# Assigning subnet masks to subnetworks?

Given network ID and default mask 200.16.27.0/24, how would I assign subnet masks to each of the six subnetworks? I have no idea how to do the work.

### 3 Answers

- BigELv 78 months ago
This sort of misleading, the router links are point to points not hosts. So I consider those to be useable ips, not hosts.

So lets just do that, even though one tends to put the large networks on the low end, one can gather together similar networks if they fill a block.

So a /30, is 2 bits, the last 2, or 4 ips. Since we want to use the last ips, that would be 200.16.27.252/30, spanning 200.16.27.252-255.

The network is 200.16.27.252.

The first router interface is 200.16.27.253/30

The second router interface is 200.16.27.254/30

broadcast is 200.16.27.255

Take each network, see what block you need (how bit a power of 2 you need)

and fit it into a /24, even if you have to draw it out. They can't overlap and must be encompassed by a power of 2. So 100 hosts can only be satisfied by 128 or 2^7, or a /25. That means the network

is 200.16.27.0/25 (if we say we want big blocks low) meaning ips 200.15.27.0-128 (similar to above).

Its easier to visualize than to calculate, but it is all digital math that drives the rules.

Use this to check, but understand it:

- Crim LiarLv 78 months ago
So, how does the existing netmask work? when you've figured that out, all you have to do is figure out how to further refine this for your subnets!