How to determine IP range given Subnet mask


Question:
Given a computer has an IP address of 192.168.1.101 and a subnet mask of 255.255.255.240 how do I find the range of IP addresses on this subnet?

Answer:
In the subnet mask, find the first octet that is not a 255. In your example, its the 4th octet, and its 240. So take 256 and subtract 240, which gives us 16. So you now know that these networks, the 192.168.1.x networks, all have a range of 16. So just start listing them…

192.168.1.0
192.168.1.16
192.168.1.32
….48
….64
….80
….96
….112

Here we can stop. Your address, 192.168.1.101 falls into the .96 network. .96 encompasses all ip addresses from 192.168.1.96 to 192.168.1.111, because we know that 192.168.1.112 starts the next network.
Related
Understanding the /24 after the IP
Subnet Table

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