CIDR Merge and Exclude

Merge a list of IPv4 and IPv6 prefixes into the fewest CIDR blocks, find overlaps and duplicates, and subtract ranges. Runs in your browser.

Paste a list of IPv4 and IPv6 prefixes (from a firewall, a cloud provider's published ranges or an allow list) to get the shortest list that covers exactly the same addresses: overlapping and adjacent blocks are merged, duplicates dropped, and entries with host bits set are corrected. Add a second list to remove those addresses from the first, for example "all of 10.0.0.0/8 except the VPN pool". Results were checked against Python's ipaddress module.