IP CIDR Calculator

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its network prefix length. For example, 192.168.1.0/24 means the first 24 bits are the network portion, giving 256 total addresses. For IPv6, 2001:db8::/32 means a /32 prefix with 2^96 addresses in the block.

For IPv4, usable hosts = 2^(32-prefix) - 2 (subtract network and broadcast addresses). A /24 gives 254 usable hosts, a /30 gives 2, and a /31 gives 2 (RFC 3021 point-to-point). For /32, it's a single host route. IPv6 subnets don't have a broadcast address.

A wildcard mask is the inverse of the subnet mask. For a /24 subnet (mask 255.255.255.0), the wildcard is 0.0.0.255. Wildcard masks are used in Cisco ACLs and OSPF area configuration where a 1-bit means 'any value' and a 0-bit means 'must match'.

Yes. Enter any valid IPv6 CIDR notation (e.g. 2001:db8::/32 or fe80::/10). The calculator shows the network address, last address in the block, total address count, and binary representation for all 128 bits.

RFC 1918 defines three private ranges: 10.0.0.0/8 (16.7M addresses), 172.16.0.0/12 (1M addresses), and 192.168.0.0/16 (65K addresses). These are not routed on the public internet. IPv6 uses fc00::/7 (ULA) for private addresses.

For IPv4, the binary view shows the 32-bit representation of the network address, subnet mask, and broadcast address split into four octets (e.g. 11000000.10101000.00000001.00000000). This helps visualize exactly which bits are the network vs host portion.