IP Range / CIDR Converter
Convert a start/end IP pair to CIDR notation, or expand a CIDR to its IP range.
About IP Range
Takes a start and end IP address and converts that range into the smallest set of CIDR blocks that exactly cover it. This comes up whenever you have an IP range from a source that doesn't speak CIDR — a firewall vendor's allow-list, a cloud provider's published range — and need to translate it into notation your router or firewall actually accepts. Ranges that don't align to a clean power-of-two boundary get broken into multiple CIDR blocks automatically rather than requiring manual binary math.
A range that doesn't start on a clean power-of-two boundary can expand into a surprising number of small CIDR blocks rather than one tidy one — if a firewall has a hard limit on allow-list entries, it's worth re-requesting the range from its source with cleaner boundaries.