Visualize CIDR blocks, calculate IP ranges, and check if addresses fall within subnets. Supports IPv4 and IPv6.
A CIDR prefix such as 192.168.1.64/26 describes an aligned address block, not merely an address followed by a size. Enter an IPv4 or IPv6 prefix to see the block's first and last addresses and its address count, then test whether another address falls inside it. The common surprise is that the range covers every address selected by the prefix bits. For IPv4, this includes addresses commonly designated as the network and broadcast addresses, so the total should not automatically be treated as a usable-host count.
A concrete input and expected output from the current implementation.
Input
CIDR: 192.168.1.64/26 Address to check: 192.168.1.100
Expected output
Range: 192.168.1.64 to 192.168.1.127 Total addresses: 64 192.168.1.100 is within 192.168.1.64/26
A /26 prefix leaves 6 variable bits, giving 2^6, or 64, addresses. The resulting last-octet range is 64 through 127, which includes 100.
The number after the slash is the count of fixed leading bits. The remaining bits can vary: setting them all to zero gives the first address, while setting them all to one gives the last. IPv4 addresses contain 32 bits and IPv6 addresses contain 128 bits, so the same prefix length can represent very different block sizes.
An address belongs to a CIDR block when its fixed leading bits match the block's prefix. The address and block must use the same IP version; an IPv4 address cannot belong directly to an IPv6 block. Different valid IPv6 spellings, including compressed zero runs and uppercase hexadecimal digits, can represent the same numeric address.
A /26 divides the final IPv4 octet into blocks beginning at 0, 64, 128, and 192. The value 70 falls in the 64 through 127 block. Its host bits do not shift the prefix boundary, so the enclosing network begins at 192.168.1.64.
No. The result only shows that the numeric address shares the required prefix bits. It says nothing about routing, firewall policy, interface assignment, NAT, availability, or whether a private or special-use address is appropriate for the intended deployment. Those conditions must be checked separately on the relevant network.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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