CIDR / Subnet Calculator
Calculate network address, broadcast, subnet mask, wildcard, IP range and usable hosts from any CIDR notation. Supports IPv4 subnetting and common network planning.
What is CIDR notation?+
CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network prefix in the format IP/prefix-length. For example, 192.168.1.0/24 means the first 24 bits are the network part, leaving 8 bits for host addresses — giving 256 total addresses (254 usable).
What is the difference between network and broadcast address?+
The network address is the first address in a subnet (all host bits zero) — used to identify the subnet itself. The broadcast address is the last address (all host bits one) — used to send packets to all hosts on the subnet. Neither can be assigned to a device; usable hosts are everything in between.
How many usable hosts does a /24 subnet have?+
A /24 subnet has 256 total addresses (2^8). Subtracting the network address and broadcast address leaves 254 usable host addresses. Common subnets: /30 = 2 hosts, /29 = 6 hosts, /28 = 14 hosts, /27 = 30 hosts, /26 = 62 hosts, /25 = 126 hosts, /24 = 254 hosts.
What is a wildcard mask?+
A wildcard mask is the inverse of a subnet mask — used in access control lists (ACLs) and OSPF configurations. Where a subnet mask has 1s for network bits, a wildcard mask has 0s. For /24 (mask 255.255.255.0) the wildcard is 0.0.0.255.
What is subnetting?+
Subnetting divides a large network into smaller sub-networks. This improves security (containing broadcast traffic), performance and IP address management. A /24 network can be divided into two /25 subnets, four /26 subnets, and so on.