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IP address in dotted decimal notation

CIDR uses binary notation, while the class-based method uses decimal notation.

Using binary notation

Computers use binary notation for internal processing because they communicate using signals that have only two states: on or off. Since the binary system also has only two values, 0 or 1, computers work using binary notation.

Increased range of network sizes

CIDR translates all IP addresses and subnet masks into binary notation.

CIDR splits an IP address into a set of 32 values instead of the four values used by the class-based system. This division allows for a greater number of different network sizes and optimizes the allocation of IP addresses. When using CIDR, not many IP addresses go unused, as organizations can now obtain IP addresses in numbers that much better match the required number of addresses. CIDR does not define a default subnet mask according to the IP address. Instead, each host is configured with a user-defined subnet mask, and the IP address is sent to each router as part of the data packet. The router then uses a subnet mask from its routing table to determine the network identifier of the computer to which the packet must be forwarded.