IPv4 Range Expander
How to use this IPv4 range expander
- Type a start and end IP address defining your range.
- The tool calculates the minimal set of CIDR blocks that exactly cover that range.
- Use the result in firewall rules or routing configuration.
Why does a range need multiple CIDR blocks?
CIDR blocks must start on an address boundary aligned to their size (a /24 must start at a multiple of 256, for example). Arbitrary ranges rarely align perfectly, so they're split into the largest possible aligned blocks that fit.
Why do I sometimes get many small CIDR blocks instead of one?
This happens when the range doesn't align to a clean power-of-2 boundary — the algorithm has to break it into the fewest aligned blocks possible, which can still be several for odd ranges.
Can I use this for firewall rules directly?
Yes, most firewalls and cloud security groups (AWS, Cloudflare, etc.) accept CIDR notation directly, so you can paste the generated blocks as-is.