Subnet / CIDR

Enter an IPv4/IPv6 CIDR and Calculate (Enter also works). Edits then update after 150 ms without typing. Examples calculate directly and set a matching target prefix: IPv4, IPv6, /31 endpoints or /32 addresses. Clear empties the CIDR and stops live updates. Host bits are cleared for the network; 192.168.1.7/24 becomes 192.168.1.0/24 with 254 ordinary usable hosts. Details shows broadcast/wildcard/reverse zone where applicable. No network query or configuration change. Copy network copies the normalized CIDR without the host bits.

IPv4 prefixes /0–/30 use the ordinary subnet convention excluding network and directed broadcast. A /31 offers two endpoint addresses on point-to-point links (RFC 3021), with no directed broadcast; /32 is a single host route. IPv6 counts every address in the mathematical block and has no broadcast. Address counts do not establish real-world assignability, available leases or reachability. Arithmetic uses exact integers, including 2^128 for ::/0.

Open Subnets to see the split immediately, then edit the target prefix or press Enter. The target must be at least the parent prefix and at most 32/128. /24 to /26 gives four contiguous blocks of 64 addresses. IPv4 rows show usable host ranges or both /31 endpoints; single-address blocks need only CIDR. IPv6 rows show the last address, not assignability. At most the first 1,024 blocks appear; an explicit warning marks partial lists. Copy beside the prefix copies only those listed CIDRs, one per line. Long lists scroll locally; edited inputs immediately invalidate old rows/copy feedback.

IPv4 octets use decimal without leading zeros. IPv6 accepts compressed, full and IPv4-embedded forms; :: must replace at least one group. No zone IDs, bracketed URLs or dotted netmasks. The network calculation accepts up to 256 CIDR characters. Reverse zones are shown only at IPv4 octet (/8) or IPv6 nibble (/4) boundaries; other prefixes require additional delegation arrangements, not a made-up host PTR. No supernet aggregation or public/private/routing classification. Conventions: RFC 4291, RFC 3021, RFC 2317 and RFC 3596.

Only raw CIDR, target-prefix draft and open-section preferences are remembered. Reloading/changing language/reopening restores no calculation, field error or scroll position. Old evaluated/parent/view flags are ignored. A new CIDR keeps your target draft and validates it against the new bounds; choose an example to explicitly set a matching pair. Invalid and overlong inputs stay editable. Beyond 100000 serialized characters the complete TXT download and live app retain the draft, while the previous saved inputs stay protected. The 256-character network calculation limit does not truncate the original. No session files or computed histories.