IPv4 Range to CIDR Calculator

Why Arbitrary IP Ranges Often Require Multiple CIDR Blocks

A single CIDR block of prefix length /N must obey two strict binary constraints: its size must be an exact power of two (2^(32−N)), and its starting 32-bit integer address must be evenly divisible by that block size (meaning the trailing 32 − N bits of the start address are all zeros).

When an IP allocation or firewall rule starts or ends on an unaligned boundary—for example, 192.168.1.1 through 192.168.1.6—no single CIDR prefix can cover those 6 addresses without spilling over into .0 or .7. Our algorithm steps through the range using 64-bit BigInt bitmask alignment, greedily selecting the largest aligned power-of-two block at each step until the entire range is covered. Compare individual blocks with our IPv4 Subnet Calculator.