bit field Number
bit field Number of networks Addresses per network Start address End address A 0 8 24 128 (27) 16,777,216 (224) 0.0.0.0 127.255.255.255 B 10 16 16 16,384 (214) 65,536 (216) 184.108.40.206 220.127.116.11 C 110 24 8 2,097,152 (221) 256 (28) 192.0.0.0 18.104.22.168 Classful network design served its purpose in the startup stage of the Internet, but it lacked scalability in the face of the rapid expansion of the network in the 1990s. The class system of the address space was replaced with
Classless Inter-Domain Routing
Classless Inter-Domain Routing (CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes. Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.