IP in CIDR Checker
Check IPv4 and IPv6 addresses against multiple CIDR blocks
About this tool
IP in CIDR Checker compares multiple IPv4 and IPv6 addresses with multiple network blocks in one run. Every input is parsed and normalized, then matched against compatible CIDRs. When an address belongs to nested networks, the most specific longest-prefix match is shown first and broader matches are listed separately. This is useful for firewall rule review, allowlist testing, cloud route validation, and incident-response triage. BigInt calculations run locally and no address list is uploaded.
Frequently Asked Questions
Does the checker support IPv6?
Yes. IPv4 and IPv6 addresses and CIDRs can be mixed in the same batch.
What is longest-prefix matching?
When several CIDRs contain an IP, the block with the largest prefix is the narrowest and most specific match.
Can I check many IPs against many networks?
Yes. Put one IP and one CIDR per line; the tool evaluates the complete set.
Are network and broadcast addresses considered inside an IPv4 CIDR?
Yes. Membership is mathematical, so both boundary addresses are inside the block.
Are IPv4-mapped IPv6 addresses accepted?
Yes. Addresses such as ::ffff:192.0.2.1 are parsed as IPv6 values.
Is any IP information sent to a server?
No. Parsing and CIDR comparisons happen locally.
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