In the previous video, we already learn how to find the best prefix we can use in the 2
computer network. 3
Here we have 100 computers, and we know from the previous video that the best prefix for 4
100 computers is /25. 5
Now, in this video, we are going to determine which IP Address we will use. 6
In the previous video, I also already tell you about Public and Private IP Address. 7
And we need to remember that we must use Private IP Address in the local network. 8
Here is the range of Private IP Address, we are free to use which range. 9
we can use 10, or 172.16 or 192.168, we can use whatever we want. 10
In this case, I want to use 192.168.0.0. 11
This IP is included in the third range of Private IP Address. 12
Now, remember that we need to pay attention on the last number. 13
The first third number will never change. 14
But the last number will be change. 15
If you remember, the number of IP Address is between 0 until 255. 16
So the last number have a chance to change become 0 until 255. 17
Okay let’s start learning. 18
In this case we will search for several thing. 19
Which is Total IP, Subnetmask, IP Network, IP Broadcast, and IP Range. 20
We will learn about all of this one by one. 21
First let’s search for the total IP. 22
We already learn about this, to find the total IP is 2 to the power of 32 minus prefix, 23
in this case, the prefix is /25, 32 minus 25 is 7, and 2 to the power of 7 is 128. 24
So the total IP for prefix /25 is 128. 25
If you forget about the powers, I recommend you to always write it, so 2 to the power 26
of 1 until 2 to the power of 8. 27
Later, if you get used to this, you will never need to write the powers again. 28
You will able to calculate subnetting without even writing anything. 29
So don’t worry to write everything if you just start learning about computer network. 30
Okay, now we know that the total IP for prefix /25 is 128. 31
Next we are going to find the subnetmask. 32
But before that, we will learn about what is subnetmask first. 33
Actually, the function of subnetmask is same as prefix. 34
Some vendor will need prefix when configure an IP Address, but some vendor will need subnetmask. 35
Let’s say we have mikrotik. 36
In Mikrotik we will need prefix when configuring IP Address. 37
But in cisco, we don’t need prefix, we need subnetmask when configuring IP Address. 38
Another example, in windows, we need subnetmask, but in linux, some times we will use prefix 39
rather than subnetmask. 40
But some time we also use subnetmask in linux. 41
The point is, that the function of subnetmask is same as prefix. 42
Some vendor using prefix, but some vendor using subnetmask. 43
Now let’s see in cisco packet tracer. 44
In the previous video, we already build a simple computer network like this. 45
Let’s take a look again to the PC 0. 46
Go to desktop and then IP Configuration. 47
Here we can see that when we configure an IP Address, we will also need to configure 48
subnetmask. 49
But here we don’t see any field to put prefix. So in this case, we will need subnetmask instead 50
of prefix. 51
Okay, now you understand what is subnetmask. 52
Next, let’s calculate subnetmask for prefix /25. 53
The formula is 256 minus by Total IP. 54
In this case, the total IP is 128. 55
So 256 minus 128, the answer is 128. 56
If we see in the cisco packet tracer again, the subnetmask is contains of 4 part of numbers. 57
In this case the subnetmask is 255.255.255.0. 58
Well for prefix /25, we already find that the subnetmask is 128. 59
This 128 is used in the last number of subnetmask. 60
So the subnetmask for prefix /25 is 255.255.255.128. 61
Okay now I hope you understand how to calculate total IP and subnetmask. 62
In the next video, we are going to learn about Network IP, Broadcast IP, and IP Range. 63
Thankyou for watching and see you on the next video!