Subnet Mask Calculator

1. Input parsing

• The tool accepts either a single value with CIDR (for example 192.168.1.10/24) or two fields: an IPv4 address and a mask (dotted mask like 255.255.255.0, numeric 24, or /24 form). The parser first normalizes these inputs and validates the IPv4 dotted-quad format.

2. Mask validation and conversion

• If a dotted mask is provided it is converted to a 32-bit mask number and validated for contiguous '1' bits (non-contiguous masks are rejected). Numeric CIDR prefixes are validated to be integers between 0 and 32. The tool converts between CIDR, dotted decimal mask, wildcard mask, and a grouped binary representation for clarity.

3. Core network calculations

• The core math uses bitwise operations on 32-bit unsigned representations of IPv4 addresses:
• Network address = IP & mask
• Broadcast address = network | (~mask)
• Total hosts = 2^(32 - prefix)
• Usable hosts = total - 2 for common subnets (with explicit handling for /31 and /32)
• First and last usable host addresses are computed with attention to edge cases so the result matches common network planning conventions.

4. Reverse subnetting (CIDR suggestion)

• When you enter a desired usable-host count, the tool finds the most specific prefix whose usable-host count meets or exceeds your request. It applies that prefix to the mask field.

5. UX and output

• All logic is pure and client-side for instant feedback. The UI shows structured results (Network/CIDR, Broadcast, Mask, Wildcard, Binary mask, host range, counts) and provides copy buttons, a CodeEditor for binary mask, and quick action presets for common masks. Validation errors are shown as clear, human-readable alerts.

Notes on special cases

• /31: treated as a two-address point-to-point block; the tool shows both addresses and explains their behavior.
• /32: single IP host route; total and usable hosts are shown accordingly.