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I know how to do the classic "network addressing" when I am allowed to waste IP addresses. For example, if I need to hook up 9 computers, I could use a /28 subnet, which allows 16 hosts to be mapped within it see the Wikipedia article on CIDR for details.
But what if I am asked to minimize the number of wasted IP addresses?
For example in this case:
Imagine, there is a network 6 which has 8 computers. We see that if the IP address wasting was not allowed, then the network 6 would use the unused range: 12.0.2.128 - 12.0.2.255
So, the network 6 would look like this:
- network address: 12.0.2.128
- subnet mask: 28
- 1st address of network: 12.0.2.129
- last address of network: 12.0.2.142
- broadcast: 12.0.2.143
What if there is additional network 7 with only 10 computers?
Am I limited to only one CIDR subnet / network for each free unused range, or am I allowed to "put" as many different subnets as can possibly fit within the free unused address range?
You need seven bits (which provide 128 values) to handle 78 nodes (64 <= 78 <= 128). /25 gives you 7 bits for hosts (32 - 25 = 7). The subnet mask doesn't split on anything more granular than even powers of 2. It's the best you can do, and you always want room for expansion anyway. – LawrenceC – 2013-08-05T17:48:29.930