CIDR Merger
Merge a list of IPv4 addresses and CIDR blocks into the fewest blocks: duplicates removed, overlaps and adjacent ranges joined.
Free · No sign-up · Your inputs stay in your browser
Input
Merge and deduplicate CIDR ranges
Output
Aggregated
7 entries became 3, covering 1,049,602 addresses
Overlapping and adjacent blocks are joined and then re-cut into the fewest valid CIDR blocks, so the result covers exactly the same addresses. Useful before pasting a provider's published ranges into a security group, which counts every rule against its limit. IPv4 only.
Runs in this browser. Nothing you paste is sent to a server.
About this tool
Method, assumptions, practical next steps, and limits.
Where long lists come from
Allow lists grow by accretion: office ranges, VPN pools, a CDN's published ranges, partner IPs. Many entries end up contained in others or adjacent to each other. Security groups, WAF rules and Nginx configs all get shorter and easier to audit after aggregation, and cloud providers cap the number of rules per group.
Same coverage, guaranteed
Aggregation never widens a list: two /25s become a /24 only when together they are exactly that /24. Single addresses are treated as /32 blocks.