together in a very specific way to prevent 125 00:06:13.800 --> 00:06:18.120 electromagnetic interference, and those wires are what actually transmit and 126 00:06:18.199 --> 00:06:19.040 receive data. 127 00:06:19.160 --> 00:06:21.920 So all those cables from all the different computers in 128 00:06:21.920 --> 00:06:26.399 the Mhtech office snake through the drop ceilings, down the walls, 129 00:06:26.600 --> 00:06:28.480 and eventually plug into a central. 130 00:06:28.160 --> 00:06:31.360 Box, usually hidden away in some dusty equipment closet somewhere. 131 00:06:31.480 --> 00:06:34.720 Yeah exactly. But here's the wild part. To me Janelle's 132 00:06:34.720 --> 00:06:38.519 word document. Once it hits that wire, it's not a 133 00:06:38.560 --> 00:06:42.720 document anymore. It's a stream of binary ones and zeros 134 00:06:43.040 --> 00:06:46.879 represented by electrical pulses. If you hooked up a diagnostic 135 00:06:46.920 --> 00:06:50.240 tool like in a silloscope to that copper wire, you 136 00:06:50.240 --> 00:06:51.800 wouldn't see text or formatting. 137 00:06:51.800 --> 00:06:53.720 You wouldn't see the employee handbook right. 138 00:06:53.759 --> 00:06:56.319 You would just see jagged peaks and valleys of voltage. 139 00:06:56.720 --> 00:06:59.199 A surge of electricity is a one and the absence 140 00:06:59.199 --> 00:07:00.480 of a charge zero. 141 00:07:01.000 --> 00:07:04.800 And because it's pure electricity, Layer one is completely blind. 142 00:07:05.720 --> 00:07:08.519 It doesn't know if it's transmitting an urgent financial spreadsheet 143 00:07:08.639 --> 00:07:11.240 or like a video of a cat playing the piano. 144 00:07:11.319 --> 00:07:12.720 It just doesn't care exactly. 145 00:07:12.839 --> 00:07:15.480 It just moves the voltage pulses from one computer to 146 00:07:15.519 --> 00:07:16.319 the central box. 147 00:07:16.519 --> 00:07:19.199 Historically, that central box was a piece of hardware called 148 00:07:19.199 --> 00:07:22.079 a hub, and the hub was, to put it nicely, 149 00:07:22.120 --> 00:07:25.319 a very dumb device, very dumb. It was essentially just 150 00:07:25.439 --> 00:07:26.720 an electrical reputer. 151 00:07:26.959 --> 00:07:31.079 Yeah, a hub has a fundamental flaw by modern networking standards, 152 00:07:31.680 --> 00:07:35.000 When a hub receives an electrical pulse from Janelle's computer, 153 00:07:35.360 --> 00:07:38.439 it has zero intelligence. It doesn't know who the message 154 00:07:38.519 --> 00:07:38.839 is for. 155 00:07:39.040 --> 00:07:39.759 So what does it do. 156 00:07:40.319 --> 00:07:43.360 It simply makes an exact copy of that pulse and 157 00:07:43.480 --> 00:07:45.959 blasts it out of every single port, sending it to 158 00:07:46.079 --> 00:07:48.800 every single computer connected to the office network. 159 00:07:48.879 --> 00:07:52.199 Wait, hang on, if a hub just blasts every single 160 00:07:52.240 --> 00:07:55.720 electrical pulse to everyone on the network simultaneously, wouldn't that 161 00:07:55.800 --> 00:07:57.519 create absolute chaos? 162 00:07:57.560 --> 00:07:58.199 Total chaos? 163 00:07:58.279 --> 00:08:01.199 I mean, how does Dana's computer know which pulse is 164 00:08:01.240 --> 00:08:04.279 her employee handbook? And how do the fifty other computers 165 00:08:04.319 --> 00:08:05.800 in the office know to ignore it? 166 00:08:05.920 --> 00:08:08.120 That pushes us directly up to the next level of 167 00:08:08.120 --> 00:08:11.720 the blueprint. Because the physical layer is essentially screaming the 168 00:08:11.720 --> 00:08:15.319 message to everyone in the room, the network strictly requires 169 00:08:15.360 --> 00:08:17.639 a filter at the hardware level to sort out all 170 00:08:17.680 --> 00:08:19.879 that noise. Okay, And that brings us to layer two, 171 00:08:19.959 --> 00:08:22.720 the data link layer, and a crucial piece of hardware 172 00:08:22.759 --> 00:08:23.480 called the NIC. 173 00:08:23.959 --> 00:08:28.120 The NIC the network interface card. This is the piece 174 00:08:28.120 --> 00:08:31.199 of hardware that actually plugs into the motherboard of your computer, 175 00:08:31.319 --> 00:08:35.000 right yep. And it's where that twisted pair network cable connects. 176 00:08:35.320 --> 00:08:39.159 The NC basically straddles layer one and layer two, and 177 00:08:39.200 --> 00:08:42.600 it's what gives your computer its unique identity on the network. 178 00:08:42.799 --> 00:08:46.759 Inside every single NIC, permanently burned into a read only 179 00:08:46.799 --> 00:08:49.960 memory chip at the factory, is a unique identifier called 180 00:08:50.000 --> 00:08:54.320 the MC address. MC stands for Media Access Control. 181 00:08:54.039 --> 00:08:56.320 And this is where the formating gets interesting. The source 182 00:08:56.399 --> 00:08:59.240 breaks down the anatomy of a MESS address. It's a 183 00:08:59.279 --> 00:09:00.919 forty eight bit value. 184 00:09:00.559 --> 00:09:03.519 Sometimes called an EUI forty eight or a messe forty eight. 185 00:09:03.679 --> 00:09:06.559 Right, and because humans are frankly terrible at reading a 186 00:09:06.559 --> 00:09:09.240 string of forty eight ones and zeros, it is always 187 00:09:09.279 --> 00:09:11.960 written in hexadecimal format That means base sixteen. 188 00:09:12.000 --> 00:09:14.200 Yeah. The math gets a little weird here a little bit. 189 00:09:14.279 --> 00:09:16.679 Instead of just using zero through nine, it uses the 190 00:09:16.720 --> 00:09:19.399 numbers zero through nine plus the letters A through F 191 00:09:19.480 --> 00:09:21.200 to represent values up to fifteen. 192 00:09:21.399 --> 00:09:24.279 What's fascinating here is how the industry ensures this address 193 00:09:24.360 --> 00:09:27.960 is globally unique. No two network interface cards in the 194 00:09:28.120 --> 00:09:32.399 entire world share the same MS address. Never The forty 195 00:09:32.399 --> 00:09:35.399 eight bits are split in half. The first twenty four 196 00:09:35.440 --> 00:09:40.639 bits make up the organizationally unique identifier or OUI. The 197 00:09:40.720 --> 00:09:45.120 Institute of Electrical and Electronics Engineers the IEE assigns this 198 00:09:45.200 --> 00:09:48.080 specific code to the manufacturer. 199 00:09:47.440 --> 00:09:49.320 So it's like a brand stamp exactly. 200 00:09:49.360 --> 00:09:51.919 So Sister gets a specific block of codes, Intel gets 201 00:09:51.919 --> 00:09:54.240 their own block, Apple gets theirs. It's almost like an 202 00:09:54.279 --> 00:09:57.639 area code. Then the last twenty four bits are essentially 203 00:09:57.679 --> 00:10:02.240 the manufacturer's specific serial numb for that exact piece of silicon. 204 00:10:02.399 --> 00:10:05.120 And you can actually see this physical footprint yourself. If 205 00:10:05.120 --> 00:10:06.679 you are listening to this and you're sitting at a 206 00:10:06.679 --> 00:10:09.759 Windows computer, you can open up the command prompt type 207 00:10:09.759 --> 00:10:11.720 in IP canfig all and look for the line that 208 00:10:11.759 --> 00:10:12.879 says physical address. 209 00:10:12.960 --> 00:10:14.039 That is your MC address. 210 00:10:14.120 --> 00:10:15.759 Yeah, if you're on a Mac, you can open a 211 00:10:15.799 --> 00:10:18.080 terminal and type if canfig. You'll see a string of 212 00:10:18.159 --> 00:10:22.039 characters separated by dashes or colons like zero zero four, zero, zero, 213 00:10:22.279 --> 00:10:25.679 zero five six zero, seventy forty nine. That is your 214 00:10:25.679 --> 00:10:28.080 device's permanent, burned in fingerprint. 215 00:10:28.519 --> 00:10:30.960 So, coming back to the chaos of the hub blasting 216 00:10:31.039 --> 00:10:34.200 data everywhere, the NIC is the solution. Think of the 217 00:10:34.279 --> 00:10:36.759 NIC is a highly disciplined bouncer at the door of 218 00:10:36.759 --> 00:10:37.240 your computer. 219 00:10:37.360 --> 00:10:38.559 Oh, I like that a bouncer. 220 00:10:38.879 --> 00:10:42.840 Right when the hub blast Janelle's file out as electrical pulses, 221 00:10:43.600 --> 00:10:47.559 every single NIC on the network receives those pulses. They 222 00:10:47.600 --> 00:10:50.720 all interpret the ones and zeros, but the immediately check 223 00:10:50.759 --> 00:10:54.440 the destination MAAC address stamped on the incoming data and 224 00:10:54.480 --> 00:10:57.399 if it's not for them, if that destination address doesn't 225 00:10:57.399 --> 00:11:01.639 match their own burned in fingerprint, then drops the message entirely. 226 00:11:01.960 --> 00:11:05.399 It acts like it never even happened. Only data's NIC 227 00:11:05.600 --> 00:11:08.919 will see its own MAC address on the incoming data, 228 00:11:08.960 --> 00:11:11.519 accept it, and pass it up to the computer's memory. 229 00:11:11.559 --> 00:11:13.639 Okay, so the bouncer checks the ID to let the 230 00:11:13.679 --> 00:11:16.679 data in. But that means Janelle's massive word document has 231 00:11:16.720 --> 00:11:18.720 to be packaged in a very specific way so the 232 00:11:18.720 --> 00:11:21.600 bouncer can quickly read it right exactly, because a raw, 233 00:11:21.720 --> 00:11:24.759 continuous stream of ones and zeros is pretty much useless 234 00:11:24.759 --> 00:11:26.600 without some kind of structure. 235 00:11:26.159 --> 00:11:28.720 Which introduces the concept of a frame. A frame is 236 00:11:28.720 --> 00:11:32.120 the protocol data unit or PDU for layer two. It 237 00:11:32.200 --> 00:11:34.240 is basically the digital container for the data. 238 00:11:34.320 --> 00:11:37.759 Here's where it gets really interesting. The source suggests visualizing 239 00:11:37.840 --> 00:11:40.360 this frame like one of those pneumatic tube canisters at 240 00:11:40.399 --> 00:11:41.039 a drive in bank. 241 00:11:41.080 --> 00:11:42.279 Oh yeah, the plastic tubes. 242 00:11:42.600 --> 00:11:45.639 Yeah, you put your paper check inside, close the plastic 243 00:11:45.679 --> 00:11:47.960 tube and it gets sucked up the pipe into the building. 244 00:11:48.600 --> 00:11:51.440 The text actually jokes about a little guy named nick 245 00:11:51.639 --> 00:11:54.679 Nick living inside the network card who works at a 246 00:11:54.720 --> 00:11:56.320 table building these canisters. 247 00:11:56.480 --> 00:11:58.120 Little guy doing all the hard. 248 00:11:57.840 --> 00:12:02.120 Work, working overtime. And then which is the frame doesn't 249 00:12:02.159 --> 00:12:04.679 care if it's carrying dirt or diamonds. It doesn't care 250 00:12:04.720 --> 00:12:07.000 if it's the employee handbook or just a quick email. 251 00:12:07.080 --> 00:12:09.320 It just holds the payloads safely. 252 00:12:09.320 --> 00:12:12.960 And that canniser has a very rigid anatomy. In a 253 00:12:13.000 --> 00:12:16.600 generic wired network, the frame starts with a header. You 254 00:12:16.600 --> 00:12:18.120 can think of this as the shipping label. 255 00:12:18.159 --> 00:12:18.399 Okay. 256 00:12:18.679 --> 00:12:21.759 This header contains the destination m may address where it's going, 257 00:12:21.919 --> 00:12:24.200 followed immediately by the source and MAC address. Work came. 258 00:12:25.000 --> 00:12:27.639 Then there's a tight field that tells the receiving system 259 00:12:27.919 --> 00:12:31.080 what kind of data is hidden inside. After the header 260 00:12:31.080 --> 00:12:34.039 comes the payload itself, the actual ones and zeros of 261 00:12:34.039 --> 00:12:37.440 the word document, and finally the cannister ends with a 262 00:12:37.480 --> 00:12:40.320 trailer called the FCS or frame check sequence. 263 00:12:40.639 --> 00:12:43.960 Well, wait a second. If these pneumatic canisters are a 264 00:12:44.039 --> 00:12:47.840 standardized size to move efficiently through the network, how on 265 00:12:47.919 --> 00:12:52.240 earth does a massive fifty page employee handbook with graphics 266 00:12:52.240 --> 00:12:53.639 and formatting fit inside one? 267 00:12:53.799 --> 00:12:56.159 It doesn't. Oh, and this is where the system has 268 00:12:56.200 --> 00:12:59.200 to work over time. A standard frame on a wired 269 00:12:59.200 --> 00:13:01.919 network in general only hold a maximum of fifteen hundred 270 00:13:01.919 --> 00:13:02.639 bytes of data. 271 00:13:02.679 --> 00:13:04.759 Fifteen hundred bytes. That's tiny. 272 00:13:05.000 --> 00:13:08.320 It's an incredibly small amount of information. Yeah, so when 273 00:13:08.399 --> 00:13:11.279 Janelle hits send on a large word document, her computer's 274 00:13:11.279 --> 00:13:14.200 operating system has to step in. The software chops that 275 00:13:14.240 --> 00:13:19.399 massive document into hundreds, maybe thousands, of tiny fifteen hundred 276 00:13:19.399 --> 00:13:22.879 byte chunks. Wow. It hands those sequential chunks to the NIC, 277 00:13:23.440 --> 00:13:26.120 and the NIC stuffs each individual piece into its own 278 00:13:26.120 --> 00:13:29.000 individual frame, its own noumatic canister, and fires them off 279 00:13:29.039 --> 00:13:30.200 down the wire, one by one. 280 00:13:30.279 --> 00:13:31.919 And then Dana's computer has to put it all back 281 00:13:31.960 --> 00:13:32.720 together exactly. 282 00:13:32.840 --> 00:13:35.200 Dana's computer has to catch all those thousands of cannisters, 283 00:13:35.240 --> 00:13:38.519 open them up, extract the payloads, and seamlessly reassemble all 284 00:13:38.519 --> 00:13:39.840 the pieces in the exact right. 285 00:13:39.840 --> 00:13:43.519 Order, which brings up a terrifying thought. We have thousands 286 00:13:43.639 --> 00:13:46.960 or even millions of these little fifteen hundred byte canisters 287 00:13:47.000 --> 00:13:50.480 flying through the copper cables at light speed. What if 288 00:13:50.480 --> 00:13:54.519 an electrical surge from a nearby power cord flips a 289 00:13:54.519 --> 00:13:56.960 single one to a zero while it is inside the cable. 290 00:13:57.519 --> 00:14:01.639 It happens, but a corrupted word document is completely useless. 291 00:14:01.320 --> 00:14:04.039 Right, which is why quality control is so important. That's 292 00:14:04.080 --> 00:14:06.480 exactly what the FCS. The frame check sequence at the 293 00:14:06.559 --> 00:14:09.600 end of the canister is for It verifies the integrity 294 00:14:09.600 --> 00:14:12.480 of the data using a mathematical algorithm called a cyclic 295 00:14:12.519 --> 00:14:13.840 redundancy check or. 296 00:14:13.879 --> 00:14:15.519 CRC CRC okay. 297 00:14:15.720 --> 00:14:19.000 It is fundamentally a form of binary math division wait division. 298 00:14:19.559 --> 00:14:22.639 How does doing long division on a file check for corruption. 299 00:14:22.759 --> 00:14:25.559 That sounds like unnecessary maths, slowing down the transfer. 300 00:14:25.679 --> 00:14:27.879 It sounds crazy, but think of it with simple numbers. 301 00:14:28.320 --> 00:14:31.799 Imagine Janelle's data equals the number ten. Her network card 302 00:14:31.879 --> 00:14:35.120 divides that ten by a specific universally agreed upon key. 303 00:14:35.159 --> 00:14:36.080 Let's say the key is three. 304 00:14:36.120 --> 00:14:38.360 Okay, ten divided by three right, ten. 305 00:14:38.159 --> 00:14:41.159 Divided by three leaves the remainder of one. Janelle's NIC 306 00:14:41.399 --> 00:14:44.440 takes that remainder, the number one, and stamps it into 307 00:14:44.480 --> 00:14:46.919 the XCS trailer at the end of the frame before sending. 308 00:14:46.679 --> 00:14:49.519 It okay, So the remainder travels with the file exactly. 309 00:14:49.840 --> 00:14:53.080 When Dana is receiving NIC gets the canister, it takes 310 00:14:53.080 --> 00:14:56.279 the payload and does the exact same division problem using 311 00:14:56.279 --> 00:15:00.519 the exact same key of three. If Dan also gets 312 00:15:00.519 --> 00:15:03.639 a remainder of one, the math matches perfectly. The file 313 00:15:03.720 --> 00:15:06.080 is safe, the file survived the trip intact, and the 314 00:15:06.080 --> 00:15:10.240 frame is accepted. But if a bit flipped during travel 315 00:15:10.519 --> 00:15:12.039 and that ten became an eleven. 316 00:15:12.440 --> 00:15:13.919 Oh, I see where this is going. 317 00:15:14.200 --> 00:15:17.399 Right, Eleven divided by three leaves the remainder of two. 318 00:15:18.200 --> 00:15:22.120 Dana's computer sees the remainders two, realizes it doesn't match 319 00:15:22.159 --> 00:15:24.879 the one stamped on the trailer and immediately knows that 320 00:15:24.960 --> 00:15:26.399 data was corrupted in transit. 321 00:15:26.759 --> 00:15:28.879 And what does it do with the cryptid canister? Does 322 00:15:28.919 --> 00:15:30.440 it try to fix it somehow? 323 00:15:30.600 --> 00:15:33.919 It drops it instantly? Yeah, the frame is considered garbage 324 00:15:33.919 --> 00:15:36.240 and thrown away, forcing the upper layers of the network 325 00:15:36.240 --> 00:15:39.080 to eventually realize a piece is missing and asks Janelle's 326 00:15:39.080 --> 00:15:41.639 computer to resend that specific fifteen hundred byte chunk. 327 00:15:41.799 --> 00:15:44.639 It just throws it away. That is ruthless, but I 328 00:15:44.639 --> 00:15:47.159 guess it has to be to ensure perfect data integrity. 329 00:15:47.240 --> 00:15:49.320 But hold on, I have another logistical problem here late 330 00:15:49.399 --> 00:15:52.039 on me. For Janelle's computer to build this canister in 331 00:15:52.080 --> 00:15:55.240 the first place, it needs to write Dana's specific destination 332 00:15:55.559 --> 00:15:59.279 NEC address on the header. But how does Janelle's computer 333 00:15:59.519 --> 00:16:03.519 know DANA'SMEC address. It's not like there's a physical phone 334 00:16:03.519 --> 00:16:06.600 book of forty eight bit hexadecimal numbers sitting on Janelle's desk. 335 00:16:06.759 --> 00:16:09.759 That's a great question. It needs that address to function. 336 00:16:10.080 --> 00:16:13.519 So if Janelle's computer doesn't know DANA'SMEC, it uses a 337 00:16:13.639 --> 00:16:17.600 very specific mechanism to find out. It sends an investigative 338 00:16:17.600 --> 00:16:19.440 message called a broadcast. 339 00:16:18.919 --> 00:16:20.240 Frame broadcast frame. 340 00:16:20.320 --> 00:16:22.960 Instead of targeting a specific forty eight bit device address, 341 00:16:23.399 --> 00:16:30.360 it uses the universal MAC address ffffffffffff all F. 342 00:16:30.480 --> 00:16:33.000 Because it's hexadesimal, F is the highest possible value. 343 00:16:33.080 --> 00:16:35.600 You got it. That all F address is the universal 344 00:16:35.639 --> 00:16:38.919 broadcast code. When a network card sees a frame address 345 00:16:38.960 --> 00:16:42.000 to all FS, the bouncer doesn't drop it. Every single 346 00:16:42.000 --> 00:16:44.480 computer on the mhtech ed network is forced to accept 347 00:16:44.480 --> 00:16:47.399 that specific frame, open the canister, and read the payload 348 00:16:47.519 --> 00:16:50.600 like a company wide memo exactly, and the payload basically 349 00:16:50.600 --> 00:16:52.879 acts as a megaphone saying, Hey, whoever has the IP 350 00:16:52.919 --> 00:16:55.399 address for Dana's computer, please reply and tell me your 351 00:16:55.399 --> 00:16:57.039 physical MAC address. 352 00:16:56.919 --> 00:16:59.399 And then Dana's computer answers yep. 353 00:16:59.559 --> 00:17:03.519 Dana's computer sees the request, realizes it's the intended target, 354 00:17:03.759 --> 00:17:06.519 and sends a direct reply back with their burned in 355 00:17:06.680 --> 00:17:10.880 MPAC address. Now Janelle's computer caches it in memory and 356 00:17:10.920 --> 00:17:13.759 can send the thousands of document frames directly. 357 00:17:14.000 --> 00:17:16.160 But if we combine this with what we learned about 358 00:17:16.240 --> 00:17:21.559 hubs earlier, hubbs blindly blast every electrical pulse out of 359 00:17:21.599 --> 00:17:24.680 every port, and now we are adding broadcast frames that 360 00:17:24.799 --> 00:17:28.240 force every single computer to open and read the message. 361 00:17:28.319 --> 00:17:32.440 If Mhtech has fifty or one hundred computers all sending 362 00:17:32.480 --> 00:17:36.319 broadcasts and hubs blasting everything everywhere, that sounds like a 363 00:17:36.359 --> 00:17:39.319 recipe for a complete network meltdown. The cables would be 364 00:17:39.400 --> 00:17:41.119 absolutely saturated with noise. 365 00:17:41.279 --> 00:17:43.480 If we connect this to the bigger picture, you have 366 00:17:43.640 --> 00:17:46.440 just identified why the networking industry had to evolve. 367 00:17:46.480 --> 00:17:47.720 Oh good, so they fixed it. 368 00:17:47.799 --> 00:17:50.599 They had to. Relying on hubbs would completely break a 369 00:17:50.720 --> 00:17:54.160 large modern network. The sheer volume of traffic, the constant 370 00:17:54.200 --> 00:17:57.359 copying of frames would overwhelm the physical bandwidth of the cables. 371 00:17:57.680 --> 00:18:00.960 This is exactly why Layer two hardware advanced. The dumb 372 00:18:01.039 --> 00:18:03.559 hub was replaced by an intelligent device called a switch. 373 00:18:03.880 --> 00:18:06.240 The switch, which, if you look at it in the 374 00:18:06.240 --> 00:18:09.200 equipment closet, looks almost exactly like a hub, doesn't It 375 00:18:09.279 --> 00:18:11.200 Just a metal box with a bunch of ports for 376 00:18:11.240 --> 00:18:12.319 cables to plug into. 377 00:18:12.720 --> 00:18:16.759 Physically similar, but internally, a switch is a massive leap forward, 378 00:18:17.319 --> 00:18:21.400 a switch actually learns. It learns it contains a memory bank. 379 00:18:22.240 --> 00:18:24.799 Every time a device sends a frame into the switch, 380 00:18:25.039 --> 00:18:28.200 the switch looks at the source MK address on a header. 381 00:18:28.680 --> 00:18:31.319 It notes odd, Janelle's MK address is coming in on 382 00:18:31.359 --> 00:18:34.839 port two. It writes that down in a dynamic table. 383 00:18:34.920 --> 00:18:38.599 Oh wow. When Dana replies, it logs Dana's MAA address 384 00:18:38.680 --> 00:18:42.240 is on port five. It dynamically builds a literal map 385 00:18:42.279 --> 00:18:43.759 of the office network. 386 00:18:43.440 --> 00:18:45.240 So it's not guessing anymore exactly. 387 00:18:45.880 --> 00:18:48.200 The next time Janelle sends a frame destined for Dana's 388 00:18:48.240 --> 00:18:51.799 MTA address, the switch consoles its internal table. It knows 389 00:18:51.880 --> 00:18:54.519 Dana's on port five. So instead of blasting the electrical 390 00:18:54.599 --> 00:18:56.759 pulses out of every single port like a hub, it 391 00:18:56.839 --> 00:18:59.960 sends the voltage only down the specific cable plugged into port. 392 00:19:00.519 --> 00:19:01.960 That is so much more efficient. 393 00:19:02.200 --> 00:19:05.240 It revolutionized network efficiency by turning a noisy room where 394 00:19:05.240 --> 00:19:08.200 everyone is shouting over each other into a sophisticated system 395 00:19:08.240 --> 00:19:09.799 of private direct telephone lines. 396 00:19:10.000 --> 00:19:10.839 That's incredible. 397 00:19:10.880 --> 00:19:12.480 And if you are listening to this on Wi Fi 398 00:19:12.519 --> 00:19:15.319 at a busy coffee shop right now, the wireless router 399 00:19:15.480 --> 00:19:19.000 is acting exactly like a modern switch mapping the mac 400 00:19:19.200 --> 00:19:22.480 addresses of all the laptops and phones, filtering the traffic 401 00:19:22.559 --> 00:19:26.039