What is Variable Length Subnet Masking (VLSM)?

VLSM allows using different subnet mask lengths within the same network, enabling more efficient IP address allocation by creating subnets of various sizes based on requirements.

Python:

import ipaddress

def calculate_subnet(ip_with_prefix):
    network = ipaddress.IPv4Network(ip_with_prefix, strict=False)
    
    return {
        'network_address': str(network.network_address),
        'broadcast_address': str(network.broadcast_address),
        'subnet_mask': str(network.netmask),
        'prefix_length': network.prefixlen,
        'num_hosts': network.num_addresses - 2,
        'host_range': f"{network.network_address + 1} - {network.broadcast_address - 1}"
    }

# Example usage
result = calculate_subnet("192.168.1.100/24")
print(f"Network: {result['network_address']}")
print(f"Broadcast: {result['broadcast_address']}")
print(f"Hosts: {result['num_hosts']}")
            

JavaScript:

function calculateSubnet(ip, prefixLength) {
    const ipNum = ipToNumber(ip);
    const mask = (0xFFFFFFFF << (32 - prefixLength)) >>> 0;
    
    const networkAddr = ipNum & mask;
    const broadcastAddr = networkAddr | (0xFFFFFFFF >>> prefixLength);
    const numHosts = Math.pow(2, 32 - prefixLength) - 2;
    
    return {
        networkAddress: numberToIp(networkAddr),
        broadcastAddress: numberToIp(broadcastAddr),
        subnetMask: numberToIp(mask),
        numHosts: numHosts,
        firstHost: numberToIp(networkAddr + 1),
        lastHost: numberToIp(broadcastAddr - 1)
    };
}

function ipToNumber(ip) {
    return ip.split('.').reduce((acc, octet) => (acc << 8) + parseInt(octet), 0) >>> 0;
}

function numberToIp(num) {
    return [(num >>> 24) & 255, (num >>> 16) & 255, (num >>> 8) & 255, num & 255].join('.');
}