Use CIDR Toolkit for firewall rules, cloud security groups, VPN routes, proxy allowlists, and IP access reviews. It calculates exact IPv4 ranges, merges overlapping blocks, subtracts excluded networks, and catches accidental overlap before a rule reaches production.
This is intentionally more than a subnet calculator: paste real allowlists, remove a partner range, collapse redundant entries, or compare two lists from different systems without exposing private infrastructure data.
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