IP

Background and History of Subnet Masks Subnet masks were officially introduced to the TCP/IP protocol stack through RFC 950 in 1985 as an innovative technology to solve the serious inefficiency problems of the early internet’s classful addressing system. In the early 1980s, the internet used the A, B, C class system. Class A was identified by the first byte (1-126) supporting approximately 16 million hosts, Class B by the second byte (128-191) supporting approximately 65,000 hosts, and Class C by the third byte (192-223) supporting 254 hosts. This rigid structure caused critical problems. Organizations needing 1,000 hosts had to be allocated Class B (65,534) as Class C (254) was insufficient, wasting over 64,000 IP addresses. Conversely, organizations needing only 300 hosts had to be allocated an entire Class C (254), offering no flexibility. Subnet masks emerged to solve this inefficiency by enabling division of one network into multiple small subnetworks (subnets), allowing arbitrary adjustment of boundaries between network and host portions to precisely allocate the required number of hosts, forming the foundation for CIDR (Classless Inter-Domain Routing) introduction in 1993 and becoming a core concept of modern internet address management. ...

Background and History of CIDR CIDR (Classless Inter-Domain Routing) was officially introduced by the IETF in 1993 through RFC 1517, RFC 1518, and RFC 1519 to overcome the serious limitations of the existing class-based IP address allocation method, and later revised as RFC 2050 in 1998 to become the internet routing standard. From the late 1980s, as the internet grew rapidly, the existing classful addressing system faced two serious problems. First, Class C networks (254 hosts) were too small and Class B networks (65,534 hosts) were too large, not matching actual needs and wasting large amounts of IP addresses. Second, internet routing tables exploded, causing overload on router memory and processing performance. CIDR solved these problems by completely removing the class concept and introducing Variable Length Subnet Mask (VLSM) to allow precise adjustment of network sizes as needed, and enabled dramatic reduction in routing table size through route aggregation or supernetting techniques that consolidate multiple small networks into a single routing entry. ...

What is Classful Addressing Classful Addressing is an IP address allocation method officially introduced in 1981 through the IETF’s RFC 791 document alongside the IPv4 protocol. It was designed to efficiently distribute address space and minimize routing tables in the early Internet network. The system divides network sizes into 5 classes (A, B, C, D, E) based on the bit pattern of the first octet (8 bits) of the IP address, providing different sizes of network address space for each class. ...