1 1 00:00:00,420 --> 00:00:01,450 In the last lesson, 2 2 00:00:01,450 --> 00:00:04,140 we covered a lot of details about subnets. 3 3 00:00:04,140 --> 00:00:05,580 Now, what I want to do in this lesson 4 4 00:00:05,580 --> 00:00:07,590 is take some of these problems and go through them, 5 5 00:00:07,590 --> 00:00:09,770 because you may experience them come test day, 6 6 00:00:09,770 --> 00:00:11,760 sort of walk through how to tackle them. 7 7 00:00:11,760 --> 00:00:13,390 Now, before we get to the first problem, 8 8 00:00:13,390 --> 00:00:15,340 the first thing I want to do is put my chart back 9 9 00:00:15,340 --> 00:00:16,380 on the screen. 10 10 00:00:16,380 --> 00:00:17,980 Now, why am I doing this? 11 11 00:00:17,980 --> 00:00:19,290 Well, because I already told you, 12 12 00:00:19,290 --> 00:00:21,250 you should commit this chart to memory. 13 13 00:00:21,250 --> 00:00:23,340 And when you get down and you sit for the exam, 14 14 00:00:23,340 --> 00:00:24,320 the first thing they're going to do 15 15 00:00:24,320 --> 00:00:26,480 is give you a piece of paper and a pencil. 16 16 00:00:26,480 --> 00:00:27,560 And once they start the clock, 17 17 00:00:27,560 --> 00:00:29,490 you can write whatever you want on that dump sheet. 18 18 00:00:29,490 --> 00:00:31,660 And so, one of the things I put down on my dump sheet 19 19 00:00:31,660 --> 00:00:34,540 or my note sheet, is that I put down from my memory, 20 20 00:00:34,540 --> 00:00:35,980 this chart, and that way, 21 21 00:00:35,980 --> 00:00:38,160 as I get subnetting questions throughout the exam, 22 22 00:00:38,160 --> 00:00:39,760 I can go back and look at those, 23 23 00:00:39,760 --> 00:00:40,860 and so, it makes it really easy. 24 24 00:00:40,860 --> 00:00:42,330 So, I'm going to give it to you here, 25 25 00:00:42,330 --> 00:00:44,910 because I'm assuming you've memorized this before the exam, 26 26 00:00:44,910 --> 00:00:46,370 and you've already written down 27 27 00:00:46,370 --> 00:00:48,130 as you're sitting at your computer. 28 28 00:00:48,130 --> 00:00:49,990 All right, let's take our first question. 29 29 00:00:49,990 --> 00:00:51,640 Let's pretend you're a network administrator 30 30 00:00:51,640 --> 00:00:53,390 for diontraining.com. 31 31 00:00:53,390 --> 00:00:55,810 We decided we're going to open up a small branch office 32 32 00:00:55,810 --> 00:00:56,800 in another city. 33 33 00:00:56,800 --> 00:00:57,940 And so, to support that, 34 34 00:00:57,940 --> 00:01:00,490 I need a subnet for a private IP address 35 35 00:01:00,490 --> 00:01:02,840 that's given to you, for several different networks, 36 36 00:01:02,840 --> 00:01:04,720 based on the different sizes of the departments 37 37 00:01:04,720 --> 00:01:06,330 in this new location. 38 38 00:01:06,330 --> 00:01:07,320 Now, the new office 39 39 00:01:07,320 --> 00:01:11,940 has been given the range of 10.10.10.0/24, 40 40 00:01:11,940 --> 00:01:15,820 which tells you, you have 256 total IP's to work with. 41 41 00:01:15,820 --> 00:01:17,350 Now, when you set up your new network, 42 42 00:01:17,350 --> 00:01:19,450 I want you to configure separate subnets 43 43 00:01:19,450 --> 00:01:21,510 for each of the departments that I'm going to give you. 44 44 00:01:21,510 --> 00:01:23,740 And you're going to tell me which CIDR notation 45 45 00:01:23,740 --> 00:01:26,950 is going to be the summary for each one in each place. 46 46 00:01:26,950 --> 00:01:28,290 Now, I want you to resist the urge 47 47 00:01:28,290 --> 00:01:30,100 of going big for each subnet. 48 48 00:01:30,100 --> 00:01:32,550 I want you to tell me the minimum subnet 49 49 00:01:32,550 --> 00:01:34,690 that would support my requirements. 50 50 00:01:34,690 --> 00:01:36,120 Now, in my new company, 51 51 00:01:36,120 --> 00:01:38,650 we're going to have this number of users that we have. 52 52 00:01:38,650 --> 00:01:41,540 So, first, I have 54 new people in IT, 53 53 00:01:41,540 --> 00:01:44,930 I have 32 new instructors, I have five people in sales, 54 54 00:01:44,930 --> 00:01:46,330 three in administration, 55 55 00:01:46,330 --> 00:01:48,970 and then there's going to be an unused portion that's leftover, 56 56 00:01:48,970 --> 00:01:51,190 and you're going to give me a subnet for that as well. 57 57 00:01:51,190 --> 00:01:52,590 Now, each of these five areas, 58 58 00:01:52,590 --> 00:01:55,370 I need you to tell me what the CIDR notation is for it, 59 59 00:01:55,370 --> 00:01:57,140 and that's how we're going to answer this question, 60 60 00:01:57,140 --> 00:02:00,070 so, first, we're going to take it step by step. 61 61 00:02:00,070 --> 00:02:01,980 Again, you've memorized your table, 62 62 00:02:01,980 --> 00:02:03,920 so this is going to be a pretty simple problem, 63 63 00:02:03,920 --> 00:02:05,810 because we don't have to do the two to the S, 64 64 00:02:05,810 --> 00:02:07,940 or the two to the H minus two calculations, 65 65 00:02:07,940 --> 00:02:10,730 because we already have all that done in our table here. 66 66 00:02:10,730 --> 00:02:13,140 Now, we're going to round up our department numbers 67 67 00:02:13,140 --> 00:02:16,270 into multiples of two, or factors of two. 68 68 00:02:16,270 --> 00:02:19,570 So, it's either going to be a one, a two, a four, an eight, 69 69 00:02:19,570 --> 00:02:21,140 a 16, a 32, 70 70 00:02:21,140 --> 00:02:23,030 64, or 128. 71 71 00:02:23,030 --> 00:02:24,290 Now, remember for each of these, 72 72 00:02:24,290 --> 00:02:26,560 I told you how many clients needed to be on the network. 73 73 00:02:26,560 --> 00:02:30,040 For example, I say I had 54 people that work in IT, 74 74 00:02:30,040 --> 00:02:32,940 but, you need to still account for the network address, 75 75 00:02:32,940 --> 00:02:35,690 and the broadcast address, for each of those networks. 76 76 00:02:35,690 --> 00:02:38,010 That's always going to be your first and last IP. 77 77 00:02:38,010 --> 00:02:39,160 A lot of students forget that, 78 78 00:02:39,160 --> 00:02:41,050 and they mess up the problems that way. 79 79 00:02:41,050 --> 00:02:43,330 So, if I had 54, what do I need? 80 80 00:02:43,330 --> 00:02:45,040 I really need 56. 81 81 00:02:45,040 --> 00:02:45,873 Now, if I move that up 82 82 00:02:45,873 --> 00:02:48,490 to the next closest range of two to the something power, 83 83 00:02:48,490 --> 00:02:50,050 I get up to 64. 84 84 00:02:50,050 --> 00:02:51,760 So, if I look at IT, 85 85 00:02:51,760 --> 00:02:55,200 I'm going to end up having 64 IP's for that subnet, 86 86 00:02:55,200 --> 00:02:57,470 and we have to figure out the slash notation for it. 87 87 00:02:57,470 --> 00:03:00,330 If I look at the instructors, we had 32 instructors, 88 88 00:03:00,330 --> 00:03:03,360 and we had to get two more, which puts us at 34, 89 89 00:03:03,360 --> 00:03:06,710 which, rounding up, would get me back up to 64, 90 90 00:03:06,710 --> 00:03:08,050 the same as IT. 91 91 00:03:08,050 --> 00:03:09,520 Notice that trick there, 92 92 00:03:09,520 --> 00:03:12,020 I would expect to see something like that on the exam, 93 93 00:03:12,020 --> 00:03:13,150 where they put, it's something, 94 94 00:03:13,150 --> 00:03:15,550 where they tell you I need 16, or 32, 95 95 00:03:15,550 --> 00:03:17,100 because that looks like you'd just be able 96 96 00:03:17,100 --> 00:03:18,670 to give them that slash notation, 97 97 00:03:18,670 --> 00:03:20,970 but if you forget that first and last, 98 98 00:03:20,970 --> 00:03:23,080 you're going to mess that up, so don't do that, right? 99 99 00:03:23,080 --> 00:03:24,530 Make sure you pay attention. 100 100 00:03:24,530 --> 00:03:26,090 Now, the next one we had is sales, 101 101 00:03:26,090 --> 00:03:27,890 and for sales, there was five people, 102 102 00:03:27,890 --> 00:03:30,030 so you add two to that, and that gives me seven, 103 103 00:03:30,030 --> 00:03:30,863 and now, I look in and go, 104 104 00:03:30,863 --> 00:03:32,320 "Oh, seven is close to eight, 105 105 00:03:32,320 --> 00:03:33,930 so that's going to be eight people." 106 106 00:03:33,930 --> 00:03:36,330 Next, we're going to look at admin or administration. 107 107 00:03:36,330 --> 00:03:37,810 Administration has three people, 108 108 00:03:37,810 --> 00:03:39,460 plus two more gets me to five, 109 109 00:03:39,460 --> 00:03:41,680 round that up, that gets me to eight as well. 110 110 00:03:41,680 --> 00:03:43,560 And so, that's the way we do this, right? 111 111 00:03:43,560 --> 00:03:46,740 Now, lastly, I have to calculate the unused amount. 112 112 00:03:46,740 --> 00:03:48,460 Now, this is going to be a little bit different, 113 113 00:03:48,460 --> 00:03:49,750 because instead of rounding up, 114 114 00:03:49,750 --> 00:03:51,340 we're going to have to actually round down. 115 115 00:03:51,340 --> 00:03:52,220 So, first, we're going to start 116 116 00:03:52,220 --> 00:03:54,000 with the total number of IP's that we had, 117 117 00:03:54,000 --> 00:03:56,060 and we were given a slash 24 subnet, 118 118 00:03:56,060 --> 00:03:59,280 so that means we had 256 total IP's. 119 119 00:03:59,280 --> 00:04:01,970 Then, I'm going to take away the 64 I had for IT, 120 120 00:04:01,970 --> 00:04:04,380 and, the 64 I had for instructors, 121 121 00:04:04,380 --> 00:04:06,340 then I'm going to take away the eight I had for sales, 122 122 00:04:06,340 --> 00:04:08,300 and the eight I had for administration. 123 123 00:04:08,300 --> 00:04:11,000 And what I get left is 112 left, 124 124 00:04:11,000 --> 00:04:12,950 but, I can't round up here, 125 125 00:04:12,950 --> 00:04:15,060 because I'm talking about what was left. 126 126 00:04:15,060 --> 00:04:18,000 So, I have to round down to the closest power of two, 127 127 00:04:18,000 --> 00:04:20,510 which, in our case, is going to be a 64 again. 128 128 00:04:20,510 --> 00:04:22,800 So, while this problem originally looked really tough, 129 129 00:04:22,800 --> 00:04:23,700 it really isn't, 130 130 00:04:23,700 --> 00:04:25,800 because we only have to calculate two things. 131 131 00:04:25,800 --> 00:04:28,700 We need to figure out what's the CIDR notation for 64, 132 132 00:04:28,700 --> 00:04:30,330 because that's what we're going to use for IT, 133 133 00:04:30,330 --> 00:04:31,870 the instructors, and unused. 134 134 00:04:31,870 --> 00:04:33,810 And then, we had sales and administration 135 135 00:04:33,810 --> 00:04:34,780 that each had eight, 136 136 00:04:34,780 --> 00:04:37,160 so I need to figure out the CIDR notation for eight. 137 137 00:04:37,160 --> 00:04:39,110 And so, if I figure those two out, it's pretty easy, 138 138 00:04:39,110 --> 00:04:40,600 and I have my chart, 139 139 00:04:40,600 --> 00:04:44,180 so if I look there for 64, that's a slash 26. 140 140 00:04:44,180 --> 00:04:45,550 So, if I have slash 26, 141 141 00:04:45,550 --> 00:04:48,907 that's going to give me 64 for the instructors, 64 for IT, 142 142 00:04:48,907 --> 00:04:50,950 and 64 for the unused. 143 143 00:04:50,950 --> 00:04:53,050 Then, I have sales, which had eight, 144 144 00:04:53,050 --> 00:04:54,920 and that's going to be a slash 29. 145 145 00:04:54,920 --> 00:04:58,000 And administration again is eight, so that's a slash 29. 146 146 00:04:58,000 --> 00:05:00,190 As you can see, this really complex problem 147 147 00:05:00,190 --> 00:05:03,580 became really easy, as we broke it down step-by-step. 148 148 00:05:03,580 --> 00:05:04,960 All right, for our next question, 149 149 00:05:04,960 --> 00:05:06,850 we're going to make it a little bit simpler. 150 150 00:05:06,850 --> 00:05:08,160 The last one may have been something 151 151 00:05:08,160 --> 00:05:11,350 you might see in more or less of a simulation or a PDQ. 152 152 00:05:11,350 --> 00:05:13,200 We have to calculate lots of different things, 153 153 00:05:13,200 --> 00:05:14,590 and then pick the right ones. 154 154 00:05:14,590 --> 00:05:17,680 But, during the test itself, it's going to be multiple choice. 155 155 00:05:17,680 --> 00:05:18,610 So, you're going to get a problem 156 156 00:05:18,610 --> 00:05:20,410 that looks something more like this. 157 157 00:05:20,410 --> 00:05:22,990 Let's say, how many assignable IP addresses exist 158 158 00:05:22,990 --> 00:05:27,990 in the network of 172.16.1.0/27? 159 159 00:05:28,290 --> 00:05:30,550 Now, before we answer this, let me ask you this. 160 160 00:05:30,550 --> 00:05:33,070 Does it even matter what the IP address is? 161 161 00:05:33,070 --> 00:05:34,570 No, it really doesn't. 162 162 00:05:34,570 --> 00:05:37,990 The only thing that matters here is that this is a slash 27. 163 163 00:05:37,990 --> 00:05:40,820 The IP address itself is just there to mess with you, 164 164 00:05:40,820 --> 00:05:43,180 so, you can ignore it in this particular problem. 165 165 00:05:43,180 --> 00:05:45,400 The question becomes how many assignable IP's 166 166 00:05:45,400 --> 00:05:48,360 are there in a network that uses a slash 27? 167 167 00:05:48,360 --> 00:05:51,110 Well, I'm going to have to think about that here for a second. 168 168 00:05:51,110 --> 00:05:52,730 Oh, wait, I really don't have to think about too hard, 169 169 00:05:52,730 --> 00:05:54,260 'cause I have my chart, right? 170 170 00:05:54,260 --> 00:05:57,050 Is it 30, 32, 14, or 64? 171 171 00:05:57,050 --> 00:05:58,250 Well, looking at my chart, 172 172 00:05:58,250 --> 00:06:01,510 I know it's either going to be 32, or it's going to be 30, 173 173 00:06:01,510 --> 00:06:04,660 because a slash 27 shows me there's 32 IP's. 174 174 00:06:04,660 --> 00:06:06,440 Now, which one is it? 175 175 00:06:06,440 --> 00:06:08,400 The keyword here is assignable. 176 176 00:06:08,400 --> 00:06:11,240 The question said how many assignable IP's. 177 177 00:06:11,240 --> 00:06:14,360 Assignable IP means that I can give it to a client. 178 178 00:06:14,360 --> 00:06:16,200 I can assign it to a computer. 179 179 00:06:16,200 --> 00:06:17,810 I can't give away my network ID, 180 180 00:06:17,810 --> 00:06:19,900 and I can't give away my broadcast ID. 181 181 00:06:19,900 --> 00:06:21,930 So, out of those 32 in the subnet, 182 182 00:06:21,930 --> 00:06:24,600 I only have 30 that are assignable. 183 183 00:06:24,600 --> 00:06:26,800 And so, my answer here is 30. 184 184 00:06:26,800 --> 00:06:29,640 Now, even if you couldn't remember that, using your chart, 185 185 00:06:29,640 --> 00:06:32,280 you'd still get it down to either of those two options, 186 186 00:06:32,280 --> 00:06:35,620 30 or 32, and you have a 50/50 shot of guessing right. 187 187 00:06:35,620 --> 00:06:37,170 So, even if you couldn't remember, 188 188 00:06:37,170 --> 00:06:39,330 the fact that you have the network and broadcast ID, 189 189 00:06:39,330 --> 00:06:40,300 which I really hope you do, 190 190 00:06:40,300 --> 00:06:41,520 because I've been beating that into your head 191 191 00:06:41,520 --> 00:06:42,720 a couple of times now, 192 192 00:06:42,720 --> 00:06:45,140 you still would at least get a 50/50 shot on this. 193 193 00:06:45,140 --> 00:06:47,290 Now, let's assume you forgot to write down your chart. 194 194 00:06:47,290 --> 00:06:50,350 How could you calculate this using your subnetting formulas? 195 195 00:06:50,350 --> 00:06:52,890 Well, we would do two to the H minus two. 196 196 00:06:52,890 --> 00:06:55,390 And that's going to give you your number of usable hosts. 197 197 00:06:55,390 --> 00:06:58,210 Since we had slash 27 as our CIDR notation, 198 198 00:06:58,210 --> 00:06:59,280 it becomes, 199 199 00:06:59,280 --> 00:07:02,360 32 minus 27, giving me the number of host bits, 200 200 00:07:02,360 --> 00:07:03,440 which is five. 201 201 00:07:03,440 --> 00:07:06,380 So, two to the number of host bits, two to the fifth, 202 202 00:07:06,380 --> 00:07:10,640 is going to give me 32 minus two, gets me back down to 30. 203 203 00:07:10,640 --> 00:07:12,380 Now, whether you want to do it from the formula, 204 204 00:07:12,380 --> 00:07:15,070 which is a lot more work, or memorizing my table, 205 205 00:07:15,070 --> 00:07:16,780 either way will get you to the right answer 206 206 00:07:16,780 --> 00:07:20,220 of 30 usable IP's, or 30 assignable IP's. 207 207 00:07:20,220 --> 00:07:21,440 Now, just remember, 208 208 00:07:21,440 --> 00:07:24,510 are they asking about assignable or usable IP's? 209 209 00:07:24,510 --> 00:07:26,810 Or, are they asking about total IP's? 210 210 00:07:26,810 --> 00:07:29,360 Depending on how the wording is in the question, 211 211 00:07:29,360 --> 00:07:32,200 that's going to determine, if you're going to minus two or not. 212 212 00:07:32,200 --> 00:07:35,030 If they said, "how many total IP's exist in this network?", 213 213 00:07:35,030 --> 00:07:36,810 the answer would have been 32, 214 214 00:07:36,810 --> 00:07:38,870 but because they use the word assignable, 215 215 00:07:38,870 --> 00:07:41,270 you have to take into account the network ID, 216 216 00:07:41,270 --> 00:07:42,860 and the broadcast ID. 217 217 00:07:42,860 --> 00:07:43,860 And this is going to make sure 218 218 00:07:43,860 --> 00:07:45,400 that you get to the right answer. 219 219 00:07:45,400 --> 00:07:48,060 Now, let's go ahead and look at our third practice problem. 220 220 00:07:48,060 --> 00:07:50,700 How many assignable IP's exist in the network? 221 221 00:07:50,700 --> 00:07:55,700 If I have a network of 192.168.1.0/28, 222 222 00:07:55,810 --> 00:07:57,840 this is just like the last problem. 223 223 00:07:57,840 --> 00:08:00,190 If it's slash 28, we're going to look at our chart, 224 224 00:08:00,190 --> 00:08:03,130 and come up with 16, but they said assignable, 225 225 00:08:03,130 --> 00:08:04,310 so we take off two, 226 226 00:08:04,310 --> 00:08:06,350 one for the network, one for the broadcast, 227 227 00:08:06,350 --> 00:08:08,010 and this gives us 14. 228 228 00:08:08,010 --> 00:08:11,733 And so, our answer is 16 minus two, which gives us 14.