Whereas classful network design for ipv4 sized the network prefix as one or more 8-bit groups, resulting in the blocks of class a, b, or c addresses, classless inter-domain routing allocates address space to internet service providers and end users on any address bit boundary. I saw frm the book stated classful routing protocol doesn't support vlsm but a later example it uses vlsm model with the following classful address in the figure aren't those classful addresses then why appeared in vlsm model.
I do not think that anyone does real classful routing with fixed length subnet masking other than people experimenting in a lab while they learn the fundamentals of networking as far as the relationship between vlsm and classless routing i would say that they developed at the same time.
A classful routing protocol will not send the subnet mask along with the routing update so this is what will happen: r1 and r3 don’t send the subnet mask along with the routing update so it will advertise the classful network which is 1721600 in this case. Classful vs classless routing june 1, 2011 may 5, 2011 ryan before the internet and general networking become popular into what it is now, there were and still are routing protocols that only do classful routing.
Classful and classless routing is defined as if particular ip address ex19216811/24 this is defined as classfull routing and 19216811 without specific subnetting is defined as classless routingin 19216811/24 loopbacks can be created with defined subnett mask like 255255255224. A classful network is a network addressing architecture used in the internet from 1981 until the introduction of classless inter-domain routing in 1993 the method divides the ip address space for internet protocol version 4 (ipv4).
Classful vs classless routing protocols (continued) classless routing protocols do send the subnet mask with their updates thus, variable length subnet masks (vlsms) are allowed when using classless routing protocols examples of classful routing protocols include ripv1 and igrp.