Networking – Dividing a network into subnets

ipnetworkingsubnet

I'm finding it very hard to understand IP subnetting.

The things I already know how to do: Given an IP-adres and a subnet mask, I'm able to find all ip adresses in the subnet. Given an ip adres like 145.244.0.0/14, I'm able to find the subnet mask.

The things I don't know how to do is an exercise like this: Dividing a network say 192.168.0/24 into subnets. Each subnet must contain at least 10 hosts. Which are the first seven subnets?

How would I go about finding a solution for such exercise?
I'm supposed to find the Subnet adres, the subnet mask, the first host IP, the last host IP and the broadcast adress.

Note that this isn't some sort of homework, I have the solution in my book, but I don't know where it's coming from.

Thank you for helping me out.

Best Answer

For a question like that, you start by figuring out how many bits you need to cover that many hosts:

10 hosts, 2^4 = 16 (minus 2 for ID and broadcast). 32-4 = 28, so you're going to use a /28 subnet.

Using your knowledge of how to find IPs in the subnet, you can work backwards from here. You can also list out all the subnets by adding 16, or by working backwards from the IPs again:

192.168.0/24 (given supernet)
  192.168.0/28
  192.168.16/28
  192.168.32/28
  192.168.48/28
  192.168.64/28
  ...

Caveat: Most of these training exercises consider the first and last subnets to be unusable, as well as the first and last IP in each subnet. However, there is a slightly nonstandard method allowing their use.

Related Question