Subnet / CIDR Calculator

How it works

A CIDR prefix /n keeps the first n bits as the network:

network   = address AND mask
broadcast = network OR NOT mask
hosts     = 2^(32 − n) − 2

The two reserved addresses (network and broadcast) don’t apply to /31 point-to-point links (RFC 3021) or /32 single hosts. The wildcard mask is the inverse, as used in Cisco ACLs and OSPF.

Split divides the network into equal subnets with a longer prefix: a /24 gives 4 × /26 of 62 hosts each.

IPv6

IPv6 addresses are 128 bits. The tool expands and compresses them in the RFC 5952 canonical form (lowercase, no leading zeros, the longest run of zero groups as ::). Ordinary LANs are always /64.

References

• RFC 4632 — CIDR
• RFC 5952 — IPv6 text representation