Difference between classful and classless IP (Internet Protocol) Addressing

Currently, I am enrolled in a  CCNA (Cisco Certified Network Associate) Certification Training Course  here in Cebu City, in preparation of course for the CCNA Exam. One major topic discussed here is the IP (Internet Protocol) addressing, an interesting topic under data communication technology. IP address is assigned to a specified client (device) in a network for its identity and is presented in 32-bit (IPv4) with 4 octets separated by a period, for example: 10111001.00010010.11110001.10100011 or represented as 185.18.241.163 in decimal.

So, when discussing about this certain topic, you will encounter the words Classful & Classless IP addressing. What then is the difference between the two?

Classful IP - also known as the conventional IP addressing, is basically IP addresses classified under a Class with a given range and a default mask.

For the range, we have the following table:

Commonly, we only use Class A, B & C since Class D & E are for multicasting and experimental purposes respectively. By the way, notice that 127 is not included in the range because it is assigned for loopback, usually assigned to your localhost or your PC.

For its subnet mask:

So, for example, if you check your IP address using ipconfig, and shows you with IP address 192.168.2.100 and subnet mask of 255.255.255.0 — that means you’re under a Class C network. Click here for online Classful IP Calculator tool if you need help.

Classless IP – as defined by its name, it does not follow any Class as above. When you encounter and IP address with a subnet mask which is not 255.0.0.0 or 255.255.0.0 nor 255.255.255.0 that means that it’s a classless IP.

I am not really an expert on this topic,  but if you need to understand more in details about this, you can check this site.