Yes, you are right. The fastest way is to use an IP subnet calculator. You can find tons of free IP subnet calculators over the Internet, example like http://www.subnet-calculator.com/
But, what if something happened to your PC, where you can't use the software or internet to do the calculation for you. Therefore, you should always have a backup, like every IT staff did. Make yourself a backup and learn how to count without any 3rd party tools.
Actually is not as difficult as you think. Here, I will show you an easy way to do it.
Given a scenario, if provides you the IP address and subnet mask. And ask you to find out what is the number of valid hosts, subnet and broadcast address.
Example:
IP - 192.168.10.34
subnet mask - 255.255.255.224 or CIDR (Classless Inter-Domain Routing) :/27
To find subnet and broadcast address.
1) 256 - 224(subnet mask last octet) = 32First subnet is 32.
Second subnet is 32 x 2 = 64
Third subnet is 32 x 3 = 96
.
.
.etc
Since our IP (192.168.10.34) is fall between 32 - 64 subnet, so the subnet address is 192.168.10.32 and the broadcast address is 192.168.10.63.
Find Host range
1) Valid hosts range is 192.168.10.33 - 192.168.10.62
- as 192.168.10.32 is subnet, 192.168.10.63 is broadcast
Find total valid hosts
1) 192.168.10.(62) - 192.168.10.(33) = 29
or
32 - 27(CIDR) = 5
2y = 25 - 2
= 31 - 2
= 29
All solution only got 1 step. Simple isn't it. Still don't understand? Nevermind, let's do another example.
202.188.0.50
255.255.255.240 or CIDR = /28
Subnet size: 256-240 = 16
Subnets are : 203.199.10.0, 202.188.0.16, 202.188.0.32, 202.188.0.48, 202.188.0.64
Our IP (.50) fall between 202.188.0.48 and 202.188.0.64 subnet.
Thus, our subnet is 202.188.0.48.
our next subnet is 202.188.0.64,
Thus, our braodcast address is 202.188.0.63
I assume everyone knows we can't assign the network address and broadcast address to any hosts, our valid hosts are between 202.188.0.49 - 202.188.0.63
32 - 28
= 4
24 - 2 = [(2 x 2 x 2 x 2) - 2] = 14
Easy isn't it.
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