It has two components:
- The base IP. (XX.XX.XX.XX)
- The subnet mask (/26)
The base IP represents an IP contained in the range, whereas the subnet mask defines how many bits can change in the IP.
The subnet mask can take two forms. Exempli Gratia (e.g.):
- 255.255.255.0 - This is probably less common.
- /24 - More common and easier to read.
The subnet masks basically allows part of the underlying IP to get additional next values from the base IP.
- /32 allows for 1 IP bit to change = 2^0
- /31 allows for 2 IP = 2^1
- /30 allows for 4 IP = 2^2
- /29 allows for 8 IP = 2^3
- /16 allows for 65,536 IP = 2^16
- /0 allows for all IPs = 2^32
Obviously, you don’t need to memorize all that. Just train your brain to subtract from 32 with whatever is after the slash. You get the number of bits that can be changed. Raise it to the power of 2. These many number of IPs belong to the range.