Calculate subnets and address ranges
Divide a network into subnets using CIDR notation. Calculate network address, broadcast, host range, and available host count.
- 1
A subnet is defined by an IP address and a prefix length (CIDR, e.g., 192.168.1.0/24). The prefix determines the network/host boundary: /24 means the first 24 bits are the network, last 8 are hosts. The network address has all host bits as 0; the broadcast has all host bits as 1; usable hosts are in between.
- 2 IP Address Info →
Enter an IP address with CIDR prefix (e.g., 192.168.1.0/24) to see the network address, broadcast address, host range, and number of usable hosts. This is essential for network planning and firewall configuration.
- 3 Precision Calculator →
Calculate the number of usable hosts: 2^(32-prefix) - 2 (subtract network and broadcast). For /24: 2^8 - 2 = 254 hosts. For /30: 2^2 - 2 = 2 hosts (point-to-point link). For /31: 2 hosts (RFC 3021, no broadcast).
Frequently asked questions
- What is CIDR notation?
- Classless Inter-Domain Routing notation: IP/prefix, e.g., 192.168.1.0/24. The prefix (0-32 for IPv4, 0-128 for IPv6) specifies the number of network bits. It replaced the classful system (A, B, C) which wasted addresses by fixing the network/host boundary.
- Why subtract 2 from the host count?
- The first address (all host bits 0) is the network address, and the last (all host bits 1) is the broadcast address. Neither can be assigned to a host. For a /24: 256 - 2 = 254 usable hosts. /31 (RFC 3021) and /32 are exceptions.
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