Review an address-list change
Paste the old configuration into List A and the proposed configuration into List B. Added means B − A; removed means A − B. A smaller subnet inside a larger one is compared by its actual addresses, so splitting a block into equivalent CIDRs does not create a change.
Choose the operation you need
Intersection finds common coverage, union combines both lists, and symmetric difference includes addresses that occur in exactly one list. The output normalizes host bits and merges adjacent blocks only when doing so preserves exact coverage. Counts include network and broadcast addresses, not only assignable hosts.
Export a complete result
The preview shows the first 256 CIDRs. Download complete CIDR list includes every result block. The comparison JSON includes all five operations, normalized input coverage and exact IPv4/IPv6 counts as decimal strings. No addresses are queried, uploaded or saved automatically.
For example, compare 10.0.0.0/24 with 10.0.0.128/25: the removed range is 10.0.0.0/25 and no new addresses are added. Use the CIDR calculator for subnet details and splitting, or the IP Number Converter for numeric representations.
Frequently asked questions
How are overlapping CIDRs compared?
The tool compares address coverage rather than lines of text. It merges duplicates and adjacent intervals before calculating differences, intersection or union. Results use a minimal exact CIDR cover.
Are large IPv6 ranges exact?
Yes. Address arithmetic and counts use BigInt. A /0 contains exactly 2^128 IPv6 addresses, and the tool works with intervals without enumerating those addresses.
Can the lists mix IPv4 and IPv6?
Yes. Each family is compared independently. An IPv4-mapped IPv6 address remains an IPv6 address and is not equated with its embedded IPv4 address.
Are empty inputs or single IP addresses allowed?
An empty input is an empty set. A bare IPv4 address is treated as /32 and a bare IPv6 address as /128. Each list supports 256 nonempty entries and 100,000 characters. A # starts a comment.