# what is meaning of sub netting

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#### achuth002

##### Junior Member level 3
how to calculating the sub netting
and what is the use of sub netting

We can divide the net in different small nets. The main idea of subnet is to manage efficiently the IP of the network so we can use the rights IP on all my net.

Imagine this net 192.168.1.0/24.

As you know the last char (0) means 256 hosts (2^8), the 24 means 24 1's of the netmask...
192 . 168 . 1 . 0
<...............><.>
255 . 255 .255. 0

The first part we call it "the network part"
The last one "the hosts part"

But usable host are allways #hosts - 2, because the first one is the network and the last one is the broadcast address, so we have 254 usable hosts.

192.168.1.0 -> not usable (the network address)
192.168.1.1 -> usable
.
.
.

What if we have 26 hosts!?. Using this network we will be wasting IPs, so we will subnet it.
Divide the total hosts by 2!
256/2 = 128
128/2 = 64
64/2 = 32 <--- we will use 32 hosts
32/2 = 16

So count how many times you get divide (3 times), and add to the before explained netmask (24+3) as a result of 27
The net is 192.168.1.0/24 or 192.168.1.0 255.255.255.0
The subnet is 192.168.1.0/27 or 192.168.1.0 255.255.255.224
The total subnet hosts are 32
The usable hosts are 30

So we can start dividing all the net by 32 hosts
192.168.1.0 to 192.168.1.31
192.168.1.32 to 192.168.1.63
192.168.1.64 to 192.168.1.95
192.168.1.96 to 192.168.1.127
192.168.1.128 to 192.168.1.159
192.168.1.160 to 192.168.1.191
192.168.1.192 to 192.168.1.223
192.168.1.224 to 192.168.1.255

We can use any network we want!
I took 192.168.1.192, so i can start assigning IPs to my 26 hosts

192.168.1.192 <- subnet
192.168.1.193 <- first usable ip
.
.
.
192.168.1.222 <- last usable ip

A final tip is if we don't know the subnet or net of the IP 192.168.1.78, we can multiply (booleanly) 78 & 224, that is the mask.

There is more, but hope you understand the basics.

• achuth002

Points: 2