The document discusses classful and classless IP addressing. Classful addressing used the first octet to determine the network portion, but IP addresses were depleting rapidly. To conserve addresses, CIDR was introduced using VLSM to allow variable length subnet masks and more efficient use of addresses. CIDR and VLSM allow networks to be further subnetted as needed and routes to be summarized, making more efficient use of the available IPv4 address space.