Why Arbitrary IP Ranges Require Multiple CIDR Blocks
In IPv4 routing, a single CIDR block must satisfy two strict binary rules:
- The size of the block must be an exact power of two (1, 2, 4, 8, 16, 32, 64, 128, 256, etc.).
- The starting IP must be an exact integer multiple of the block size.
If your range begins at an arbitrary host number (e.g. .10 to .100), no single subnet mask can represent it. Instead, network firewalls and route filters use a greedy CIDR decomposition algorithm to break the range into the smallest possible number of clean prefix blocks.