What are classless routing protocols

More commonly referred to as classless routing behaviour in reference to protocols. examples are ripv2, eigrp, ospf, isis etc. classless routing protocols submit subnet information in the data they send to other routers. therefore, variable subnet masks can be applied other than the default classful subnet mask. i.e, if the first two bits in the first octet are 0 then it is a class A address, and the first octet only, /8 or 255.0.0.0, is the network portion. hence why the private routing address 10.0.0.0 extends all the way to 10.255.255.255. with classless routing behaviour this can be any subnet mask.