-: In this video, I'm going to show you 2 2
how to do subnetting by hand. 3 3
This way, we can eliminate all of the math 4 4
and all of the pen and paper 5 5
and be able to get the answers we need really quickly. 6 6
It's really just a shortcut. 7 7
In the last couple of videos, 8 8
I showed you how everything worked 9 9
so that you understand the theory behind it all, 10 10
but now, we're going to get to the quick way of doing it. 11 11
So, when I subnet by hand to do this demonstration, 12 12
I'm going to wear my subnetting gloves. 13 13
Now, my subnetting gloves are special 14 14
because I have little numbers 15 15
written on the backside of them 16 16
that I'm going to show you here. 17 17
You may see here on my subnetting gloves 18 18
that I have numbers written on them. 19 19
Now, in the real world, you're not going to have your gloves on 20 20
but you can memorize these numbers fairly easily. 21 21
They're just multiples of two. 22 22
Now if I'm going to start on my right, 23 23
which on your screen is going to look like the left, 24 24
you'll see I have two, four, eight, 16, 25 25
32, 64, 128, and 256 written down. 26 26
This tells me how many networks there are. 27 27
This goes back to our two to the nth power, 28 28
which was our formula that we used when we did this by hand. 29 29
So, if I asked you if you had a /26 network, 30 30
how many subnets can be put into a /26 31 31
if you were given a /24 to start with? 32 32
Well, if I have a /24 to start with, 33 33
I'm going to start counting up from there. 34 34
So, my first finger is going to be /25 and then /26. 35 35
Since I asked for /26, you can see the number is four. 36 36
Now, we can do it the other way 37 37
and we can go from my left to right. 38 38
In your case, 39 39
it's going to be your right side of the screen to your left. 40 40
And this is going to tell me how many hosts or IPs I can have 41 41
inside of a network. 42 42
So, if I start from the other side 43 43
and I start with a /24, I have 256. 44 44
/25, I have 128. 45 45
If I have a /26, that's 64. 46 46
/27, that's 32. 47 47
/28, that's 16. 48 48
/29, that's eight. 49 49
/30, that's four. 50 50
/31, that's two. 51 51
So, you can see how this works 52 52
going from right to left or left to right 53 53
to be able to figure out how many networks 54 54
or how many IPs are available. 55 55
Now, we're going to do a couple of examples using this method. 56 56
The first one I'm going to use is this one. 57 57
It's 192.168.0.85. 58 58
Now, the numbers really don't matter. 59 59
It's really what's important is that /29 at the end. 60 60
So, if you want to figure out 61 61
how many subnets that were in a /29, 62 62
how would you do that? 63 63
Well, we're going to count up from right to left, 64 64
upwards in the multiples of two. 65 65
So, if I start counting on my fingers, 66 66
I go 25, 26, 27, 28, 29, 67 67
and what's on my 29? 68 68
It's 32. 69 69
There are 32 subnets if I'm using a /29 network 70 70
within a normal class C network. 71 71
Now, if I'm going to look at this from an IP perspective, 72 72
I'm going to do it the other way. 73 73
How many IPs are there in a /29? 74 74
Well, we're going to start with /24, 256. 75 75
/25, 26, 27, 28, 29, 76 76
and there, you'll see I have eight IPs. 77 77
Now, if you remember from our lessons, 78 78
you always have a broadcast 79 79
and you always have a network name. 80 80
So, really, I have six usable IPs for host. 81 81
I have the first IP which is my network 82 82
and my last IP which is my broadcast, 83 83
giving us a total of eight. 84 84
Again, that's at /29, that's eight. 85 85
The next problem we have is 192.168.1.25 /28. 86 86
So, from doing /28, how many subnets and how many IPs? 87 87
Well, let's pull out our gloves again and we'll start. 88 88
We have /25, /26, /27, /28, 89 89
and the /28 has 16 on it. 90 90
Now, if I go the other way for how many IPs, 91 91
I'm going to go /24, /25, /26, /27, /28. 92 92
It's also 16. 93 93
So, we have 16 subnets and 16 available IPs. 94 94
You could see how this works. 95 95
It makes it really easy. 96 96
So, I think you're getting the idea here 97 97
but let's try two more. 98 98
This next one has a /30. 99 99
So, how many subnets and how many IPs? 100 100
Well, let's pull out our gloves again 101 101
and so, we have /25, /26, /27, 28, 29, and 30, 102 102
and on 30, you see 64 because we counted up, 103 103
two, four, eight, 16, 32, 64. 104 104
And so, by doing that, 105 105
we now know we have 64 subnets. 106 106
That's what a /30 is. 107 107
I could take 256 IPs in a class C 108 108
and I could break it up 64 different times. 109 109
Now, how many IPs is that going to be? 110 110
Well, that's 256 divided by 64 111 111
but if we use our gloves, we can go the other way, 112 112
24, 25, 26, 27, 28, 29, 30, and it's four, four IPs. 113 113
Because we have four IPs and 64 subnets, 114 114
that's going to give us 256 total. 115 115
Let's try another one. 116 116
This one's going to be a /31. 117 117
Now, a /31, that's not even on the table 118 118
you told me to memorize, Jason. 119 119
That's right. 120 120
That's because it's a nonstandard one 121 121
but Cisco does support it. 122 122
It's usually used for point-to-point connections. 123 123
So, if I'm going to connect one router to another router 124 124
and I don't need to have a network 125 125
and a broadcast in that case with Cisco devices, 126 126
I can use a /31 so I'll only use two IPs 127 127
instead of the four that we had in the last /30 example 128 128
which is normally used for point-to-point. 129 129
But again, if we pull out our hands, 130 130
we could start going 131 131
and figuring out how many subnets and how many IPs. 132 132
So, let's do that. 133 133
/25, 26, 27, 28, 29, 30, 31, 134 134
so, that tells me it's on my seventh finger. 135 135
So, if I didn't have my gloves on, 136 136
I would just do powers of two. 137 137
Two, four, eight, 16, 32, 64, 128, 138 138
and so, that seventh finger is 128. 139 139
There's 128 subnets. 140 140
Now, I'm sure you can do the math here. 141 141
If there's 256 total IPs in a class C 142 142
and we just took up 128 subnets, 143 143
that means, there's going to be two IPs per subnet. 144 144
So, let's do it with our hands anyway 145 145
just because that's what we're doing in this video 146 146
and so, here we go. 147 147
We're going to go 24, 25, 26, 27, 28, 29, 30, and 31, 148 148
and on 31, we have a two, right? 149 149
We can do that if we went and counted up or counted down. 150 150
256, 128, 64, 32, 16, eight, four, and two, 151 151
and that gets us to that same number of two. 152 152
So, it's all about memorizing these multiples of two 153 153
as we go through this. 154 154
Again, a /31 is something that's Cisco supported. 155 155
Some of the other routers are starting to support it 156 156
but it is something that is mainly a Cisco thing. 157 157
Let's go ahead and do one last one here 158 158
and this one is going to be a /32. 159 159
So, when we're doing a /32, 160 160
you may go do I even need to use my hands? 161 161
Well, you really don't 162 162
because a /32 just denotes a single host. 163 163
If I have your IP address and put /32, 164 164
it means it's only that IP 165 165
and so, that really is just one IP 166 166
and there can be 256 subnets. 167 167
But if you wanted to use your hands, 168 168
you could do that, right? 169 169
Because we have 25, 26, 27, 28, 29, 30, 31, and 32, 170 170
and you see on 32 it's 256. 171 171
I think you get the idea here. 172 172
So, this is how you can do this 173 173
in a very quick and easy manner. 174 174
Now, before we finish this video, 175 175
I do want to put this to practice 176 176
to some of the things you're going to see on the Network+ exam 177 177
because you're likely not going to get a question 178 178
that just says how many subnets or how many IPs. 179 179
It's going to be a little bit more complicated than that. 180 180
So, let's go to the next question 181 181
and you're going to be able to see what we have. 182 182
So, in this case, I have 171.129.67.160 /25 183 183
and the question I have for you is, 184 184
what's the network IP? 185 185
What's the first host? 186 186
What's the last host? 187 187
And what's the broadcast? 188 188
So, let's pull out our gloves and take a look at this. 189 189
So, if I pull out my gloves and I go for the first one, 190 190
a /25 is two subnets. 191 191
Now, with two subnets, 192 192
that means if I'm using 256 IPs, 193 193
remember, I told you on the Network+ exam, 194 194
we're always going to assume that we're doing this 195 195
in terms of a /24 or greater 196 196
because that's usually what you're going to see on the exam. 197 197
So, in this case, we're going to start with /24, is 256 IPs. 198 198
Because this is a /25, I'm going to have two subnets. 199 199
So, I take that 256 and I break it in half, right? 200 200
So, if I have two subnets, what's the first subnet going to be? 201 201
Well, it's going to start at .0. 202 202
What's the second subnet going to be? 203 203
It's going to start at 128 because we have 128 IPs. 204 204
So, the first one goes from zero to 127 205 205
and the second one is going to go from 128 to 255, 206 206
which gives us our network ID. 207 207
Our network ID is 171.129.67.128 208 208
and our broadcast ID is going to be .255. 209 209
So, what's our first host and our last host? 210 210
Well, it's going to be .29 211 211
and our last host is going to be .254 212 212
because our first host is always 213 213
one above what the network was 214 214
and our last host is always 215 215
one below what the broadcast was. 216 216
That's how this works 217 217
when you're just doing it with your hands. 218 218
It makes it very quick and easy. 219 219
Let's try another one. 220 220
The next one we have is 56.187.210.21 /28. 221 221
So, if I want to take a /28, 222 222
we want to ask how many subnets and how many IP addresses 223 223
cause that's going to help us 224 224
write down what our network and broadcast are 225 225
and that helps us figure out 226 226
our first host and our last host. 227 227
So, if we have a /28, we'll pull out our gloves 228 228
and we'll go 25, 26, 27, 28, 229 229
and 28 is my pinky which is a 16 so there are 16 subnets. 230 230
Now, if I go the other way, how many IPs are there? 231 231
Well, 24, 25, 26, 27, 28. 232 232
There's also 16 IPs. 233 233
So, 16 IPs and 16 subnets. 234 234
Now, if you take those 16 IPs, 235 235
you're going to go zero through 15, that's the first range, 236 236
16 through 31, that's the second range. 237 237
If we look at our IP address we were given, 238 238
it ended in .21. 239 239
Where does that fall? 240 240
Well, it falls in that second range from 16 to 31. 241 241
So, our network is 56.187.210.16. 242 242
Our broadcast is 56.187.210.31. 243 243
And then, we take our last host, 244 244
which is one less than the broadcast .30, 245 245
and our first host, one more than the network .17. 246 246
That's how we can do this 247 247
just using our hands with no pen and paper 248 248
and we can get these answers very quickly as we go through. 249 249
I hope this subnetting by hand was helpful 250 250
and if you didn't get it the first time, 251 251
go ahead and rewatch the video again cause once it clicks, 252 252
it makes all of your subnetting problems so easy 253 253
and so quick to get through 254 254
and you'll have no issues on the Network+ exam.