IP in CIDR Checker - Is an IP Address in a Range? (IPv4 & IPv6)
IP in CIDR Checker
Check IP addresses against CIDR ranges and see how two ranges overlap
Many Against Many
Paste a list of addresses and a list of ranges and see, for each address, which ranges contain it.
Compare Two Ranges
See whether two CIDR blocks are the same, one inside the other, partly overlapping or separate, with the overlapping addresses.
IPv4 and IPv6
Handles both, including compressed IPv6 forms and IPv4-mapped tails. A bare address counts as a /32 or /128.
Full Privacy
Everything is calculated in your browser.
How CIDR Membership Works
A CIDR range like 10.0.0.0/8 means "every address whose first 8 bits match 10.0.0.0". To test an address you compare just those leading bits: 10.200.5.1 is inside 10.0.0.0/8 because its first byte is 10, while 11.0.0.1 is not. The same idea works for IPv6 with 128 bits, so 2001:db8::1 is inside 2001:db8::/32. The tool does this with exact integer arithmetic on the whole address, so it is correct for every prefix length.
Any two valid CIDR blocks are either identical, one inside the other, or completely separate: they can never overlap only in part, because each block is a run of addresses aligned to a power of two. If you enter an address with host bits set, such as 10.1.2.3/8, it is treated as 10.0.0.0/8 and the tool says so, and a bare address is treated as a single-address range.
Key Takeaways
- Exact: Uses BigInt maths, so /0 to /128 all work, and results match the Python ipaddress module.
- Comments allowed: Lines can end with # comments, handy for pasting from a firewall config.
- Related tools: See also the CIDR Aggregator and the Subnet Calculator.