1 00:00:07,260 --> 00:00:12,180 OK, so in the last lecture, we talked about converting IP addresses into binary. 2 00:00:12,690 --> 00:00:17,640 So the reason we do that is so that you can think about a layer three address in the same way that a 3 00:00:17,640 --> 00:00:24,180 computer thinks about the way we address computers, see bits and binary humanzee decimals and words. 4 00:00:24,660 --> 00:00:28,380 So this is really the first step into understanding something. 5 00:00:28,700 --> 00:00:32,990 Now we're going to really put your newfound knowledge to work. 6 00:00:33,540 --> 00:00:39,990 So let's go ahead and open the command prompt and take a look at the IP address so you can see here 7 00:00:40,110 --> 00:00:43,650 I changed it to 10 that we got five to thirty four. 8 00:00:44,340 --> 00:00:48,540 Subnet mask is now 255 1855 activity to that zero. 9 00:00:49,080 --> 00:00:50,410 This is what we're going to do, right. 10 00:00:50,430 --> 00:00:56,340 I'm going to show you how you can determine which subnet or VLAN a particular host is sitting on right 11 00:00:56,340 --> 00:00:56,610 now. 12 00:00:57,150 --> 00:01:02,520 And you're also going to learn in the next lecture how you can calculate the total number of hosts that 13 00:01:02,520 --> 00:01:03,980 might be assigned to that subnet. 14 00:01:04,200 --> 00:01:06,660 So, you know, why would you want to do this? 15 00:01:06,660 --> 00:01:06,760 Why? 16 00:01:06,830 --> 00:01:07,620 Why does this matter? 17 00:01:07,620 --> 00:01:12,240 Because when you're thinking about scanning a billion or running an attack, you need to know what you're 18 00:01:12,240 --> 00:01:12,740 up against. 19 00:01:13,110 --> 00:01:13,410 Right. 20 00:01:13,410 --> 00:01:17,280 And this will help you get a better view of the lay of the land. 21 00:01:17,580 --> 00:01:17,970 All right. 22 00:01:17,980 --> 00:01:22,280 So first thing we want to do is just draw a little chart first. 23 00:01:22,290 --> 00:01:27,750 We're just going to create a couple of rows in the first row, which is going to represent the values 24 00:01:27,750 --> 00:01:30,660 of the interesting octet in your subnet mask. 25 00:01:31,440 --> 00:01:33,960 OK, so in other words, you have the octet. 26 00:01:34,650 --> 00:01:39,170 This is going to represent the octet where the bits are changing from one to zeros. 27 00:01:39,690 --> 00:01:42,870 So you have that transition from consecutive months, two consecutive zeros. 28 00:01:43,380 --> 00:01:48,930 And we're just going to zoom in on that decimal value for that mask and then analyze the bit positions. 29 00:01:48,960 --> 00:01:50,280 So let me show you what I'm talking about. 30 00:01:51,030 --> 00:01:51,930 We have 128. 31 00:01:53,410 --> 00:01:55,740 Right, then we have 192. 32 00:01:57,920 --> 00:01:58,760 224. 33 00:02:01,050 --> 00:02:04,080 To 40 to 48. 34 00:02:06,340 --> 00:02:13,420 Two fifty two and two fifty five, one, two, three, four, five, six, seven, a missing one. 35 00:02:13,570 --> 00:02:14,640 Oh I forgot to four. 36 00:02:15,190 --> 00:02:20,320 Let's go back to fifty four to fifty five. 37 00:02:20,440 --> 00:02:23,410 So these are subnet mask values that we're looking at right here. 38 00:02:24,110 --> 00:02:28,900 OK, and now we're going to try to position values underneath that. 39 00:02:29,290 --> 00:02:31,930 And I'm going to do is double one starting from the right side? 40 00:02:31,930 --> 00:02:35,710 I'm going to double the number one until I get all the way to the leftmost position. 41 00:02:36,190 --> 00:02:37,600 And I'm going explain what this means. 42 00:02:37,840 --> 00:02:38,410 Don't worry. 43 00:02:38,440 --> 00:02:41,710 But these are the position values also known as the block sizes. 44 00:02:42,470 --> 00:02:46,450 I started one top of one to two squared is four. 45 00:02:48,010 --> 00:02:57,160 And you can see this to the four is eight to the five is 16, and just keep on going 128. 46 00:02:59,350 --> 00:03:04,960 OK, so we have the mask values on the top, we got the block sizes on the bottom, and then we're going 47 00:03:04,960 --> 00:03:07,110 to have a section for the current bit positions. 48 00:03:07,480 --> 00:03:11,880 So let's review something really fast is what we're up against, right? 49 00:03:12,100 --> 00:03:24,820 10 dot three dot five dot thirty four and Damascus 255 dot 255 dot 252 that zero. 50 00:03:25,120 --> 00:03:25,450 Right. 51 00:03:26,200 --> 00:03:29,440 So what this means is that these first two bits. 52 00:03:29,950 --> 00:03:31,060 These first two octets. 53 00:03:32,430 --> 00:03:41,790 It's like that, and the doctor, these are consisting of 16 beds, a here, a here, this ACTTAB has 54 00:03:41,790 --> 00:03:43,420 a mix of ones and zeros. 55 00:03:43,420 --> 00:03:44,820 So it's not exactly 60 Minutes. 56 00:03:45,510 --> 00:03:52,270 So if we know that we start with 16 bits here, we can then zoom in and change the color a little bit. 57 00:03:52,860 --> 00:04:00,720 We can then zoom in from that third octet and look at this expanded position sort of layout for it. 58 00:04:01,170 --> 00:04:02,460 OK, so we've got 16 minutes. 59 00:04:03,180 --> 00:04:13,050 And if we want to keep counting until we get until 20 to 17, 18, 19, 20, 21, 22. 60 00:04:13,500 --> 00:04:18,350 So you can see that when we get to 250 to see, we've counted 22 bits. 61 00:04:18,750 --> 00:04:20,860 OK, so we're going to call that a 22. 62 00:04:21,690 --> 00:04:22,060 All right. 63 00:04:22,320 --> 00:04:24,900 So again, these are the mask values up here. 64 00:04:25,800 --> 00:04:27,510 These are the block sizes. 65 00:04:28,350 --> 00:04:36,210 And the bit positions would be one, two, three, four, five, six. 66 00:04:36,840 --> 00:04:37,140 Right. 67 00:04:37,410 --> 00:04:40,990 Because this number 252 and you break down the number of bits. 68 00:04:41,640 --> 00:04:42,480 This is what equals. 69 00:04:42,480 --> 00:04:43,080 How do I know? 70 00:04:43,080 --> 00:04:48,360 Because 128 plus 64 plus 32 for 16 plus eight plus four equals 252. 71 00:04:48,550 --> 00:04:50,970 So that's why we have 22 consecutive bits. 72 00:04:50,970 --> 00:04:52,290 And that's the subnet mask here. 73 00:04:53,040 --> 00:04:54,760 These last two bits are zero. 74 00:04:54,780 --> 00:04:55,950 So these are the big positions. 75 00:04:56,570 --> 00:05:02,940 Now, this is where things get a little bit messy because in order to determine the network we're on, 76 00:05:02,940 --> 00:05:09,660 we need to get that block size in the way we get the block size is we look at the rightmost bit of the 77 00:05:09,660 --> 00:05:10,140 mask. 78 00:05:11,210 --> 00:05:21,990 So let me just clear things up a little bit to make more sense of this to 55 to 45 to 50 to zero. 79 00:05:22,440 --> 00:05:28,050 This is one, two, three, four, five, six, seven, eight, five, six, seven, eight, one, two, 80 00:05:28,050 --> 00:05:29,870 three, four, five, six, seven, eight. 81 00:05:30,540 --> 00:05:30,780 Right. 82 00:05:31,350 --> 00:05:37,500 So the rightmost bit the third octet is the interesting octet where they 021 transition happens. 83 00:05:38,130 --> 00:05:39,300 The rightmost bit is this one. 84 00:05:39,810 --> 00:05:41,190 And if you remember, you may not. 85 00:05:41,190 --> 00:05:50,460 But from that previous screen, when you looked at all the enmasse values, we had 128, 192, 224, 86 00:05:51,300 --> 00:05:52,960 240, and you should write these out every time. 87 00:05:52,960 --> 00:05:54,330 It's really good to memorize these. 88 00:05:57,190 --> 00:06:00,250 Fifty two to fifty four to fifty five. 89 00:06:00,730 --> 00:06:06,780 And if you look at this, so you have eight here, get it here that 16, 17, 18, 19, 20, 21, 22, 90 00:06:07,530 --> 00:06:09,270 22, like 22 here. 91 00:06:09,960 --> 00:06:11,960 This equals this, OK? 92 00:06:12,780 --> 00:06:20,460 And if you look at the rightmost bit of the mask, this one right here, this is actually in the one 93 00:06:20,460 --> 00:06:32,300 two four eight 16, 32, 64, 128 252 is in this position, the number four position. 94 00:06:32,580 --> 00:06:32,910 Right. 95 00:06:33,240 --> 00:06:34,890 So number four is the block size. 96 00:06:35,220 --> 00:06:36,310 That's the main thing I want you to see. 97 00:06:36,660 --> 00:06:39,330 And so now that we have the block size, this is where we do the math. 98 00:06:40,710 --> 00:06:42,230 So we know the block size is a four. 99 00:06:43,530 --> 00:06:44,130 What do we do with it? 100 00:06:44,500 --> 00:06:56,400 We can do is we take the last network octet value of the IP 10 dot three dot five dot 34, last network 101 00:06:56,400 --> 00:07:03,330 octet value of this IP is this five adelines up from the mask is what shows you the network portion. 102 00:07:03,960 --> 00:07:06,150 Clearly the ten is in the network portion section. 103 00:07:06,150 --> 00:07:11,040 The three that the network portion because of the 255 255 for the ten fifty five for the three and there's 104 00:07:11,040 --> 00:07:11,700 252. 105 00:07:11,790 --> 00:07:12,990 That's also the network portion. 106 00:07:13,560 --> 00:07:15,760 It's in the third octet for this five. 107 00:07:15,810 --> 00:07:21,360 So what we do is we take that five and we divide it by the block side the four. 108 00:07:21,880 --> 00:07:27,100 So when we take five divided by four, we're going to get one point something. 109 00:07:27,630 --> 00:07:28,680 All we care about is the one. 110 00:07:30,120 --> 00:07:30,480 That's it. 111 00:07:31,410 --> 00:07:32,400 We don't care about the remainder. 112 00:07:32,400 --> 00:07:33,150 We just need the number. 113 00:07:33,990 --> 00:07:41,550 And then once we have that number, we multiply this number by the block size and one times four is 114 00:07:41,550 --> 00:07:42,140 equal to four. 115 00:07:42,180 --> 00:07:43,330 That's all the math we need to know. 116 00:07:44,070 --> 00:07:46,070 OK, so I hope that's not too complicated. 117 00:07:46,090 --> 00:07:52,770 OK, it's just a matter of first determining the block size and then taking that block size. 118 00:07:53,130 --> 00:07:59,130 Then it's a matter of taking the the interesting bit in the interesting octet and dividing that by the 119 00:07:59,130 --> 00:08:02,430 block size and taking that result and multiplying it by the block size. 120 00:08:03,120 --> 00:08:04,230 And then you have that number. 121 00:08:04,770 --> 00:08:07,530 Now what you can do is write out your subnets because, you know, now. 122 00:08:09,070 --> 00:08:12,550 Some that ranges, we're not going get into the rain just completely right now, but let me show you 123 00:08:12,550 --> 00:08:15,980 what you know now from this map that we just did what you can do now. 124 00:08:16,000 --> 00:08:17,890 You can take that IP 10. 125 00:08:18,370 --> 00:08:21,540 And as you're writing this out, you know, the block size of the four. 126 00:08:21,880 --> 00:08:23,350 So we're in the third octet. 127 00:08:23,890 --> 00:08:26,290 So you put a four there and then you just put a zero for the hosts. 128 00:08:26,620 --> 00:08:27,760 That's the first network. 129 00:08:28,450 --> 00:08:29,850 The second one would be ten. 130 00:08:30,110 --> 00:08:32,300 Three, eight. 131 00:08:32,480 --> 00:08:33,640 You just add another four. 132 00:08:34,170 --> 00:08:35,320 It's the second network. 133 00:08:35,500 --> 00:08:37,150 And these could be different floors of the same building. 134 00:08:37,150 --> 00:08:38,080 They could be different departments. 135 00:08:38,080 --> 00:08:42,760 They could be different, you know, logical units just depends on how the organization is divided. 136 00:08:43,090 --> 00:08:44,260 But these are different subnets. 137 00:08:46,600 --> 00:08:47,650 You do 12 here, right? 138 00:08:47,920 --> 00:08:48,490 It keeps going. 139 00:08:49,060 --> 00:08:53,230 And the point here now is now that we have these different subnets, we're going to we can basically 140 00:08:53,230 --> 00:09:00,820 see, you know, where our IP address is, because if you look at this, you can see now that we have 141 00:09:01,420 --> 00:09:05,150 10 DOT 4.0 and the next one is ten to zero, what, ten point three to five. 142 00:09:05,740 --> 00:09:09,790 That thirty four fits in between both of these networks. 143 00:09:10,510 --> 00:09:15,480 So we know then that we are on the 10 that we got, that's the zero network, this whole system, that 144 00:09:15,490 --> 00:09:20,970 network, his host is not in the top three eight zero network in the next election to show you how you 145 00:09:20,980 --> 00:09:25,810 can build your ranges and we can actually show your broadcast interests in the network I.D. and all 146 00:09:25,810 --> 00:09:26,380 that good stuff. 147 00:09:26,590 --> 00:09:27,430 I will say that for the next. 148 00:09:27,440 --> 00:09:29,020 Let's see in a second.