1 00:00:00,450 --> 00:00:01,470 In the last lesson, 2 00:00:01,470 --> 00:00:04,140 we covered a lot of details about subnets. 3 00:00:04,140 --> 00:00:05,580 Now what I want to do in this lesson 4 00:00:05,580 --> 00:00:07,590 is take some of these problems and go through them 5 00:00:07,590 --> 00:00:09,780 because you may experience them come test day. 6 00:00:09,780 --> 00:00:11,760 So I want to walk through how to tackle them. 7 00:00:11,760 --> 00:00:13,410 Now before we get to the first problem, 8 00:00:13,410 --> 00:00:14,340 the first thing I want to do 9 00:00:14,340 --> 00:00:16,350 is put my chart back on the screen. 10 00:00:16,350 --> 00:00:17,970 Now, why am I doing this? 11 00:00:17,970 --> 00:00:19,260 Well, because I already told you, 12 00:00:19,260 --> 00:00:21,270 you should commit this chart to memory. 13 00:00:21,270 --> 00:00:23,340 And when you get down and you sit for the exam, 14 00:00:23,340 --> 00:00:24,300 the first thing they're going to do 15 00:00:24,300 --> 00:00:26,490 is give you a piece of paper and a pencil. 16 00:00:26,490 --> 00:00:27,540 And once they start the clock, 17 00:00:27,540 --> 00:00:29,520 you can write whatever you want on that dump sheet. 18 00:00:29,520 --> 00:00:30,840 And so one of the things I put down 19 00:00:30,840 --> 00:00:32,700 on my dump sheet or my note sheet 20 00:00:32,700 --> 00:00:35,460 is that I put down from my memory this chart, 21 00:00:35,460 --> 00:00:38,160 and that way as I get sub in questions throughout the exam, 22 00:00:38,160 --> 00:00:39,810 I can go back and look at those, 23 00:00:39,810 --> 00:00:40,860 and so it makes it really easy. 24 00:00:40,860 --> 00:00:42,360 So I'm going to give it to you here 25 00:00:42,360 --> 00:00:44,910 because I'm assuming you've memorized this before the exam 26 00:00:44,910 --> 00:00:46,380 and you've already written down 27 00:00:46,380 --> 00:00:48,090 as you're sitting at your computer. 28 00:00:48,090 --> 00:00:49,980 All right, let's take our first question: 29 00:00:49,980 --> 00:00:51,630 Let's pretend you're a network administrator 30 00:00:51,630 --> 00:00:53,400 for DionTraining.com. 31 00:00:53,400 --> 00:00:54,690 We decide we're going to open up 32 00:00:54,690 --> 00:00:56,820 a small branch office in another city. 33 00:00:56,820 --> 00:00:59,100 And so to support that I need a subnet 34 00:00:59,100 --> 00:01:01,350 for a private IP address that's given to you 35 00:01:01,350 --> 00:01:04,050 for several different networks based on the different sizes 36 00:01:04,050 --> 00:01:06,330 of the departments in this new location. 37 00:01:06,330 --> 00:01:08,220 Now, the new office has been given the range 38 00:01:08,220 --> 00:01:11,940 of 10.10.10.0/24, 39 00:01:11,940 --> 00:01:15,810 which tells you you have 256 total IPs to work with. 40 00:01:15,810 --> 00:01:17,370 Now, when you set up your new network, 41 00:01:17,370 --> 00:01:19,470 I want you to configure separate subnets 42 00:01:19,470 --> 00:01:21,540 for each of the departments that I'm going to give you. 43 00:01:21,540 --> 00:01:23,760 And you're going to tell me which CIDR notation 44 00:01:23,760 --> 00:01:26,940 is going to be the summary for each one in each place. 45 00:01:26,940 --> 00:01:28,290 Now, I want you to resist the urge 46 00:01:28,290 --> 00:01:30,120 of going big for each subnet. 47 00:01:30,120 --> 00:01:32,550 I want you to tell me the minimum subnet 48 00:01:32,550 --> 00:01:34,680 that would support my requirements. 49 00:01:34,680 --> 00:01:36,120 Now, in my new company, 50 00:01:36,120 --> 00:01:38,640 we're going to have this number of users that we have. 51 00:01:38,640 --> 00:01:41,550 So first I have 54 new people in IT, 52 00:01:41,550 --> 00:01:43,290 I have 32 new instructors, 53 00:01:43,290 --> 00:01:44,940 I have five people in sales, 54 00:01:44,940 --> 00:01:46,350 three in administration, 55 00:01:46,350 --> 00:01:48,990 and then there's going to be an unused portion that's left over 56 00:01:48,990 --> 00:01:51,180 and you're going to gimme a subnet for that as well. 57 00:01:51,180 --> 00:01:52,590 Now, each of these five areas, 58 00:01:52,590 --> 00:01:55,380 I need you to tell me what the CIDR notation is for it, 59 00:01:55,380 --> 00:01:57,150 and that's how we're going to answer this question. 60 00:01:57,150 --> 00:02:00,060 So first, we're going to take it step by step. 61 00:02:00,060 --> 00:02:01,980 Again, you've memorized your table, 62 00:02:01,980 --> 00:02:03,930 so this is going to be a pretty simple problem 63 00:02:03,930 --> 00:02:05,790 because we don't have to do the 2 to the S 64 00:02:05,790 --> 00:02:07,920 or the 2 to the h - 2 calculations 65 00:02:07,920 --> 00:02:10,740 because we already have all that done in our table here. 66 00:02:10,740 --> 00:02:13,170 Now, we're going to round up our department numbers 67 00:02:13,170 --> 00:02:16,290 into multiples of two or factors of two. 68 00:02:16,290 --> 00:02:19,560 So, it's either going to be a 1, a 2, a 4, an 8, 69 00:02:19,560 --> 00:02:23,040 a 16, a 32, 64, or 128. 70 00:02:23,040 --> 00:02:24,300 Now remember for each of these, 71 00:02:24,300 --> 00:02:26,580 I told you how many clients need to be on the network. 72 00:02:26,580 --> 00:02:30,060 For example, I say I had 54 people that work in IT, 73 00:02:30,060 --> 00:02:32,970 but you need to still account for the network address 74 00:02:32,970 --> 00:02:35,700 and the broadcast address for each of those networks, 75 00:02:35,700 --> 00:02:38,010 that's always going to be your first and last IP. 76 00:02:38,010 --> 00:02:39,150 A lot of students forget that 77 00:02:39,150 --> 00:02:41,070 and they mess up the problems that way. 78 00:02:41,070 --> 00:02:43,320 So if I had 54, what do I need? 79 00:02:43,320 --> 00:02:45,060 I really need 56. 80 00:02:45,060 --> 00:02:46,920 Now, if I move that up to the next closest range 81 00:02:46,920 --> 00:02:50,040 of two to the something power, I get up to 64. 82 00:02:50,040 --> 00:02:51,750 So, if I look at IT, 83 00:02:51,750 --> 00:02:55,200 I'm going to end up having 64 IPs for that subnet, 84 00:02:55,200 --> 00:02:57,350 and we have to figure out the slash notation for it. 85 00:02:57,350 --> 00:02:58,770 If I look at the instructors, 86 00:02:58,770 --> 00:03:00,360 we had 32 instructors, 87 00:03:00,360 --> 00:03:03,360 and we had to get two more, which puts us at 34, 88 00:03:03,360 --> 00:03:06,720 which, rounding up, would get me back up to 64, 89 00:03:06,720 --> 00:03:08,040 the same as IT. 90 00:03:08,040 --> 00:03:09,540 Notice that trick there, 91 00:03:09,540 --> 00:03:12,000 I would expect to see something like that on the exam 92 00:03:12,000 --> 00:03:13,620 where they put something where they tell you 93 00:03:13,620 --> 00:03:17,130 I need 16 or 32 because that looks like you'd just be able 94 00:03:17,130 --> 00:03:18,690 to give them that slash notation. 95 00:03:18,690 --> 00:03:20,970 But if you forget that, first and last, 96 00:03:20,970 --> 00:03:21,990 you're going to miss that up. 97 00:03:21,990 --> 00:03:23,070 So don't do that, right? 98 00:03:23,070 --> 00:03:24,540 Make sure you pay attention. 99 00:03:24,540 --> 00:03:26,160 Now the next one we had is sales, 100 00:03:26,160 --> 00:03:27,900 and for sales there was five people. 101 00:03:27,900 --> 00:03:30,060 So you add two to that and that gives me seven. 102 00:03:30,060 --> 00:03:31,230 And now I look at it and go, oh, 103 00:03:31,230 --> 00:03:32,310 seven's close to eight, 104 00:03:32,310 --> 00:03:33,930 so that's going to be eight people. 105 00:03:33,930 --> 00:03:36,300 Next we're going to look at admin or administration. 106 00:03:36,300 --> 00:03:37,800 Administration has three people 107 00:03:37,800 --> 00:03:39,450 plus two more gets me to five. 108 00:03:39,450 --> 00:03:41,730 Round that up, that gets me to eight as well. 109 00:03:41,730 --> 00:03:43,560 And so that's the way we do this, right? 110 00:03:43,560 --> 00:03:46,740 Now lastly, I have to calculate the unused amount. 111 00:03:46,740 --> 00:03:48,450 Now, this is going to be a little bit different 112 00:03:48,450 --> 00:03:49,740 because instead of rounding up, 113 00:03:49,740 --> 00:03:51,360 we're going to have to actually round down. 114 00:03:51,360 --> 00:03:52,230 So first we're going to start 115 00:03:52,230 --> 00:03:54,060 with the total number of IPs that we had 116 00:03:54,060 --> 00:03:56,040 and we were given a /24 subnet. 117 00:03:56,040 --> 00:03:59,280 So that means we had 256 total IPs. 118 00:03:59,280 --> 00:04:01,980 Then I'm going to take away the 64 I had for IT 119 00:04:01,980 --> 00:04:04,410 and the 64 I had for instructors, 120 00:04:04,410 --> 00:04:06,420 then I'm going to take away the eight I had for sales 121 00:04:06,420 --> 00:04:08,310 and the eight I had for administration. 122 00:04:08,310 --> 00:04:11,010 And what I get left is 112 left, 123 00:04:11,010 --> 00:04:12,960 but I can't round up here 124 00:04:12,960 --> 00:04:15,090 because I'm talking about what was left. 125 00:04:15,090 --> 00:04:18,000 So, I have to round down to the closest power of two, 126 00:04:18,000 --> 00:04:20,519 which in our case is going to be a 64 again. 127 00:04:20,519 --> 00:04:22,800 So, while this problem originally looked really tough, 128 00:04:22,800 --> 00:04:23,730 it really isn't 129 00:04:23,730 --> 00:04:25,800 because we only have to calculate two things. 130 00:04:25,800 --> 00:04:28,710 We need to figure out what's the CIDR notation for 64 131 00:04:28,710 --> 00:04:30,330 because that's where we're going to use for IT, 132 00:04:30,330 --> 00:04:31,890 the instructors, and unused. 133 00:04:31,890 --> 00:04:33,810 And then we had sales and administration 134 00:04:33,810 --> 00:04:34,800 that each had eight. 135 00:04:34,800 --> 00:04:37,200 So I need to figure out the CIDR notation for eight. 136 00:04:37,200 --> 00:04:38,370 And so if I figure those two out, 137 00:04:38,370 --> 00:04:40,620 it's pretty easy, and I have my chart. 138 00:04:40,620 --> 00:04:44,190 So if I look there for 64, that's a /26. 139 00:04:44,190 --> 00:04:45,540 So if I have /26, 140 00:04:45,540 --> 00:04:47,970 that's going to gimme 64 for the instructors, 141 00:04:47,970 --> 00:04:50,970 64 for IT, and 64 for the unused. 142 00:04:50,970 --> 00:04:53,040 Then I have sales which had eight, 143 00:04:53,040 --> 00:04:54,930 and that's going to be a /29. 144 00:04:54,930 --> 00:04:57,687 And administration again is eight, so that's a /29. 145 00:04:57,687 --> 00:05:00,210 And so you can see this really complex problem 146 00:05:00,210 --> 00:05:03,570 became really easy as we broke it down step by step. 147 00:05:03,570 --> 00:05:04,950 All right, for our next question, 148 00:05:04,950 --> 00:05:06,840 we're going to make it a little bit simpler. 149 00:05:06,840 --> 00:05:08,730 The last one may have been something you might see 150 00:05:08,730 --> 00:05:11,340 in more or less of a simulation or a PBQ. 151 00:05:11,340 --> 00:05:13,200 We have to calculate lots of different things 152 00:05:13,200 --> 00:05:14,610 and then pick the right ones. 153 00:05:14,610 --> 00:05:16,140 But during the test itself, 154 00:05:16,140 --> 00:05:17,700 it's going to be multiple choice. 155 00:05:17,700 --> 00:05:18,600 So you're going to get a problem 156 00:05:18,600 --> 00:05:20,430 that looks something more like this. 157 00:05:20,430 --> 00:05:22,980 Let's say how many assignable IP addresses exist 158 00:05:22,980 --> 00:05:27,980 in the network of 172.16.1.0/27? 159 00:05:28,290 --> 00:05:30,570 Now, before we answer this, let me ask you this, 160 00:05:30,570 --> 00:05:33,060 does it even matter what the IP address is? 161 00:05:33,060 --> 00:05:34,620 No, it really doesn't. 162 00:05:34,620 --> 00:05:35,910 The only thing that matters here 163 00:05:35,910 --> 00:05:37,980 is that this is a /27. 164 00:05:37,980 --> 00:05:40,830 The IP address itself is just there to mess with you. 165 00:05:40,830 --> 00:05:43,200 So you can ignore it in this particular problem. 166 00:05:43,200 --> 00:05:45,720 The question becomes how many assignable IPs are there 167 00:05:45,720 --> 00:05:48,360 in a network that uses a /27? 168 00:05:48,360 --> 00:05:51,120 Well, I'm going to have to think about that here for a second. 169 00:05:51,120 --> 00:05:52,860 Oh wait, I really don't have to think about it too hard 170 00:05:52,860 --> 00:05:54,270 because I have my chart, right? 171 00:05:54,270 --> 00:05:57,060 Is it 30, 32, 14, or 64? 172 00:05:57,060 --> 00:05:58,260 Well, looking at my chart, 173 00:05:58,260 --> 00:06:01,530 I know it's either going to be 32 or it's going to be 30 174 00:06:01,530 --> 00:06:04,680 because a /27 shows me there's 32 IPs. 175 00:06:04,680 --> 00:06:06,450 Now, which one is it? 176 00:06:06,450 --> 00:06:08,400 The keyword here is "assignable." 177 00:06:08,400 --> 00:06:11,250 The question said how many assignable IPs? 178 00:06:11,250 --> 00:06:14,310 Assignable IPs means that I can give it to a client, 179 00:06:14,310 --> 00:06:16,200 I can assign it to a computer. 180 00:06:16,200 --> 00:06:17,820 I can't give away my network ID 181 00:06:17,820 --> 00:06:19,920 and I can't give away my broadcast ID. 182 00:06:19,920 --> 00:06:22,350 So, out of those 32 in the subnet, 183 00:06:22,350 --> 00:06:24,630 I only have 30 that are assignable. 184 00:06:24,630 --> 00:06:26,790 And so my answer here is 30. 185 00:06:26,790 --> 00:06:28,740 Now, even if you couldn't remember that, 186 00:06:28,740 --> 00:06:30,600 using your chart, you'd still get it down 187 00:06:30,600 --> 00:06:33,554 to either of those two options, 30 or 32, 188 00:06:33,554 --> 00:06:35,640 and you have a 50-50 shot of guessing, right? 189 00:06:35,640 --> 00:06:37,170 So even if you couldn't remember 190 00:06:37,170 --> 00:06:39,360 the fact that you have the network and broadcast ID, 191 00:06:39,360 --> 00:06:40,320 which I really hope you do, 192 00:06:40,320 --> 00:06:41,520 'cause I've been beating that into your head 193 00:06:41,520 --> 00:06:42,720 a couple of times now, 194 00:06:42,720 --> 00:06:45,120 you still would at least get a 50-50 shot on this. 195 00:06:45,120 --> 00:06:47,280 Now, let's assume you forgot to write down your chart, 196 00:06:47,280 --> 00:06:50,370 how could you calculate this using your subnetting formulas? 197 00:06:50,370 --> 00:06:52,920 Well, we would do 2 to the h - 2, 198 00:06:52,920 --> 00:06:55,410 and that's going to give you your number of usable hosts. 199 00:06:55,410 --> 00:06:58,230 Since we had /27 as our CIDR notation, 200 00:06:58,230 --> 00:07:01,080 it becomes 32 - 27, 201 00:07:01,080 --> 00:07:03,450 giving me the number of host bits, which is five. 202 00:07:03,450 --> 00:07:05,340 So, two to the number of host bits, 203 00:07:05,340 --> 00:07:07,890 two to the fifth is going to gimme 32, 204 00:07:07,890 --> 00:07:10,650 minus two gets me back down to 30. 205 00:07:10,650 --> 00:07:12,420 Now whether you want to do it from the formula, 206 00:07:12,420 --> 00:07:15,060 which is a lot more work or memorizing my table, 207 00:07:15,060 --> 00:07:15,960 either way will get you 208 00:07:15,960 --> 00:07:20,250 to the right answer of 30 usable IPs or 30 assignable IPs. 209 00:07:20,250 --> 00:07:21,450 Now just remember, 210 00:07:21,450 --> 00:07:24,510 are they asking about assignable or usable IPs, 211 00:07:24,510 --> 00:07:26,820 or are they asking about total IPs? 212 00:07:26,820 --> 00:07:29,340 Depending on how the wording is in the question, 213 00:07:29,340 --> 00:07:32,190 that's going to determine if you're going to minus two or not. 214 00:07:32,190 --> 00:07:35,010 If they said, "How many total IPs exist in this network," 215 00:07:35,010 --> 00:07:36,810 the answer would've been 32. 216 00:07:36,810 --> 00:07:38,880 But because they used the word "assignable," 217 00:07:38,880 --> 00:07:41,280 you have to take into account the network ID 218 00:07:41,280 --> 00:07:42,870 and the broadcast ID, 219 00:07:42,870 --> 00:07:43,860 and this is going to make sure 220 00:07:43,860 --> 00:07:45,390 that you get to the right answer. 221 00:07:45,390 --> 00:07:48,060 Now, let's go ahead and look at our third practice problem. 222 00:07:48,060 --> 00:07:50,730 How many assignable IPs exist in the network? 223 00:07:50,730 --> 00:07:55,730 If I have the network of 192.168.1.0/28, 224 00:07:55,800 --> 00:07:57,840 this is just like the last problem. 225 00:07:57,840 --> 00:08:00,180 If the /28, we're going to look at our chart 226 00:08:00,180 --> 00:08:01,650 and come up with 16. 227 00:08:01,650 --> 00:08:03,150 But they said assignable, 228 00:08:03,150 --> 00:08:05,190 so we take off two, one for the network, 229 00:08:05,190 --> 00:08:08,040 one for the broadcast, and this gives us 14. 230 00:08:08,040 --> 00:08:11,733 And so our answer is 16 minus 2, which gives us 14.