So, let's say that you are a new Linux admin (or you just want to block hacking attacks on your desktop).
And you just have found a contiguous range of ip addresses that are hitting your server; all trying the standard bevy of hacks and attacks on your website...
...and you would just like to block the whole range.
It is sometimes a pain to remember the right CIDR netmask numbers to add after the starting ip address to block a range.
Fortunately neustar has a nice tool to help with this calculation.
Just type in the starting ip (in our example, "22.214.171.124"), followed by anything from /32 to /1, to see what all would be blocked by your chosen range.
You may notice that whole 1, 2, 4, 8 doubling-thing that is going on there. Each lower number doubles the amount of ips that would be blocked by the prior number.
/24 is commonly used, as it blocks the lower 256 ip numbers; so 126.96.36.199/24 would block the ip range 188.8.131.52 to 184.108.40.206.
Tip: You don't want to use /1, as that can be a very wide range of ips. For example, 220.127.116.11/1 would block 2,147,483,648 ips, or about ½ of the IPv4 internet.
Note: The IP used is from Debian.
Don't block Debian :)