1 1 00:00:00,570 --> 00:00:03,020 Network infrastructure devices. 2 2 00:00:03,020 --> 00:00:04,840 Now, for the Network+ exam, 3 3 00:00:04,840 --> 00:00:05,673 you have to be able 4 4 00:00:05,673 --> 00:00:08,570 to identify network infrastructure devices. 5 5 00:00:08,570 --> 00:00:10,640 This means, you have to identify their icons, 6 6 00:00:10,640 --> 00:00:12,340 as well as knowing what they do, 7 7 00:00:12,340 --> 00:00:14,470 what broadcast domains they're going to break up, 8 8 00:00:14,470 --> 00:00:16,720 and what collision domains they're going to break up. 9 9 00:00:16,720 --> 00:00:19,330 We're going to talk about all of that in this lesson. 10 10 00:00:19,330 --> 00:00:21,140 Now, the primary devices that we use 11 11 00:00:21,140 --> 00:00:23,720 in our networks today are routers and switches. 12 12 00:00:23,720 --> 00:00:26,790 These devices actually evolve from bridges and hubs. 13 13 00:00:26,790 --> 00:00:29,300 And we're going to talk about this by starting out with hubs 14 14 00:00:29,300 --> 00:00:31,670 and working our way towards more modern things. 15 15 00:00:31,670 --> 00:00:33,160 Now, as we look at hubs, 16 16 00:00:33,160 --> 00:00:34,780 hubs are a layer 1 device, 17 17 00:00:34,780 --> 00:00:36,340 they are a physical device. 18 18 00:00:36,340 --> 00:00:38,460 They're used to connect multiple network devices 19 19 00:00:38,460 --> 00:00:40,080 and workstations together. 20 20 00:00:40,080 --> 00:00:42,520 You can identify them by a square icon 21 21 00:00:42,520 --> 00:00:44,610 with an arrow pointing in both directions 22 22 00:00:44,610 --> 00:00:46,210 when you see them on a chart. 23 23 00:00:46,210 --> 00:00:48,910 These are known as multiport repeaters. 24 24 00:00:48,910 --> 00:00:51,620 Now, there are basically three different types of hubs. 25 25 00:00:51,620 --> 00:00:55,090 We have passive hubs, active hubs, and smart hubs. 26 26 00:00:55,090 --> 00:00:57,610 A passive hub is simply going to repeat the signal, 27 27 00:00:57,610 --> 00:00:59,810 but it's going to give no amplification. 28 28 00:00:59,810 --> 00:01:01,650 Think about this like a splitter, 29 29 00:01:01,650 --> 00:01:04,810 if I have an 8-port hub and something comes in one port, 30 30 00:01:04,810 --> 00:01:06,510 it's going to go ahead and pass it out 31 31 00:01:06,510 --> 00:01:09,490 to all the other ports, ports two through seven. 32 32 00:01:09,490 --> 00:01:10,950 Now, if I have an active hub, 33 33 00:01:10,950 --> 00:01:13,160 it's going to do exactly the same thing. 34 34 00:01:13,160 --> 00:01:14,240 But the difference is 35 35 00:01:14,240 --> 00:01:16,030 it's going to take the signal that got in, 36 36 00:01:16,030 --> 00:01:18,850 and it's going to boost it back up, and then send it out. 37 37 00:01:18,850 --> 00:01:21,330 Now, what I mean here when I talk about boosting the signal 38 38 00:01:21,330 --> 00:01:24,000 is trying to overcome that 100-meter limitation 39 39 00:01:24,000 --> 00:01:26,210 that we have with twisted pair cabling. 40 40 00:01:26,210 --> 00:01:28,740 Because twisted pair can only go 100 meters, 41 41 00:01:28,740 --> 00:01:31,290 if you hit a passive hub, guess what? 42 42 00:01:31,290 --> 00:01:33,240 That's still part of your 100 meters. 43 43 00:01:33,240 --> 00:01:34,770 So, if I have a 100-meter cable, 44 44 00:01:34,770 --> 00:01:37,230 a passive hub, and a 50 meter cable, 45 45 00:01:37,230 --> 00:01:39,870 it treats it like it's 150-meter cable, 46 46 00:01:39,870 --> 00:01:41,680 and your network's not going to work well. 47 47 00:01:41,680 --> 00:01:44,860 So, if you need to go long distances, you need an active hub, 48 48 00:01:44,860 --> 00:01:47,320 because it gets power, takes that signal in, 49 49 00:01:47,320 --> 00:01:51,350 boosts it back up, and restarts that 100-meter count for you. 50 50 00:01:51,350 --> 00:01:53,240 Now, for example, my office building here 51 51 00:01:53,240 --> 00:01:55,010 is 300 meters in length. 52 52 00:01:55,010 --> 00:01:57,460 I can only go 100 meters with Cat 5, right? 53 53 00:01:57,460 --> 00:01:59,400 So, I might go 60 or 70 meters, 54 54 00:01:59,400 --> 00:02:01,180 and then put an active hub in there, 55 55 00:02:01,180 --> 00:02:03,120 then, I can go another 60 or 70 meters, 56 56 00:02:03,120 --> 00:02:04,520 put another active hub in there, 57 57 00:02:04,520 --> 00:02:07,550 then go another 60 or 70 meters, put an active hub in there. 58 58 00:02:07,550 --> 00:02:10,950 And every time I do it, it restarts that 100-meter limit. 59 59 00:02:10,950 --> 00:02:13,330 Now, notice I only went 60 to 70 meters 60 60 00:02:13,330 --> 00:02:14,650 and then put the hub in there. 61 61 00:02:14,650 --> 00:02:15,700 Why is that? 62 62 00:02:15,700 --> 00:02:17,340 Well, it's just the best practice. 63 63 00:02:17,340 --> 00:02:20,120 If you only use 60 to 70% of that cable length, 64 64 00:02:20,120 --> 00:02:20,953 it's going to make sure 65 65 00:02:20,953 --> 00:02:22,870 you're not coming up towards that 100 meters, 66 66 00:02:22,870 --> 00:02:25,360 because sometimes you just don't count things right, 67 67 00:02:25,360 --> 00:02:26,360 and you might go over 68 68 00:02:26,360 --> 00:02:27,950 and then your network's going to have problems. 69 69 00:02:27,950 --> 00:02:31,130 So, I like to keep it much further away than 100 meters. 70 70 00:02:31,130 --> 00:02:33,250 But again, if you're using a passive hub, 71 71 00:02:33,250 --> 00:02:35,720 all of those connections would have been added together 72 72 00:02:35,720 --> 00:02:37,950 and it would have had about 300 meters of cable 73 73 00:02:37,950 --> 00:02:39,540 and it wouldn't work. 74 74 00:02:39,540 --> 00:02:41,350 Now, if I had three 60s in there, 75 75 00:02:41,350 --> 00:02:44,120 that's going to be 180 meters of cable, right? 76 76 00:02:44,120 --> 00:02:46,290 But if I put that active hub in there each time, 77 77 00:02:46,290 --> 00:02:48,457 I have 60 and 60 and 60. 78 78 00:02:48,457 --> 00:02:49,900 And so it's not 180. 79 79 00:02:49,900 --> 00:02:51,940 It's three 60s that way. 80 80 00:02:51,940 --> 00:02:54,370 Now, the third thing we talked about is a smart hub, 81 81 00:02:54,370 --> 00:02:56,240 and a smart hub is an active hub, 82 82 00:02:56,240 --> 00:02:57,470 but it has enhanced features 83 83 00:02:57,470 --> 00:02:59,640 like Simple Network Management Protocol 84 84 00:02:59,640 --> 00:03:01,390 so that I can actively control that hub 85 85 00:03:01,390 --> 00:03:03,160 and configure it from a distance. 86 86 00:03:03,160 --> 00:03:04,530 It's not just a dumb device, 87 87 00:03:04,530 --> 00:03:07,360 but it adds a little bit of intelligence this way. 88 88 00:03:07,360 --> 00:03:09,190 Overall though, in modern networks, 89 89 00:03:09,190 --> 00:03:11,200 you are not going to see hubs. 90 90 00:03:11,200 --> 00:03:13,740 Almost exclusively, we're going to use switches. 91 91 00:03:13,740 --> 00:03:16,400 And I'm going to show you why in just a few minutes. 92 92 00:03:16,400 --> 00:03:17,930 The next thing we need to talk about here though, 93 93 00:03:17,930 --> 00:03:19,420 is collision domains. 94 94 00:03:19,420 --> 00:03:22,270 When I talk about a hub, it is a layer 1 device. 95 95 00:03:22,270 --> 00:03:23,860 And like I said, it's dumb. 96 96 00:03:23,860 --> 00:03:25,920 All it does is repeat what it's told. 97 97 00:03:25,920 --> 00:03:27,330 And because it can be used 98 98 00:03:27,330 --> 00:03:29,090 to connect multiple network segments together, 99 99 00:03:29,090 --> 00:03:30,410 guess what we do? 100 100 00:03:30,410 --> 00:03:32,250 We're actually going to make a bigger collision domain 101 101 00:03:32,250 --> 00:03:33,470 by doing that. 102 102 00:03:33,470 --> 00:03:35,620 Let's say we want to take five or six computers 103 103 00:03:35,620 --> 00:03:37,200 and make them all talk together. 104 104 00:03:37,200 --> 00:03:39,310 Well, we need a hub to do that. 105 105 00:03:39,310 --> 00:03:42,940 Each LAN segment then becomes a separate collision domain. 106 106 00:03:42,940 --> 00:03:45,630 But hubs don't break up collision domains. 107 107 00:03:45,630 --> 00:03:47,330 Instead, they connect them. 108 108 00:03:47,330 --> 00:03:49,470 So, if I use this diagram here, 109 109 00:03:49,470 --> 00:03:52,430 you can see that there are two 4-port hubs. 110 110 00:03:52,430 --> 00:03:54,110 I have three machines on the left side, 111 111 00:03:54,110 --> 00:03:55,470 and they're talking to one hub. 112 112 00:03:55,470 --> 00:03:56,910 I have two machines on the right side, 113 113 00:03:56,910 --> 00:03:58,290 and they're talking to their hub. 114 114 00:03:58,290 --> 00:04:00,490 And the hubs are communicating together. 115 115 00:04:00,490 --> 00:04:02,490 This is as if all of these devices 116 116 00:04:02,490 --> 00:04:04,960 were on one long bus cable, 117 117 00:04:04,960 --> 00:04:07,400 they're all treated as one large collision domain. 118 118 00:04:07,400 --> 00:04:10,610 And that becomes a big issue as we get into bigger networks, 119 119 00:04:10,610 --> 00:04:14,390 and we start putting in a 24-port hub or a 48-port hub, 120 120 00:04:14,390 --> 00:04:17,400 because all these machines start to talk at the same time, 121 121 00:04:17,400 --> 00:04:19,380 and we're going to have a lot of collisions. 122 122 00:04:19,380 --> 00:04:21,470 So, how do I fix that? 123 123 00:04:21,470 --> 00:04:24,690 Well, that introduces the concept of a bridge. 124 124 00:04:24,690 --> 00:04:25,900 A bridge is going to analyze 125 125 00:04:25,900 --> 00:04:28,050 the source MAC address in the frame, 126 126 00:04:28,050 --> 00:04:30,940 and it's going to populate an internal MAC address table. 127 127 00:04:30,940 --> 00:04:34,020 Based on that table, it's going to make forwarding decisions 128 128 00:04:34,020 --> 00:04:36,360 based on the destination MAC in those frames 129 129 00:04:36,360 --> 00:04:38,480 because this is a layer 2 device. 130 130 00:04:38,480 --> 00:04:42,050 In our earlier example, we had six machines on two hubs, 131 131 00:04:42,050 --> 00:04:43,870 I can now put a bridge in between them 132 132 00:04:43,870 --> 00:04:46,300 and break them up into two pieces. 133 133 00:04:46,300 --> 00:04:49,010 This information will allow it to only go across 134 134 00:04:49,010 --> 00:04:52,060 when it needs to based on its MAC address. 135 135 00:04:52,060 --> 00:04:54,160 If instead it just wants to talk to another PC 136 136 00:04:54,160 --> 00:04:55,570 that's on the hub it's sharing, 137 137 00:04:55,570 --> 00:04:57,460 it never even has to go to that bridge. 138 138 00:04:57,460 --> 00:04:58,920 And those three machines on the left 139 139 00:04:58,920 --> 00:05:00,900 will never hear the communication. 140 140 00:05:00,900 --> 00:05:03,680 This adds security and efficiency to our network 141 141 00:05:03,680 --> 00:05:06,770 and it breaks up that collision domain into two parts. 142 142 00:05:06,770 --> 00:05:08,480 If I take a hub and I take a bridge 143 143 00:05:08,480 --> 00:05:11,150 and I marry them together, guess what I get? 144 144 00:05:11,150 --> 00:05:12,890 I get a switch. 145 145 00:05:12,890 --> 00:05:16,050 A switch is a layer 2 device just like a bridge. 146 146 00:05:16,050 --> 00:05:18,560 It's used to connect multiple network segments together, 147 147 00:05:18,560 --> 00:05:19,850 just like a hub. 148 148 00:05:19,850 --> 00:05:22,120 Essentially, I want you to think of a switch 149 149 00:05:22,120 --> 00:05:24,070 as a multiport bridge. 150 150 00:05:24,070 --> 00:05:25,840 It's going to have every single port 151 151 00:05:25,840 --> 00:05:29,370 act as if it was a hub with a bridge on every port. 152 152 00:05:29,370 --> 00:05:31,630 This way, it breaks up the collision domain 153 153 00:05:31,630 --> 00:05:34,860 into a single collision domain for each and every port. 154 154 00:05:34,860 --> 00:05:36,300 It's going to learn the MAC addresses 155 155 00:05:36,300 --> 00:05:37,950 of the things that are touching that port. 156 156 00:05:37,950 --> 00:05:39,610 And it's going to make forwarding decisions 157 157 00:05:39,610 --> 00:05:42,610 based on those MAC addresses, just like a bridge would. 158 158 00:05:42,610 --> 00:05:44,500 It's going to analyze the source MAC address 159 159 00:05:44,500 --> 00:05:46,760 and then it's going to decide where to send the information 160 160 00:05:46,760 --> 00:05:50,010 based on its internal table, just like a bridge would. 161 161 00:05:50,010 --> 00:05:52,330 So, when I have a switch, each port on there 162 162 00:05:52,330 --> 00:05:54,980 is going to represent an individual collision domain. 163 163 00:05:54,980 --> 00:05:57,440 But everything on that switch 164 164 00:05:57,440 --> 00:06:00,000 is all part of the same broadcast domain. 165 165 00:06:00,000 --> 00:06:02,370 And we'll talk more about this as we go through this lesson 166 166 00:06:02,370 --> 00:06:04,020 and we go through this section. 167 167 00:06:04,020 --> 00:06:06,820 Now, let's talk about how this works in the real world 168 168 00:06:06,820 --> 00:06:08,290 when we're dealing with a switch. 169 169 00:06:08,290 --> 00:06:09,490 Now, let's say we have, 170 170 00:06:09,490 --> 00:06:10,820 I'm sitting here at PC1, 171 171 00:06:10,820 --> 00:06:13,010 and I want to take remote control of the server 172 172 00:06:13,010 --> 00:06:15,450 by using SSH or Secure Shell. 173 173 00:06:15,450 --> 00:06:17,160 Well, how can I do that? 174 174 00:06:17,160 --> 00:06:18,880 Well, if I'm sitting here on PC1, 175 175 00:06:18,880 --> 00:06:22,080 and I have a MAC address, let's say of 12 Bs. 176 176 00:06:22,080 --> 00:06:23,420 I want to talk to the server 177 177 00:06:23,420 --> 00:06:26,150 who has a MAC address of all 12 Cs. 178 178 00:06:26,150 --> 00:06:29,170 I'm going to refer to PC1's MAC address as BB, 179 179 00:06:29,170 --> 00:06:32,510 and server's MAC address as CC, for simplicity's sake, 180 180 00:06:32,510 --> 00:06:34,890 as I go through and talk in this lesson. 181 181 00:06:34,890 --> 00:06:37,100 Now, notice I have the switch tables at the bottom 182 182 00:06:37,100 --> 00:06:39,040 and right now, they're empty. 183 183 00:06:39,040 --> 00:06:40,930 They don't even know who's connected to them, 184 184 00:06:40,930 --> 00:06:43,980 but when PC1 talks the first time, 185 185 00:06:43,980 --> 00:06:46,487 its MAC address at BB says to switch one, 186 186 00:06:46,487 --> 00:06:49,000 "Hey, I want to talk to server CC." 187 187 00:06:49,000 --> 00:06:51,450 So, it sends out a thing called an ARP packet. 188 188 00:06:51,450 --> 00:06:53,610 That ARP packet is going to go to switch one 189 189 00:06:53,610 --> 00:06:55,170 and check its table. 190 190 00:06:55,170 --> 00:06:56,367 If the table sees it and says, 191 191 00:06:56,367 --> 00:06:58,847 "Well, I don't know how to get to CC. 192 192 00:06:58,847 --> 00:07:00,717 So, I'm going to push out that ARP packet 193 193 00:07:00,717 --> 00:07:03,467 to every other port that I have on my switch 194 194 00:07:03,467 --> 00:07:05,810 and see if I can find it for you." 195 195 00:07:05,810 --> 00:07:07,060 Now, before the switch starts 196 196 00:07:07,060 --> 00:07:09,760 pushing that information out to try to find CC, 197 197 00:07:09,760 --> 00:07:11,810 it does know one thing for certain. 198 198 00:07:11,810 --> 00:07:14,600 It knows where BB is because it just talked to it. 199 199 00:07:14,600 --> 00:07:17,670 So, since BB came up on port 0/1, 200 200 00:07:17,670 --> 00:07:19,560 it wants to put that in its table, 201 201 00:07:19,560 --> 00:07:20,760 and then it's going to push out 202 202 00:07:20,760 --> 00:07:22,760 the ARP packet to everyone else. 203 203 00:07:22,760 --> 00:07:24,347 So, PC2 then says, 204 204 00:07:24,347 --> 00:07:27,670 "Hey, I'm not CC, so I'm going to ignore you". 205 205 00:07:27,670 --> 00:07:28,503 PC5 goes, 206 206 00:07:28,503 --> 00:07:31,430 "I'm not CC", and it ignores the switch, as well. 207 207 00:07:31,430 --> 00:07:32,897 Switch two goes, 208 208 00:07:32,897 --> 00:07:34,457 "I don't know who CC is, 209 209 00:07:34,457 --> 00:07:36,697 but even though it's not my MAC address table, 210 210 00:07:36,697 --> 00:07:38,707 I'll forward that out to all the other people 211 211 00:07:38,707 --> 00:07:41,590 on my switch and see if I can find it." 212 212 00:07:41,590 --> 00:07:42,423 That's the idea here. 213 213 00:07:42,423 --> 00:07:43,940 That's what we do with a broadcast. 214 214 00:07:43,940 --> 00:07:45,930 So, it sends it out to its broadcast domain, 215 215 00:07:45,930 --> 00:07:49,070 which has PC3, PC4, and server. 216 216 00:07:49,070 --> 00:07:50,630 And the ARP packet goes out 217 217 00:07:50,630 --> 00:07:52,027 and it goes, "Hey, I also learned 218 218 00:07:52,027 --> 00:07:54,357 that switch one knows where BB is. 219 219 00:07:54,357 --> 00:07:56,327 So, I'm going to put that in my port table. 220 220 00:07:56,327 --> 00:07:57,887 So, if people ask me for BB 221 221 00:07:57,887 --> 00:07:59,450 I know who to talk to." 222 222 00:07:59,450 --> 00:08:00,510 And as the ARP goes out, 223 223 00:08:00,510 --> 00:08:03,090 it goes out to all of the servers and all of the PCs, 224 224 00:08:03,090 --> 00:08:05,530 the server goes, "Oh, hey, I'm CC." 225 225 00:08:05,530 --> 00:08:07,830 So, it responds with an ARP packet back to switch two 226 226 00:08:07,830 --> 00:08:09,387 and says, "Hey, CC? 227 227 00:08:09,387 --> 00:08:10,327 That's me. 228 228 00:08:10,327 --> 00:08:12,230 You should send me all that traffic." 229 229 00:08:12,230 --> 00:08:14,040 So, what is switch two going to do? 230 230 00:08:14,040 --> 00:08:17,480 It's going to populate its table with CC being on port two, 231 231 00:08:17,480 --> 00:08:20,480 and it forwards that back to the requester on switch one. 232 232 00:08:20,480 --> 00:08:22,910 When switch one gets it, it populates its table 233 233 00:08:22,910 --> 00:08:25,750 and pushes it back to the requester at PC1. 234 234 00:08:25,750 --> 00:08:27,780 At this point, every one in the network 235 235 00:08:27,780 --> 00:08:30,180 got query to say, "Who is CC?" 236 236 00:08:30,180 --> 00:08:31,420 And that was a lot of traffic 237 237 00:08:31,420 --> 00:08:33,310 to figure out who the server was. 238 238 00:08:33,310 --> 00:08:35,740 That worked pretty much just like a hub, right? 239 239 00:08:35,740 --> 00:08:36,910 But at this point, 240 240 00:08:36,910 --> 00:08:40,490 everybody now knows where CC is and BB is. 241 241 00:08:40,490 --> 00:08:41,900 And so now that we know that, 242 242 00:08:41,900 --> 00:08:44,210 when PC1 sends out the SSH packet 243 243 00:08:44,210 --> 00:08:46,000 and says, "I want to talk." 244 244 00:08:46,000 --> 00:08:47,220 Guess what happens? 245 245 00:08:47,220 --> 00:08:48,750 It goes to switch one 246 246 00:08:48,750 --> 00:08:50,860 and instead of bugging everybody, 247 247 00:08:50,860 --> 00:08:54,000 switch one only sends it out port 0/2 248 248 00:08:54,000 --> 00:08:57,090 because it knows that is where CC was. 249 249 00:08:57,090 --> 00:08:59,640 That gets to switch two and when switch two gets it, 250 250 00:08:59,640 --> 00:09:02,270 it's going to send it out it's port 0/2, 251 251 00:09:02,270 --> 00:09:04,800 because it knows that's where server was. 252 252 00:09:04,800 --> 00:09:07,890 So, now we have a two-way connection that's been established 253 253 00:09:07,890 --> 00:09:11,760 between the PC and the server through those two switches. 254 254 00:09:11,760 --> 00:09:13,490 And all the other PCs out there, 255 255 00:09:13,490 --> 00:09:16,730 PC2, PC3, PC4, and PC5, 256 256 00:09:16,730 --> 00:09:18,140 they don't hear any of this 257 257 00:09:18,140 --> 00:09:19,370 and they operate on their own 258 258 00:09:19,370 --> 00:09:21,470 without dealing with that SSH traffic. 259 259 00:09:21,470 --> 00:09:22,910 So, we have just minimized 260 260 00:09:22,910 --> 00:09:24,810 the amount of bandwidth that's been eaten up 261 261 00:09:24,810 --> 00:09:26,110 by five or six times 262 262 00:09:26,110 --> 00:09:28,770 because we removed all that extraneous information 263 263 00:09:28,770 --> 00:09:32,290 and all the extraneous equipment from this equation. 264 264 00:09:32,290 --> 00:09:34,800 This is why switches improve our network performance 265 265 00:09:34,800 --> 00:09:36,480 and our security so much. 266 266 00:09:36,480 --> 00:09:38,320 And at this point, switch one and two 267 267 00:09:38,320 --> 00:09:39,890 are only sending out the traffic 268 268 00:09:39,890 --> 00:09:43,140 between PC1 and server across one line. 269 269 00:09:43,140 --> 00:09:48,140 So, PC2, PC3, PC4, PC5 never hear it 270 270 00:09:48,280 --> 00:09:51,130 and if PC2 and PC3 want to start talking, 271 271 00:09:51,130 --> 00:09:52,530 they could at the same time 272 272 00:09:52,530 --> 00:09:55,350 because these switches also support full duplex. 273 273 00:09:55,350 --> 00:09:56,870 And so, I can have a communication 274 274 00:09:56,870 --> 00:09:58,830 between the server and PC1 275 275 00:09:58,830 --> 00:10:01,200 and another separate communication 276 276 00:10:01,200 --> 00:10:03,340 between PC2 and PC3. 277 277 00:10:03,340 --> 00:10:05,570 And it's not going to disturb each other. 278 278 00:10:05,570 --> 00:10:07,230 This is where our efficiency comes in 279 279 00:10:07,230 --> 00:10:08,660 when we deal with switching. 280 280 00:10:08,660 --> 00:10:10,810 Now, the next thing we have to deal with is a router. 281 281 00:10:10,810 --> 00:10:12,290 Because when we deal with switches, 282 282 00:10:12,290 --> 00:10:14,210 we're dealing with layer 2 devices, 283 283 00:10:14,210 --> 00:10:16,250 we're dealing with MAC addresses, right? 284 284 00:10:16,250 --> 00:10:18,870 That's not going to help us if we go across to the Internet. 285 285 00:10:18,870 --> 00:10:21,650 And so, if we want to connect two dissimilar networks, 286 286 00:10:21,650 --> 00:10:24,100 like an internal network and an external network, 287 287 00:10:24,100 --> 00:10:26,710 i.e. your LAN and the Internet, 288 288 00:10:26,710 --> 00:10:29,160 then we need to make routing decisions. 289 289 00:10:29,160 --> 00:10:30,900 To make these forwarding decisions, 290 290 00:10:30,900 --> 00:10:32,570 also known as routing decisions, 291 291 00:10:32,570 --> 00:10:35,210 this is going to be based on logical network information, 292 292 00:10:35,210 --> 00:10:37,880 such as IPv4 or IPv6. 293 293 00:10:37,880 --> 00:10:39,730 And switches aren't aware of that. 294 294 00:10:39,730 --> 00:10:42,870 Switches only know about layer 2 and MAC addresses. 295 295 00:10:42,870 --> 00:10:46,300 Routers are all about layer 3 and IP addresses. 296 296 00:10:46,300 --> 00:10:48,230 Routers are much more feature-rich 297 297 00:10:48,230 --> 00:10:51,320 and they support a broader range of interface types, as well. 298 298 00:10:51,320 --> 00:10:53,980 And so, you might have a router that has a serial port on it. 299 299 00:10:53,980 --> 00:10:56,500 It might have a copper RJ45 port on it, 300 300 00:10:56,500 --> 00:10:58,670 it might have an ST fiber connector on it, 301 301 00:10:58,670 --> 00:11:02,390 you might have a GBIC or an SPF or a QSPF on it. 302 302 00:11:02,390 --> 00:11:04,130 These all have multiple connectors 303 303 00:11:04,130 --> 00:11:05,650 where we can use a router 304 304 00:11:05,650 --> 00:11:07,510 to connect different networks 305 305 00:11:07,510 --> 00:11:10,090 and even different types across them. 306 306 00:11:10,090 --> 00:11:12,550 Switches, on the other hand, tend to be all one. 307 307 00:11:12,550 --> 00:11:14,760 They're either all fiber or all copper, 308 308 00:11:14,760 --> 00:11:16,540 depending on which one you buy. 309 309 00:11:16,540 --> 00:11:19,580 Now, routers have one distinct advantage over a switch. 310 310 00:11:19,580 --> 00:11:20,860 And this is that they can actually 311 311 00:11:20,860 --> 00:11:23,220 separate out broadcast domains. 312 312 00:11:23,220 --> 00:11:25,190 Now, going back to our earlier example, 313 313 00:11:25,190 --> 00:11:28,300 I had three PCs on the left and two on the right. 314 314 00:11:28,300 --> 00:11:30,460 They're talking to those two switches. 315 315 00:11:30,460 --> 00:11:32,540 Now, if the router wasn't there, 316 316 00:11:32,540 --> 00:11:35,030 this would be just one big broadcast domain 317 317 00:11:35,030 --> 00:11:36,960 with five collision domains in it. 318 318 00:11:36,960 --> 00:11:38,760 Now, because I put a router in there, 319 319 00:11:38,760 --> 00:11:41,480 I actually have two separate broadcast domains. 320 320 00:11:41,480 --> 00:11:43,280 And that's going to help me reduce the traffic 321 321 00:11:43,280 --> 00:11:45,080 and reduce the noise. 322 322 00:11:45,080 --> 00:11:45,990 Now, this is going to lead 323 323 00:11:45,990 --> 00:11:48,020 to a lot of efficiency in our networks. 324 324 00:11:48,020 --> 00:11:50,020 We're not going to get into how routers work 325 325 00:11:50,020 --> 00:11:51,780 at this particular point in time. 326 326 00:11:51,780 --> 00:11:54,080 We will dig into that later in a separate lesson 327 327 00:11:54,080 --> 00:11:56,500 because there is a lot to cover there. 328 328 00:11:56,500 --> 00:11:58,200 Now, another thing you may come across 329 329 00:11:58,200 --> 00:12:00,780 is what's known as a layer 3 switch. 330 330 00:12:00,780 --> 00:12:02,790 And this tends to confuse a lot of students 331 331 00:12:02,790 --> 00:12:05,210 because when we talk about switches being layer 2, 332 332 00:12:05,210 --> 00:12:06,610 and routers being layer 3, 333 333 00:12:06,610 --> 00:12:08,580 it's a lot cleaner and easier. 334 334 00:12:08,580 --> 00:12:12,020 But over time, they decided to make these things 335 335 00:12:12,020 --> 00:12:13,730 and make these things called layer 3 switches, 336 336 00:12:13,730 --> 00:12:15,570 which really muddy the waters. 337 337 00:12:15,570 --> 00:12:17,660 Now, just like we took hubs and bridges, 338 338 00:12:17,660 --> 00:12:19,700 and we combine them to make a switch, 339 339 00:12:19,700 --> 00:12:21,210 well, somebody got the idea 340 340 00:12:21,210 --> 00:12:23,970 of taking a switch and a router and combining them, 341 341 00:12:23,970 --> 00:12:26,440 and they call that a layer 3 switch. 342 342 00:12:26,440 --> 00:12:28,900 Layer 3 switches are layer 3 devices 343 343 00:12:28,900 --> 00:12:30,960 that are used to connect multiple networks together, 344 344 00:12:30,960 --> 00:12:33,470 and they can perform routing functions. 345 345 00:12:33,470 --> 00:12:36,430 Now, they can do routing decisions, just like a router. 346 346 00:12:36,430 --> 00:12:39,460 And they can connect network segments, just like a switch. 347 347 00:12:39,460 --> 00:12:40,950 Because they act like a router, 348 348 00:12:40,950 --> 00:12:42,590 each of their ports is going to act 349 349 00:12:42,590 --> 00:12:46,500 as its own broadcast domain and its own collision domain. 350 350 00:12:46,500 --> 00:12:48,410 This is a really efficient way of doing things 351 351 00:12:48,410 --> 00:12:49,720 on an internal network 352 352 00:12:49,720 --> 00:12:51,580 because you can use these layer 3 switches 353 353 00:12:51,580 --> 00:12:53,050 and do things quickly. 354 354 00:12:53,050 --> 00:12:55,330 Now, if you have a very large network though, 355 355 00:12:55,330 --> 00:12:56,410 I would not recommend 356 356 00:12:56,410 --> 00:12:58,930 using layer 3 switches as your router 357 357 00:12:58,930 --> 00:13:01,050 because they're not as efficient at routing 358 358 00:13:01,050 --> 00:13:02,990 as a dedicated router would be. 359 359 00:13:02,990 --> 00:13:05,750 If you're in a small office or a home office environment, 360 360 00:13:05,750 --> 00:13:07,710 and you have 20 or 30 machines, 361 361 00:13:07,710 --> 00:13:09,590 you can replace a router and a switch 362 362 00:13:09,590 --> 00:13:11,450 with a single layer 3 switch. 363 363 00:13:11,450 --> 00:13:13,300 And that will work well and save you some money 364 364 00:13:13,300 --> 00:13:15,730 because they are cheaper than having two devices 365 365 00:13:15,730 --> 00:13:17,010 cause you only need one. 366 366 00:13:17,010 --> 00:13:19,550 But if you're going to be in a very large network, 367 367 00:13:19,550 --> 00:13:21,640 I do prefer having a dedicated router 368 368 00:13:21,640 --> 00:13:23,240 because they are much faster 369 369 00:13:23,240 --> 00:13:25,240 for large scale routing operations. 370 370 00:13:25,240 --> 00:13:27,330 Now, the last thing I want to talk about here on the screen 371 371 00:13:27,330 --> 00:13:29,540 is that I have a nice little summary chart for you 372 372 00:13:29,540 --> 00:13:31,530 that's going to show you the five types of devices 373 373 00:13:31,530 --> 00:13:32,930 that we just talked about. 374 374 00:13:32,930 --> 00:13:34,850 We talked about hubs and bridges, 375 375 00:13:34,850 --> 00:13:36,920 switches, multilayer switches, 376 376 00:13:36,920 --> 00:13:39,860 also known as layer 3 switches, and routers. 377 377 00:13:39,860 --> 00:13:40,693 It'll show you 378 378 00:13:40,693 --> 00:13:42,810 all the possible collision domains that they have 379 379 00:13:42,810 --> 00:13:45,360 and the possible broadcast domains that they have. 380 380 00:13:45,360 --> 00:13:48,600 Remember, hubs are just like one shared cable, 381 381 00:13:48,600 --> 00:13:50,760 one collision, one broadcast, 382 382 00:13:50,760 --> 00:13:53,300 whereas a bridge adds a collision domain 383 383 00:13:53,300 --> 00:13:54,930 for each port on that bridge, 384 384 00:13:54,930 --> 00:13:57,190 and it still has one broadcast. 385 385 00:13:57,190 --> 00:13:58,800 A switch is just like a bridge 386 386 00:13:58,800 --> 00:14:02,410 and so it has one per port and one broadcast domain. 387 387 00:14:02,410 --> 00:14:05,530 Routers and multilayer switches operate the same way 388 388 00:14:05,530 --> 00:14:07,870 so you have one port that is a collision domain 389 389 00:14:07,870 --> 00:14:11,050 and one port is also a broadcast domain. 390 390 00:14:11,050 --> 00:14:12,760 Now, you can see the layer of operations 391 391 00:14:12,760 --> 00:14:14,770 here on the right side. 392 392 00:14:14,770 --> 00:14:16,610 Hubs are operating at layer 1, 393 393 00:14:16,610 --> 00:14:18,710 bridges and switches operate layer 2, 394 394 00:14:18,710 --> 00:14:21,480 multilayer switches also known as layer 3 switches 395 395 00:14:21,480 --> 00:14:23,550 and routers operate at layer 3. 396 396 00:14:23,550 --> 00:14:25,280 Now, one last thing I want to talk about 397 397 00:14:25,280 --> 00:14:28,120 with multilayer switches or layer 3 switches, 398 398 00:14:28,120 --> 00:14:29,630 and it's for the exam. 399 399 00:14:29,630 --> 00:14:31,400 For the exam, I want you to remember 400 400 00:14:31,400 --> 00:14:33,330 that anytime they mention a switch, 401 401 00:14:33,330 --> 00:14:35,340 they are talking almost exclusively 402 402 00:14:35,340 --> 00:14:37,490 about a layer 2 switch. 403 403 00:14:37,490 --> 00:14:39,800 Whenever you hear the word switch on the exam, 404 404 00:14:39,800 --> 00:14:41,840 always be thinking layer 2 devices 405 405 00:14:41,840 --> 00:14:43,990 that are focused on MAC addresses. 406 406 00:14:43,990 --> 00:14:46,610 If you hear routers, those are layer 3 devices 407 407 00:14:46,610 --> 00:14:48,840 and they're focused on IP addresses. 408 408 00:14:48,840 --> 00:14:50,800 Now, the only exception to this rule 409 409 00:14:50,800 --> 00:14:53,670 is if the test specifically states in the question 410 410 00:14:53,670 --> 00:14:57,860 the phrase multilayer switch or layer 3 switch. 411 411 00:14:57,860 --> 00:15:00,190 If they use those terms of multilayer switch 412 412 00:15:00,190 --> 00:15:01,610 or a layer 3 switch, 413 413 00:15:01,610 --> 00:15:03,770 then, you can treat it like a router. 414 414 00:15:03,770 --> 00:15:05,840 Otherwise, always treat a switch 415 415 00:15:05,840 --> 00:15:08,590 as a layer 2 device for the exam. 416 416 00:15:08,590 --> 00:15:10,330 This trips up a lot of my students 417 417 00:15:10,330 --> 00:15:11,170 who are used to dealing 418 418 00:15:11,170 --> 00:15:13,110 with switches and routers in the real world 419 419 00:15:13,110 --> 00:15:15,450 because most switches you're going to buy nowadays 420 420 00:15:15,450 --> 00:15:17,670 in a small office home office environment 421 421 00:15:17,670 --> 00:15:20,250 are going to be layer 3 or multilayer switches. 422 422 00:15:20,250 --> 00:15:23,313 But for the exam, a switch is a layer 2 device.