What is the difference between classless and classful IP addresses?

I am assuming you have basic network knowledgeIP ranges are classiefied in 3 classes Class A =  IP  1-126,  default mask is 255.0.0.0 (or /8)Class B  =  IP 128-191, default mask is 255.255.0.0 (or /16)Class C  = IP  192 - 223,  default mask is 255.255.255.0 ( or /24)Any IP that uses its defaul mask is classfull, if it is not using its default mask we call it classlesse.g 10.10.10.20/24 is classless because its falling in the class A range and not using its default /8 mask

adresse destinataire unique et aux adresses du groupe de réseau

https://learningnetwork.cisco.com/thread/34420