CIDR controls the network boundary
The prefix length states how many leading bits identify the network. A /24 has 24 network bits and eight host bits, so each block contains 256 addresses. The input address may be any address inside the block; the calculator clears host bits to obtain the network address and sets them to obtain the broadcast address.
Subnet and wildcard masks are complements
A subnet mask contains one bits for the prefix followed by zero bits. Its wildcard mask reverses every bit. For /24, the subnet mask is 255.255.255.0 and the wildcard mask is 0.0.0.255. Wildcard masks are used by some access-control and routing syntaxes, but their interpretation depends on the platform.
Usable hosts depend on subnet purpose
For traditional prefixes from /0 through /30, this calculator excludes the network and broadcast addresses from the conventional usable-host range. Under RFC 3021, a /31 can use both addresses on a point-to-point link and has no distinct broadcast address. A /32 represents one host route. Some systems and network roles apply different rules.
Address scope is not reachability
The scope note recognizes common ranges such as RFC 1918 private space, loopback, link-local, carrier-grade NAT, documentation, multicast, benchmarking, and reserved space. It classifies the entered address only. Routing, firewall policy, NAT, VPNs, interfaces, and cloud configuration determine actual reachability.
No DNS or network request is performed
The arithmetic runs entirely in this browser tab. The tool does not look up the address, test connectivity, scan hosts, query DNS, or upload the value. Decimal octets with leading zeroes are rejected to avoid software-dependent octal interpretations.
Confirm subnet intent before changing routers, firewalls, DHCP pools, ACLs, VPNs, or cloud networks. This calculator covers IPv4 CIDR arithmetic only; it does not validate an organization’s address allocation, detect overlap across other networks, calculate IPv6, or guarantee vendor-specific configuration syntax.