Calculate IPv4 subnet information from CIDR notation. Enter an IP address and prefix length to instantly get the network address, broadcast address, usable host range, subnet mask, wildcard mask, and total host count.
CIDR notation represents a network as IP address + prefix length. /24 means 255.255.255.0 netmask giving 254 usable hosts.
A /24 subnet has 256 addresses. Subtract 2 for network and broadcast addresses leaving 254 usable hosts.
CIDR notation specifies the number of bits in the subnet mask. /24 means 24 bits are the network portion (mask 255.255.255.0), leaving 8 bits for hosts — 256 total addresses, 254 usable. /16 gives 65,536 addresses, /32 is a single host. CIDR allows more flexible address allocation than the old Class A/B/C system.
Traditional fixed-length subnet masking requires all subnets to be the same size, wasting IP addresses. VLSM (Variable Length Subnet Masking) allows different subnets to have different sizes, allocating addresses as needed. For example: headquarters with 100 hosts uses /25 (126 usable), a branch with 20 hosts uses /27 (30 usable), a WAN link with 2 hosts uses /30 (2 usable). Modern network design universally uses VLSM.