ccna subnetting

sachinsharma

Hi everyone ,


Could anyone please tell me why do we need to subtract 2 while creating a sunetting like for ex(255.255.255.192=2^6 hosts and no.of subnet are 2^2-2=2)

redgunner

You always need a beginning, a range and an end

Let's look at a very simple to understand network (class c)

Okay let's pick a random host IP!!

Hostname: 192.168.1.64
11000000.10101000.00000001.01000000

Mask: 255.255.255.0
11111111.11111111.11111111.00000000

Let's find our Start Range and End Range (known as subnet and broadcast)
(The bold represents our network portion and the underline represents our host portion)

Subnet: 192.168.1.0
11000000.10101000.00000001.00000000

Broadcast 192.168.1.255
11000000.10101000.00000001.11111111

Okay so the range is 192.168.1.1 to 192.168.254 In this very basic example you can see you have 254 hosts in this 1 subnet.


Let's look another example

Subnet: 192.168.1.0
Mask: 255.255.254.0
Broadcast: 192.168.1.255

So this means you can have a range from 192.168.0.1 - 192.168.1.254 which is 510 hosts
Remember you need a beginning and an end!! (subnet and broadcast)

Imagine it ranging from 192.168.0.1 to 192.168.254.254 (It still only has 1 subnet and 1 broadcast)

Hope this makes sense