Plan an IPv4 network before assigning addresses
Subnetting divides an IPv4 address space into networks of a chosen size. Enter an address and a CIDR prefix to see the network address, subnet mask, broadcast address, and host range. These values help you configure router interfaces, DHCP scopes, firewall rules, and static routes without placing devices in the wrong network.
For example, 192.168.16.21/24 belongs to 192.168.16.0/24. The subnet contains 256 addresses, from 192.168.16.0 to 192.168.16.255. In a conventional subnet, the first address identifies the network and the last is the broadcast address; 254 addresses remain for hosts. A smaller prefix number means a larger address block.
Choosing a prefix
A /24 uses the mask 255.255.255.0. A /26 divides the same /24 address block into four networks of 64 addresses each, normally with 62 usable host addresses. Pick a prefix that leaves room for the devices you expect, then check that neighboring subnets do not overlap. The wildcard mask shown in the results is the bitwise inverse of the subnet mask and is useful in some access control lists.
Special cases and practical checks
The calculator treats /31 as a point-to-point link with two usable endpoint addresses and /32 as a single host route. These cases have no separate conventional network and broadcast reservations. For ordinary networks from /0 through /30, the usable range excludes the network and broadcast addresses. Before applying a plan, confirm the gateway address, VLAN, DHCP reservations, and routing configuration on your actual equipment.