What is the address class system (Class A, B, C) and why is it considered obsolete in modern networking?

• A.The classful system divided IPv4 into fixed blocks by first octet: Class A (0-127, /8 masks, 16M hosts), Class B (128-191, /16, 65K hosts), Class C (192-223, /24, 254 hosts). Obsolete because it caused massive waste: a company needing 500 hosts had to get a /16 (65,534 addresses, 65,034 wasted). CIDR (RFC 1519, 1993) replaced it by allowing any prefix length, enabling address allocation based on actual need (VLSM)
• B.The class system is still actively used by all modern routers; CIDR is an optional feature for backward compatibility
• C.Class A addresses are reserved for military use only; Classes B and C are used by commercial organizations and cannot be subnetted
• D.The class system was replaced by IPv6; IPv4 still uses classful addressing, which is why IPv4 ran out of addresses