Fetch (Get) all IPAddress of machine connected on LAN Network in ASP.Net

Hi

I wanted to fetch all IP addresses of all devices connected to LAN but below code is fetching only 192.168.1 series ip address only. But in my LAN there are 

• 192.168.4
• 192.168.5
• 192.168.6
• 192.168.7
• 192.168.8

kindly help me. thank you. below is my code.

static string NetworkGateway()
{
    string ip = null;

    foreach (NetworkInterface f in NetworkInterface.GetAllNetworkInterfaces())
    {
        if (f.OperationalStatus == OperationalStatus.Up)
        {
            foreach (GatewayIPAddressInformation d in f.GetIPProperties().GatewayAddresses)
            {
                ip = d.Address.ToString();
            }
        }
    }

    return ip;
}

public void Ping_all()
{
    string gate_ip = NetworkGateway();
    //Extracting and pinging all other ip's.
    string[] array = gate_ip.Split('.');
    for (int i = 2; i <= 255; i++)
    {  
        string ping_var = array[0] + "." + array[1] + "." + array[2] + "." + i;   
        //time in milliseconds           
        Ping(ping_var, 4, 4000);
    }            
}    

public void Ping(string host, int attempts, int timeout)
{
   for (int i = 0; i < attempts; i++)
    {
        new Thread(delegate()
        {
            try
            {
                System.Net.NetworkInformation.Ping ping = new System.Net.NetworkInformation.Ping();
                ping.PingCompleted += new PingCompletedEventHandler(PingCompleted);
                ping.SendAsync(host, timeout, host);
            }
            catch
            {
                // Do nothing and let it try again until the attempts are exausted.
                // Exceptions are thrown for normal ping failurs like address lookup
                // failed.  For this reason we are supressing errors.
            }
        }).Start();
    }
}