1 00:00:00,570 --> 00:00:03,030 Network infrastructure devices. 2 00:00:03,030 --> 00:00:05,640 Now, for the Network plus exam, you have to be able 3 00:00:05,640 --> 00:00:08,580 to identify network infrastructure devices. 4 00:00:08,580 --> 00:00:10,650 This means you have to identify their icons 5 00:00:10,650 --> 00:00:12,330 as well as knowing what they do, 6 00:00:12,330 --> 00:00:14,520 what broadcast domains are going to break up 7 00:00:14,520 --> 00:00:16,740 and what collision domains they're going to break up. 8 00:00:16,740 --> 00:00:19,350 We're going to talk about all of that in this lesson. 9 00:00:19,350 --> 00:00:22,050 Now, the primary devices that we use in our networks today 10 00:00:22,050 --> 00:00:23,730 are routers and switches. 11 00:00:23,730 --> 00:00:26,820 These devices actually evolve from bridges and hubs. 12 00:00:26,820 --> 00:00:29,310 And we're going to talk about this by starting out with hubs 13 00:00:29,310 --> 00:00:31,680 and working our way towards more modern things. 14 00:00:31,680 --> 00:00:34,800 Now as we look at hubs, hubs are a layer one device. 15 00:00:34,800 --> 00:00:36,360 They are a physical device. 16 00:00:36,360 --> 00:00:38,460 They're used to connect multiple network devices 17 00:00:38,460 --> 00:00:40,080 and workstations together. 18 00:00:40,080 --> 00:00:42,540 You can identify them by a square icon 19 00:00:42,540 --> 00:00:44,610 with an arrow pointing in both directions 20 00:00:44,610 --> 00:00:46,230 when you see 'em on a chart. 21 00:00:46,230 --> 00:00:48,930 These are known as multi-port repeaters. 22 00:00:48,930 --> 00:00:51,630 Now, there are basically three different types of hubs. 23 00:00:51,630 --> 00:00:55,110 We have passive hubs, active hubs and smart hubs. 24 00:00:55,110 --> 00:00:57,630 A passive hub is simply going to repeat the signal, 25 00:00:57,630 --> 00:00:59,820 but it's going to give no amplification. 26 00:00:59,820 --> 00:01:01,680 Think about this, like a splitter. 27 00:01:01,680 --> 00:01:03,030 If I have an eight port hub 28 00:01:03,030 --> 00:01:05,610 and something comes in one port, it's going to go ahead 29 00:01:05,610 --> 00:01:07,770 and pass it out to all the other ports 30 00:01:07,770 --> 00:01:09,510 ports two through seven. 31 00:01:09,510 --> 00:01:10,980 Now, if I have an active hub, 32 00:01:10,980 --> 00:01:13,170 it's going to do exactly the same thing, 33 00:01:13,170 --> 00:01:16,140 but the difference is, it's going to take the signal it got in 34 00:01:16,140 --> 00:01:18,870 and it's going to boost it back up and then send it out. 35 00:01:18,870 --> 00:01:21,330 Now what I mean here when I talk about boosting the signal, 36 00:01:21,330 --> 00:01:24,030 is trying to overcome that 100 meter limitation 37 00:01:24,030 --> 00:01:26,250 that we have with twisted pair cabling. 38 00:01:26,250 --> 00:01:28,770 Because twisted pair can only go 100 meters 39 00:01:28,770 --> 00:01:31,320 if you hit a passive hub, guess what? 40 00:01:31,320 --> 00:01:33,270 That's still part of your 100 meters. 41 00:01:33,270 --> 00:01:35,820 So if I have a 100 meter cable, a passive hub 42 00:01:35,820 --> 00:01:39,900 and a 50 meter cable, it treats it like it's 150 meter cable 43 00:01:39,900 --> 00:01:41,700 and your network's not going to work well. 44 00:01:41,700 --> 00:01:44,880 So if you need to go long distances, you need an active hub 45 00:01:44,880 --> 00:01:47,310 because it gets power, takes that signal in, 46 00:01:47,310 --> 00:01:51,360 boosts it back up and restarts that 100 meter count for you. 47 00:01:51,360 --> 00:01:53,250 Now, for example, my office building here 48 00:01:53,250 --> 00:01:55,020 is 300 meters in length. 49 00:01:55,020 --> 00:01:57,480 I can only go 100 meters with Cat5 50 00:01:57,480 --> 00:01:59,490 so I might go 60 or 70 meters, 51 00:01:59,490 --> 00:02:01,200 then put an active hub in there. 52 00:02:01,200 --> 00:02:03,150 Then I can go another 60 or 70 meters, 53 00:02:03,150 --> 00:02:04,530 put another active hub in there, 54 00:02:04,530 --> 00:02:07,560 then go another 60 or 70 meters, put an active hub in there. 55 00:02:07,560 --> 00:02:10,979 And every time I do it, it restarts that 100 meter limit. 56 00:02:10,979 --> 00:02:13,320 Now notice I only went 60 to 70 meters 57 00:02:13,320 --> 00:02:14,670 and then put the hub in there. 58 00:02:14,670 --> 00:02:17,370 Why is that? Well, it's just the best practice. 59 00:02:17,370 --> 00:02:20,130 If you only use 60 to 70% of that cable length, 60 00:02:20,130 --> 00:02:21,630 it's going to make sure you're not coming up 61 00:02:21,630 --> 00:02:23,970 towards that 100 meters, because sometimes 62 00:02:23,970 --> 00:02:26,400 you just don't count things right and you might go over 63 00:02:26,400 --> 00:02:27,960 and then your network's going to have problems. 64 00:02:27,960 --> 00:02:31,140 So I like to keep it much further away than 100 meters. 65 00:02:31,140 --> 00:02:33,270 But again, if you're using a passive hub, 66 00:02:33,270 --> 00:02:35,730 all of those connections would've been added together 67 00:02:35,730 --> 00:02:37,950 and it would've had about 300 meters of cable 68 00:02:37,950 --> 00:02:39,570 and it wouldn't work. 69 00:02:39,570 --> 00:02:41,340 Now, if I had three 60s in there, 70 00:02:41,340 --> 00:02:43,680 that's going to be 180 meters of cable, 71 00:02:43,680 --> 00:02:45,870 but if I put that active hub in there each time 72 00:02:45,870 --> 00:02:48,240 I have 60 and 60 and 60. 73 00:02:48,240 --> 00:02:51,540 And so it's not 180, it's three 60s that way. 74 00:02:51,540 --> 00:02:54,000 Now the third thing we talked about is a smart hub. 75 00:02:54,000 --> 00:02:55,830 And a smart hub is an active hub, 76 00:02:55,830 --> 00:02:57,060 but it has enhanced features 77 00:02:57,060 --> 00:02:59,220 like simple network management protocol 78 00:02:59,220 --> 00:03:00,990 so that I can actively control that hub 79 00:03:00,990 --> 00:03:02,760 and configure it from a distance. 80 00:03:02,760 --> 00:03:04,110 It's not just a dumb device, 81 00:03:04,110 --> 00:03:06,960 but it adds a little bit of intelligence this way. 82 00:03:06,960 --> 00:03:08,760 Overall though, in modern networks, 83 00:03:08,760 --> 00:03:10,800 you are not going to see hubs. 84 00:03:10,800 --> 00:03:13,320 Almost exclusively, we're going to use switches 85 00:03:13,320 --> 00:03:16,020 and I'm going to show you why in just a few minutes. 86 00:03:16,020 --> 00:03:17,520 The next thing we need to talk about here though 87 00:03:17,520 --> 00:03:19,020 is collision domains. 88 00:03:19,020 --> 00:03:21,870 When I talk about a hub, it is a layer one device. 89 00:03:21,870 --> 00:03:23,460 And like I said, it's dumb. 90 00:03:23,460 --> 00:03:25,530 All it does is repeat what it's told. 91 00:03:25,530 --> 00:03:27,240 And because it can be used to connect 92 00:03:27,240 --> 00:03:30,030 multiple network segments together, guess what we do? 93 00:03:30,030 --> 00:03:31,860 We're actually going to make a bigger collision domain 94 00:03:31,860 --> 00:03:33,060 by doing that. 95 00:03:33,060 --> 00:03:35,220 Let's say we want to take five or six computers 96 00:03:35,220 --> 00:03:36,780 and make 'em all talk together. 97 00:03:36,780 --> 00:03:38,910 Well, we need a hub to do that. 98 00:03:38,910 --> 00:03:42,600 Each land segment then becomes a separate collision domain. 99 00:03:42,600 --> 00:03:45,210 But, hubs don't break up collision domains 100 00:03:45,210 --> 00:03:46,920 instead, they connect them. 101 00:03:46,920 --> 00:03:49,050 So if I use this diagram here, 102 00:03:49,050 --> 00:03:52,020 you can see that there are two four port hubs. 103 00:03:52,020 --> 00:03:53,700 I have three machines on the left side 104 00:03:53,700 --> 00:03:55,050 and they're talking to one hub. 105 00:03:55,050 --> 00:03:56,520 I have two machines on the right side 106 00:03:56,520 --> 00:03:57,900 and they're talking to their hub 107 00:03:57,900 --> 00:04:00,090 and the hubs are communicating together. 108 00:04:00,090 --> 00:04:02,070 This is as if all of these devices 109 00:04:02,070 --> 00:04:04,560 were on one long bus cable. 110 00:04:04,560 --> 00:04:07,170 They're all treated as one large collision domain. 111 00:04:07,170 --> 00:04:10,200 And that becomes a big issue as we get into bigger networks 112 00:04:10,200 --> 00:04:13,980 and we start putting in a 24 port hub or a 48 port hub 113 00:04:13,980 --> 00:04:17,010 because all these machines start to talk at the same time 114 00:04:17,010 --> 00:04:18,959 and we're going to have a lot of collisions. 115 00:04:18,959 --> 00:04:21,060 So how do I fix that? 116 00:04:21,060 --> 00:04:24,270 Well, that introduces the concept of a bridge. 117 00:04:24,270 --> 00:04:25,500 A bridge is going to analyze 118 00:04:25,500 --> 00:04:27,660 the source Mac address in the frame 119 00:04:27,660 --> 00:04:30,630 and it's going to populate an internal Mac address table. 120 00:04:30,630 --> 00:04:33,600 Based on that table, it's going to make forwarding decisions 121 00:04:33,600 --> 00:04:35,970 based on the destination Mac in those frames, 122 00:04:35,970 --> 00:04:38,070 because this is a layer two device. 123 00:04:38,070 --> 00:04:41,670 In our earlier example, we had six machines on two hubs. 124 00:04:41,670 --> 00:04:43,470 I can now put a bridge in between them 125 00:04:43,470 --> 00:04:45,900 and break them up into two pieces. 126 00:04:45,900 --> 00:04:48,600 This information will allow it to only go across 127 00:04:48,600 --> 00:04:51,660 when it needs to, based on its Mac address. 128 00:04:51,660 --> 00:04:53,010 If instead, it just wants to talk 129 00:04:53,010 --> 00:04:55,200 to another PC that's on the hub it's sharing, 130 00:04:55,200 --> 00:04:57,090 it never even has to go to that bridge 131 00:04:57,090 --> 00:04:58,500 and those three machines on the left 132 00:04:58,500 --> 00:05:00,510 will never hear the communication. 133 00:05:00,510 --> 00:05:03,330 This adds security and efficiency to our network 134 00:05:03,330 --> 00:05:06,390 and it breaks up that collision domain into two parts. 135 00:05:06,390 --> 00:05:08,070 If I take a hub and I take a bridge 136 00:05:08,070 --> 00:05:10,740 and I marry them together, guess what I get? 137 00:05:10,740 --> 00:05:12,480 I get a switch. 138 00:05:12,480 --> 00:05:15,660 A switch is a layer two device, just like a bridge. 139 00:05:15,660 --> 00:05:18,180 It's used to connect multiple network segments together, 140 00:05:18,180 --> 00:05:19,440 just like a hub. 141 00:05:19,440 --> 00:05:21,690 Essentially, I want you to think of a switch 142 00:05:21,690 --> 00:05:23,670 as a multi-port bridge. 143 00:05:23,670 --> 00:05:25,440 It's going to have every single port 144 00:05:25,440 --> 00:05:28,980 act as if it was a hub, with a bridge on every port. 145 00:05:28,980 --> 00:05:31,200 This way it breaks up the collision domain 146 00:05:31,200 --> 00:05:34,470 into a single collision domain for each and every port. 147 00:05:34,470 --> 00:05:35,880 It's going to learn the Mac addresses 148 00:05:35,880 --> 00:05:37,650 of the things that are touching that port 149 00:05:37,650 --> 00:05:39,300 and it's going to make forwarding decisions 150 00:05:39,300 --> 00:05:42,210 based on those Mac addresses, just like a bridge would. 151 00:05:42,210 --> 00:05:44,070 It's going to analyze the source Mac address 152 00:05:44,070 --> 00:05:46,380 and that's going to decide where to send the information 153 00:05:46,380 --> 00:05:49,590 based on its internal table, just like a bridge would. 154 00:05:49,590 --> 00:05:51,930 So when I have a switch, each port on there 155 00:05:51,930 --> 00:05:54,600 is going to represent an individual collision domain, 156 00:05:54,600 --> 00:05:57,030 but everything on that switch 157 00:05:57,030 --> 00:05:59,610 is all part of the same broadcast domain. 158 00:05:59,610 --> 00:06:02,400 Now, let's talk about how this works in the real world 159 00:06:02,400 --> 00:06:03,870 when we're dealing with a switch. 160 00:06:03,870 --> 00:06:06,390 Now, let's say I'm sitting here at PC1 161 00:06:06,390 --> 00:06:08,580 and I want to take remote control of the server 162 00:06:08,580 --> 00:06:13,020 by using SSH or Secure Shell, how can I do that? 163 00:06:13,020 --> 00:06:14,490 If I'm sitting here on PC1 164 00:06:14,490 --> 00:06:18,270 and I have a Mac address, let's say, of 12 Bs, I want to talk 165 00:06:18,270 --> 00:06:21,720 to the server who has a Mac address of all 12 Cs. 166 00:06:21,720 --> 00:06:24,780 I'm going to refer to PC1s Mac address as BB 167 00:06:24,780 --> 00:06:28,080 and server's Mac address as CC for simplicity's sake 168 00:06:28,080 --> 00:06:30,450 as I go through and talk in this lesson. 169 00:06:30,450 --> 00:06:32,670 Now notice I have the switch tables at the bottom 170 00:06:32,670 --> 00:06:34,620 and right now they are empty. 171 00:06:34,620 --> 00:06:36,540 They don't even know who's connected to them. 172 00:06:36,540 --> 00:06:40,890 But when PC1 talks the first time, its Mac address of BB 173 00:06:40,890 --> 00:06:44,580 says to switch one, hey, I want to talk to server CC. 174 00:06:44,580 --> 00:06:47,010 So it sends out a thing called an ARP packet. 175 00:06:47,010 --> 00:06:49,200 That ARP packet is going to go to switch one 176 00:06:49,200 --> 00:06:50,730 and check its table. 177 00:06:50,730 --> 00:06:52,020 If the table sees it and says, 178 00:06:52,020 --> 00:06:54,510 well, I don't know how to get to CC, 179 00:06:54,510 --> 00:06:57,570 so I'm going to push out that ARP packet to every other port 180 00:06:57,570 --> 00:07:01,380 that I have on my switch and see if I can find it for you. 181 00:07:01,380 --> 00:07:03,780 Now, before the switch starts pushing that information out 182 00:07:03,780 --> 00:07:07,380 to try to find CC, it does know one thing for certain, 183 00:07:07,380 --> 00:07:10,170 it knows where BB is, because it just talked to it. 184 00:07:10,170 --> 00:07:13,260 So since BB came up on port 0/1, 185 00:07:13,260 --> 00:07:15,150 it wants to put that in its table. 186 00:07:15,150 --> 00:07:16,350 And then it's going to push out 187 00:07:16,350 --> 00:07:18,360 the ARP packet to everyone else. 188 00:07:18,360 --> 00:07:21,870 So PC2 then says, hey, I'm not CC, 189 00:07:21,870 --> 00:07:23,250 so I'm going to ignore you. 190 00:07:23,250 --> 00:07:27,000 PC5 goes, I'm not CC and it ignores the switch as well. 191 00:07:27,000 --> 00:07:30,180 Switch two goes, hmm, I don't know who CC is, 192 00:07:30,180 --> 00:07:32,370 but even though it's not in my Mac address table, 193 00:07:32,370 --> 00:07:35,580 I'll forward that out to all the other people on my switch 194 00:07:35,580 --> 00:07:37,170 and see if I can find it. 195 00:07:37,170 --> 00:07:39,510 That's the idea here. That's what we do with a broadcast. 196 00:07:39,510 --> 00:07:41,520 So it sends it out to its broadcast domain, 197 00:07:41,520 --> 00:07:44,670 which has PC3, PC4 and server 198 00:07:44,670 --> 00:07:46,200 and the ARP packet goes out. 199 00:07:46,200 --> 00:07:47,700 And it goes, hey, I also learned 200 00:07:47,700 --> 00:07:50,040 that switch one knows where BB is, 201 00:07:50,040 --> 00:07:51,990 so I'm going to put that in my port table 202 00:07:51,990 --> 00:07:55,020 So if people ask me for BB, I know who to talk to. 203 00:07:55,020 --> 00:07:56,100 And as the ARP goes out, 204 00:07:56,100 --> 00:07:58,680 it goes out to all of the servers and all of the PCs. 205 00:07:58,680 --> 00:08:01,110 The server goes, oh, hey, I'm CC 206 00:08:01,110 --> 00:08:03,450 so it responds with an ARP packet back to switch two 207 00:08:03,450 --> 00:08:06,000 and says, hey, CC, that's me 208 00:08:06,000 --> 00:08:07,800 you should send me all that traffic. 209 00:08:07,800 --> 00:08:09,630 So what is switch two going to do? 210 00:08:09,630 --> 00:08:13,050 It's going to populate its table with CC being on port two 211 00:08:13,050 --> 00:08:16,080 and it forwards that back to the requester on switch one. 212 00:08:16,080 --> 00:08:18,480 When switch one gets it, it populates its table 213 00:08:18,480 --> 00:08:21,330 and pushes it back to requester at PC1. 214 00:08:21,330 --> 00:08:23,370 At this point, everyone in the network 215 00:08:23,370 --> 00:08:25,770 got queried to say, who is CC? 216 00:08:25,770 --> 00:08:27,000 And that was a lot of traffic 217 00:08:27,000 --> 00:08:28,890 to figure out who the server was. 218 00:08:28,890 --> 00:08:31,350 That worked pretty much just like a hub, 219 00:08:31,350 --> 00:08:33,480 but at this point, everybody now knows 220 00:08:33,480 --> 00:08:36,090 where CC is and BB is. 221 00:08:36,090 --> 00:08:37,440 And so now that we know that 222 00:08:37,440 --> 00:08:40,380 when PC1 sends out the SSH packet and says, 223 00:08:40,380 --> 00:08:42,809 I want to talk, guess what happens? 224 00:08:42,809 --> 00:08:44,340 It goes to switch one. 225 00:08:44,340 --> 00:08:46,470 And instead of bugging everybody, 226 00:08:46,470 --> 00:08:49,560 switch one only sends it out port 0/2 227 00:08:49,560 --> 00:08:52,680 because it knows that is where CC was. 228 00:08:52,680 --> 00:08:55,230 That gets to switch two and when switch two gets it, 229 00:08:55,230 --> 00:08:57,810 it's going to send it out its port 0/2 230 00:08:57,810 --> 00:09:00,360 because it knows that's where server was. 231 00:09:00,360 --> 00:09:03,450 So now we have a two-way connection that's been established 232 00:09:03,450 --> 00:09:07,350 between the PC and the server through those two switches. 233 00:09:07,350 --> 00:09:10,751 And all of the other PCs out there, PC2, PC3, 234 00:09:10,751 --> 00:09:13,740 PC4, and PC5, they don't hear any of this 235 00:09:13,740 --> 00:09:14,940 and they operate on their own 236 00:09:14,940 --> 00:09:17,070 without dealing with that SSH traffic. 237 00:09:17,070 --> 00:09:19,350 So we have just minimized the amount of bandwidth 238 00:09:19,350 --> 00:09:21,690 that's been eaten up by five or six times 239 00:09:21,690 --> 00:09:24,510 because we removed all that extraneous information, 240 00:09:24,510 --> 00:09:27,630 all the extraneous equipment from this equation. 241 00:09:27,630 --> 00:09:30,150 This is why switches improve our network performance 242 00:09:30,150 --> 00:09:31,920 and our security so much. 243 00:09:31,920 --> 00:09:34,560 And at this point, switch one and two are only sending out 244 00:09:34,560 --> 00:09:38,490 the traffic between PC1 and server across one line. 245 00:09:38,490 --> 00:09:43,490 So PC2, PC3, PC4, PC5, never hear it. 246 00:09:43,650 --> 00:09:46,440 And if PC2 and PC3 wanted to start talking, 247 00:09:46,440 --> 00:09:47,850 they could at the same time 248 00:09:47,850 --> 00:09:50,700 because these switches also support full duplex. 249 00:09:50,700 --> 00:09:52,200 And so I can have a communication 250 00:09:52,200 --> 00:09:54,150 between the server and PC1 251 00:09:54,150 --> 00:09:58,680 and another separate communication between PC2 and PC3 252 00:09:58,680 --> 00:10:00,870 and it's not going to disturb each other. 253 00:10:00,870 --> 00:10:02,520 This is where our efficiency comes in 254 00:10:02,520 --> 00:10:03,990 when we deal with switching. 255 00:10:03,990 --> 00:10:06,120 Now, the next thing we have to deal with is a router, 256 00:10:06,120 --> 00:10:07,590 because when we deal with switches, 257 00:10:07,590 --> 00:10:09,510 we're dealing with layer two devices 258 00:10:09,510 --> 00:10:11,580 we're dealing with Mac addresses. 259 00:10:11,580 --> 00:10:14,250 That's not going to help us if we go across to the internet. 260 00:10:14,250 --> 00:10:16,950 And so if we want to connect to dissimilar networks 261 00:10:16,950 --> 00:10:19,590 like an internal network and an external network, 262 00:10:19,590 --> 00:10:22,020 IE, your LAN and the internet, 263 00:10:22,020 --> 00:10:24,480 then we need to make routing decisions. 264 00:10:24,480 --> 00:10:26,220 To make these forwarding decisions 265 00:10:26,220 --> 00:10:27,900 also known as routing decisions 266 00:10:27,900 --> 00:10:30,510 this is going to be based on logical network information 267 00:10:30,510 --> 00:10:35,070 such as IPv4 or IPv6 and switches aren't aware of that. 268 00:10:35,070 --> 00:10:38,190 Switches only know about layer two and Mac addresses. 269 00:10:38,190 --> 00:10:41,610 Routers are all about layer three and IP addresses. 270 00:10:41,610 --> 00:10:43,530 Routers are much more feature rich 271 00:10:43,530 --> 00:10:46,770 and they support a broader range of interface types as well. 272 00:10:46,770 --> 00:10:49,260 And so you might have a router that has a serial port on it. 273 00:10:49,260 --> 00:10:51,810 It might have a copper RJ45 port on it. 274 00:10:51,810 --> 00:10:54,000 It might have an ST fiber connector on it. 275 00:10:54,000 --> 00:10:57,720 You might have a GBIC or an SPF or a QSPF on it. 276 00:10:57,720 --> 00:11:00,960 These all have multiple connectors where we can use a router 277 00:11:00,960 --> 00:11:02,850 to connect different networks 278 00:11:02,850 --> 00:11:05,430 and even different types across them. 279 00:11:05,430 --> 00:11:07,860 Switches on the other hand tend to be all one. 280 00:11:07,860 --> 00:11:10,080 They're either all fiber or all copper, 281 00:11:10,080 --> 00:11:11,850 depending on which one you buy. 282 00:11:11,850 --> 00:11:15,030 Now, routers have one distinct advantage over a switch 283 00:11:15,030 --> 00:11:16,920 and this is that they can actually separate out 284 00:11:16,920 --> 00:11:18,540 broadcast domains. 285 00:11:18,540 --> 00:11:20,490 Now going back to our earlier example, 286 00:11:20,490 --> 00:11:23,610 I had three PCs on the left and two on the right, 287 00:11:23,610 --> 00:11:25,800 they're talking to those two switches. 288 00:11:25,800 --> 00:11:27,840 Now, if the router wasn't there, 289 00:11:27,840 --> 00:11:30,330 this would be just one big broadcast domain 290 00:11:30,330 --> 00:11:32,280 with five collision domains in it. 291 00:11:32,280 --> 00:11:34,050 Now, because I put a router in there, 292 00:11:34,050 --> 00:11:36,840 I actually have two separate broadcast domains 293 00:11:36,840 --> 00:11:37,950 and that's going to help me reduce 294 00:11:37,950 --> 00:11:40,380 the traffic and reduce the noise. 295 00:11:40,380 --> 00:11:41,310 Now, this is going to lead 296 00:11:41,310 --> 00:11:43,350 to a lot of efficiency in our networks. 297 00:11:43,350 --> 00:11:45,330 We're not going to get into how routers work 298 00:11:45,330 --> 00:11:47,100 at this particular point in time 299 00:11:47,100 --> 00:11:49,410 we will dig into that later in a separate lesson 300 00:11:49,410 --> 00:11:51,810 because there is a lot to cover there. 301 00:11:51,810 --> 00:11:53,490 Now, another thing you may come across 302 00:11:53,490 --> 00:11:56,130 is what's known as a layer three switch. 303 00:11:56,130 --> 00:11:58,110 And this tends to confuse a lot of students 304 00:11:58,110 --> 00:12:00,540 because when we talk about switches being layer two 305 00:12:00,540 --> 00:12:01,950 and routers being layer three, 306 00:12:01,950 --> 00:12:03,930 it's a lot cleaner and easier. 307 00:12:03,930 --> 00:12:07,350 But over time, they decide to make these things 308 00:12:07,350 --> 00:12:09,030 and make these things called layer three switches, 309 00:12:09,030 --> 00:12:10,890 which really muddy the waters. 310 00:12:10,890 --> 00:12:12,960 Now, just like we took hubs and bridges 311 00:12:12,960 --> 00:12:15,030 and we combined them to make a switch, 312 00:12:15,030 --> 00:12:16,500 well, somebody got the idea 313 00:12:16,500 --> 00:12:19,320 of taking a switch and a router and combining them 314 00:12:19,320 --> 00:12:21,780 and they call that a layer three switch. 315 00:12:21,780 --> 00:12:24,210 Layer three switches are layer three devices 316 00:12:24,210 --> 00:12:26,310 that are used to connect multiple networks together 317 00:12:26,310 --> 00:12:28,800 and they can perform routing functions. 318 00:12:28,800 --> 00:12:31,770 Now, they can do routing decisions just like a router 319 00:12:31,770 --> 00:12:34,770 and they can connect network segments just like a switch. 320 00:12:34,770 --> 00:12:36,270 Because they act like a router, 321 00:12:36,270 --> 00:12:37,920 each of their ports is going to act 322 00:12:37,920 --> 00:12:41,820 as its own broadcast domain and its own collision domain. 323 00:12:41,820 --> 00:12:43,050 This is a really efficient way 324 00:12:43,050 --> 00:12:45,030 of doing things on an internal network 325 00:12:45,030 --> 00:12:46,890 because you can use these layer three switches 326 00:12:46,890 --> 00:12:48,360 and do things quickly. 327 00:12:48,360 --> 00:12:50,640 Now, if you have a very large network, though, 328 00:12:50,640 --> 00:12:51,690 I would not recommend 329 00:12:51,690 --> 00:12:54,240 using layer three switches as your router 330 00:12:54,240 --> 00:12:56,370 because they're not as efficient at routing 331 00:12:56,370 --> 00:12:58,320 as a dedicated router would be. 332 00:12:58,320 --> 00:13:01,110 If you're in a small office or a home office environment 333 00:13:01,110 --> 00:13:04,137 and you have 20 or 30 machines, you can replace a router 334 00:13:04,137 --> 00:13:06,780 and a switch with a single layer three switch, 335 00:13:06,780 --> 00:13:08,610 and that will work well and save you some money 336 00:13:08,610 --> 00:13:11,040 because they are cheaper than having two devices 337 00:13:11,040 --> 00:13:12,330 'cause you only need one. 338 00:13:12,330 --> 00:13:14,880 But if you're going to be in a very large network, 339 00:13:14,880 --> 00:13:16,980 I do prefer having a dedicated router 340 00:13:16,980 --> 00:13:18,570 because they are much faster 341 00:13:18,570 --> 00:13:20,550 for large scale routing operations. 342 00:13:20,550 --> 00:13:22,680 Now the last thing I want to talk about here on the screen 343 00:13:22,680 --> 00:13:24,870 is I have a nice little summary chart for you 344 00:13:24,870 --> 00:13:26,820 that's going to show you the five type of devices 345 00:13:26,820 --> 00:13:28,260 that we just talked about. 346 00:13:28,260 --> 00:13:30,240 We talked about hubs and bridges, 347 00:13:30,240 --> 00:13:32,250 switches, multi-layer switches, 348 00:13:32,250 --> 00:13:35,190 also known as layer three switches and routers. 349 00:13:35,190 --> 00:13:36,600 It'll show you all the possible 350 00:13:36,600 --> 00:13:38,130 collision domains that they have 351 00:13:38,130 --> 00:13:40,680 and the possible broadcast domains that they have. 352 00:13:40,680 --> 00:13:43,920 Remember, hubs are just like one shared cable, 353 00:13:43,920 --> 00:13:46,080 one collision, one broadcast, 354 00:13:46,080 --> 00:13:48,630 whereas a bridge adds a collision domain 355 00:13:48,630 --> 00:13:50,250 for each port on that bridge, 356 00:13:50,250 --> 00:13:52,500 and it still has one broadcast. 357 00:13:52,500 --> 00:13:54,090 A switch is just like a bridge 358 00:13:54,090 --> 00:13:57,750 and so it has one purport and one broadcast domain. 359 00:13:57,750 --> 00:14:00,840 Routers and multi-layer switches operate the same way 360 00:14:00,840 --> 00:14:03,330 so you have one port that is a collision domain 361 00:14:03,330 --> 00:14:06,360 and one port is also a broadcast domain. 362 00:14:06,360 --> 00:14:08,070 Now you can see the layer of operations 363 00:14:08,070 --> 00:14:10,080 here on the right side. 364 00:14:10,080 --> 00:14:11,940 Hubs are operating at layer one, 365 00:14:11,940 --> 00:14:14,010 bridges and switches operate at layer two 366 00:14:14,010 --> 00:14:16,800 multi-layer switches, also known as layer three switches 367 00:14:16,800 --> 00:14:18,870 and routers operate at layer three. 368 00:14:18,870 --> 00:14:20,610 Now, one last thing I want to talk about 369 00:14:20,610 --> 00:14:23,430 with multi-layer switches or layer three switches 370 00:14:23,430 --> 00:14:24,990 and it's for the exam. 371 00:14:24,990 --> 00:14:26,700 For the exam, I want you to remember 372 00:14:26,700 --> 00:14:28,650 that anytime they mention a switch, 373 00:14:28,650 --> 00:14:30,630 they are talking almost exclusively 374 00:14:30,630 --> 00:14:32,790 about a layer two switch. 375 00:14:32,790 --> 00:14:35,100 Whenever you hear the word switch on the exam, 376 00:14:35,100 --> 00:14:37,140 always be thinking layer two devices 377 00:14:37,140 --> 00:14:39,300 that are focused on Mac addresses. 378 00:14:39,300 --> 00:14:41,910 If you hear routers, those are layer three devices 379 00:14:41,910 --> 00:14:44,160 and they're focused on IP addresses. 380 00:14:44,160 --> 00:14:46,110 Now, the only exception to this rule 381 00:14:46,110 --> 00:14:48,990 is if the test specifically states in the question 382 00:14:48,990 --> 00:14:53,190 the phrase multi-layer switch or layer three switch. 383 00:14:53,190 --> 00:14:55,530 If they use those terms of multi-layer switch 384 00:14:55,530 --> 00:14:59,070 or layer three switch, then you can treat it like a router. 385 00:14:59,070 --> 00:15:01,170 Otherwise, always treat a switch 386 00:15:01,170 --> 00:15:03,900 as a layer two device for the exam. 387 00:15:03,900 --> 00:15:06,480 This trips up a lot of my students who are used to dealing 388 00:15:06,480 --> 00:15:08,430 with switches in routers in the real world, 389 00:15:08,430 --> 00:15:10,800 because most switches you're going to buy nowadays 390 00:15:10,800 --> 00:15:13,020 in a small office, home office environment 391 00:15:13,020 --> 00:15:15,570 are going to be layer three or multilayer switches. 392 00:15:15,570 --> 00:15:18,573 But for the exam, a switch is a layer two device.