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IPv4 CIDR Calculator CLI

A Node CLI that parses an IPv4 CIDR block and prints the network address, broadcast address, netmask, and the range of usable host addresses.

node --version

node cidr.mjs 192.168.1.10/24

node --test cidr.test.mjs

Prints the network, broadcast, netmask, and host range for the given CIDR block.

What it does

Computes the addresses that matter inside an IPv4 CIDR block using integer math on the 32-bit address value.

function parseCidr(input) {
  const [ip, prefixRaw] = input.split('/');
  const prefix = Number(prefixRaw);
  const parts = ip.split('.').map(Number);
  if (parts.length !== 4 || parts.some((n) => n < 0 || n > 255) || !Number.isInteger(prefix) || prefix < 0 || prefix > 32) {
    throw new Error('invalid cidr: ' + input);
  }
  const value = ((parts[0] << 24) | (parts[1] << 16) | (parts[2] << 8) | parts[3]) >>> 0;
  return { value, prefix };
}

function toIp(value) {
  return [24, 16, 8, 0].map((shift) => (value >>> shift) & 255).join('.');
}

const { value, prefix } = parseCidr(process.argv[2] ?? '');
const mask = prefix === 0 ? 0 : (0xffffffff << (32 - prefix)) >>> 0;
const network = (value & mask) >>> 0;
const broadcast = (network | (~mask >>> 0)) >>> 0;
const hosts = Math.max(0, broadcast - network - 1);
console.log('network  ' + toIp(network));
console.log('broadcast ' + toIp(broadcast));
console.log('netmask  ' + toIp(mask));
console.log('hosts    ' + (hosts ? toIp(network + 1) + ' - ' + toIp(broadcast - 1) : 'none'));

It rejects prefixes outside 0 to 32 and reports a /31 and /32 as having no usable host range, which matches how those blocks actually behave.

Run and verify

node cidr.mjs 192.168.1.10/24

Run with any host address inside a block; the calculator normalises it to the containing network.

Expected Output

For 192.168.1.10/24 the program should print the network, broadcast, netmask, and host range. The output is:

network  192.168.1.0
broadcast 192.168.1.255
netmask  255.255.255.0
hosts    192.168.1.1 - 192.168.1.254

A /31 or /32 block prints none as the host range, and an invalid prefix exits with an error instead of computing garbage.

Limitations

IPv4 only; IPv6 needs 128-bit handling. Usable-host rules for /31 and /32 follow the common convention and may differ from some vendor documentation.