// Convert IPv4 to long
const long = net_utils.ip_to_long('11.22.33.44');  // 185999660

// Convert long to IPv4
const ip = net_utils.long_to_ip(185999660);  // 11.22.33.44

// Convert decimal to hex
const hex = net_utils.dec_to_hex(20111104);  // 132df00

// Convert hex to decimal
const dec = net_utils.hex_to_dec('132df00');  // 20111104

// Is IPv4 address on a local network?
net_utils.is_local_ipv4('127.0.0.200');   // true (localhost)
net_utils.is_local_ipv4('169.254.0.0');   // true (link local)
net_utils.is_local_ipv4('226.0.0.1');     // false

// Is IPv4 address in RFC 1918 reserved private address space?
net_utils.is_private_ipv4('10.0.0.0');       // true
net_utils.is_private_ipv4('192.168.0.0');    // true
net_utils.is_private_ipv4('172.16.0.0');     // true

// Is IPv6 addr on local network?
net_utils.is_local_ipv6('::1');           // true (localhost)
net_utils.is_local_ipv6('fe80::')         // true (link local)
net_utils.is_local_ipv6('fc00::')         // true (unique local)
net_utils.is_local_ipv6('fd00::')         // true (unique local)

// searches for 'ip' as a hash key in the list object or array
// ip can be a host, an IP, or an IPv4 or IPv6 range
net_utils.ip_in_list(object, ip);
net_utils.ip_in_list(array, ip);
net_utils.ip_in_list(tls.no_tls_hosts, '127.0.0.5');

net_utils.get_mx(domain, (err, mxList) => {
    if (err)  // handle any errors
    for (const mx of mxList) {
        // do something with each mx
    }
})