IPサブネット計算機 - IPv4・IPv6 CIDR計算機 オンライン

// IP Subnet Calculator in JavaScript

function ipv4ToInt(ip) {
  const parts = ip.split('.').map(Number);
  return ((parts[0] << 24) | (parts[1] << 16) | (parts[2] << 8) | parts[3]) >>> 0;
}

function intToIpv4(num) {
  return [
    (num >>> 24) & 0xFF,
    (num >>> 16) & 0xFF,
    (num >>> 8) & 0xFF,
    num & 0xFF,
  ].join('.');
}

function calculateSubnet(ip, cidr) {
  const ipInt = ipv4ToInt(ip);
  const mask = cidr === 0 ? 0 : (~0 << (32 - cidr)) >>> 0;
  const wildcard = (~mask) >>> 0;
  const network = (ipInt & mask) >>> 0;
  const broadcast = (network | wildcard) >>> 0;
  const totalAddresses = Math.pow(2, 32 - cidr);
  const usableHosts = cidr >= 31 ? (cidr === 32 ? 1 : 2) : totalAddresses - 2;

  return {
    networkAddress: intToIpv4(network),
    broadcastAddress: intToIpv4(broadcast),
    subnetMask: intToIpv4(mask),
    wildcardMask: intToIpv4(wildcard),
    firstUsable: intToIpv4(cidr >= 31 ? network : network + 1),
    lastUsable: intToIpv4(cidr >= 31 ? broadcast : broadcast - 1),
    totalAddresses,
    usableHosts,
  };
}

// Example
const result = calculateSubnet('192.168.1.100', 24);
console.log('Network:', result.networkAddress);    // 192.168.1.0
console.log('Broadcast:', result.broadcastAddress); // 192.168.1.255
console.log('Mask:', result.subnetMask);            // 255.255.255.0
console.log('Hosts:', result.usableHosts);          // 254