The Wikipedia link is here Classless Inter-domain Routing
And here is the basic information you need to know.
A CIDR identifies a machine connected to a network.
An example CIDR for IPV4 address looks like this
14 are four octets. An octet represents
8 bits. We use four octets, so we are using
32 bits to represent the machine.
A bit can have two possibilities either
1. So, an octet can have 256 (2 ** 8) values, starting from 0 and ending with 255, which means 4 octets can represent 4,294,967,296 possibilities (2 ** 32).
But, the number after the
/ puts a limit on this.
Before, I explain how the limit is applied, I'll have to explain what number
24 means. The number
24 could also have been represented as 4 octets. If we did, it would look like
255.255.255.0. The number
24 is a compact way of representing these 4 octets. Are you wondering how these are equivalent? The value
255 when represented by a an octet (8 bits) looks like this
255.255.255.0 would be
11111111.11111111.11111111.00000000. I put
. in between for readability. As you can see, this big number has
24 leading bits set to
1. That's the link between the two representations.
This number is telling us that while using the address
192.168.100.14, don't use the first 24 bits or the first 3 octets. That is,
192.168.100 are off limits. That leaves us with only the last octet, so only 256 possible values :( ! Imagine if this number was
31, that leaves only
1 bit or two possibilities.
The 3 octets that we do not use, along with a a
0 for the fourth octet
192.168.100.0 represents something called a
routing prefix. If you represent this routing prefix in the form
255.255.255.0, it's called the
subnet mask and logically represents the same thing.