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IPv4 range expander

Given a start and an end IPv4 address, this tool calculates a valid IPv4 subnet along with its CIDR notation.

How to Use

  1. Step 1: Enter the start and end IPv4 addresses of the range.
  2. Step 2: The tool calculates the minimal set of CIDR blocks that cover the range.
  3. Step 3: Copy the CIDR list for use in firewall rules or routing tables.

Frequently Asked Questions

What is CIDR aggregation?

CIDR aggregation finds the smallest set of network prefixes that exactly covers a given IP range.

Why might one IP range result in multiple CIDR blocks?

IP ranges that do not align on power-of-2 boundaries require multiple CIDR blocks to represent exactly.

Why do multiple CIDRs sometimes represent one IP range?

CIDR blocks must be power-of-2 in size and aligned to corresponding boundaries. An arbitrary start-to-end IP range (e.g. 10.0.0.5 to 10.0.0.20) cannot be expressed as a single CIDR — it decomposes into multiple non-overlapping blocks. This tool performs that decomposition automatically for firewall rules.

What are the practical uses of IP range expansion in network configuration?

Practical uses of IP range expansion: firewall rules (allow only specific IP ranges); VPN routing tables (specify which traffic goes through the VPN tunnel); Nginx/Apache allow/deny directives; cloud security group rules (AWS Security Groups, Alibaba Cloud); CDN whitelists; database access control. CIDR is the most concise notation — a single IP range may map to multiple CIDR blocks.