Enter an IP address and CIDR prefix to see network address, broadcast address, host range, subnet mask, and total hosts.
A subnet divides a larger network into smaller segments. The CIDR notation (like /24) indicates how many bits of the 32-bit IPv4 address are used for the network portion. The remaining bits define the host range within that network.
Example: 192.168.1.100/24 means the first 24 bits are the network (192.168.1.0), leaving 8 bits for hosts (256 addresses, 254 usable).
IP subnetting is the practice of dividing a single network into smaller, more manageable sub-networks (subnets). Every device on the internet has an IP address -- a 32-bit number written as four decimal octets separated by dots (like 192.168.1.100). The subnet mask determines which portion of the address identifies the network and which identifies the individual host (device) on that network. This division is essential for routing traffic efficiently, improving security through network segmentation, and conserving IP address space.
CIDR (Classless Inter-Domain Routing) notation simplifies subnet representation by appending a slash and number to the IP address. The number after the slash indicates how many of the 32 bits belong to the network portion. A /24 subnet uses 24 bits for the network and 8 bits for hosts, giving 256 total addresses (2^8) with 254 usable host addresses (the first is the network address and the last is the broadcast address). A /16 subnet uses 16 bits for the network and 16 for hosts, allowing 65,534 usable addresses.
Network administrators use subnetting daily to design network architectures, configure routers and firewalls, troubleshoot connectivity issues, and plan IP address allocation. A company might use a /24 subnet for each department (giving up to 254 devices per department), with a /16 or larger supernet encompassing the entire organization. Understanding subnetting is a fundamental skill for network engineers, system administrators, and cybersecurity professionals.
| CIDR | Subnet Mask | Total IPs | Usable Hosts |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 |
| /30 | 255.255.255.252 | 4 | 2 |
| /24 | 255.255.255.0 | 256 | 254 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
A /24 subnet has a mask of 255.255.255.0, providing 256 IP addresses (254 usable for hosts). It is the most common subnet size for small networks and corresponds to the old "Class C" network.
CIDR (Classless Inter-Domain Routing) notation writes an IP address followed by a slash and the number of network bits. For example, 10.0.0.0/8 means the first 8 bits are the network portion.
The first address in a subnet is the network address (identifies the subnet itself) and the last is the broadcast address (used to send messages to all hosts). Neither can be assigned to a device, so usable hosts = total - 2.