Find out the active local IP

Question

I need to find out the local Ip address, for that reason I was using the following code:

IPHostEntry host;
string localIP = "";
host = Dns.GetHostEntry(Dns.GetHostName());
foreach (IPAddress ip in host.AddressList)
{
    if (ip.AddressFamily == AddressFamily.InterNetwork)
    {
        localIP = ip.ToString();
        break;
    }
}
return localIP;

I find out that when a PC has more than one IP with AddressFamily.InterNetwork I get always the first one. However I can't find any property to find out the active IP.

How can I get the correct IP?

Thanks for any tip!

Answer 1

Bwall has a fitting solution posted in this thread.

foreach(NetworkInterface ni in NetworkInterface.GetAllNetworkInterfaces())
{
   if(ni.NetworkInterfaceType == NetworkInterfaceType.Wireless80211 || ni.NetworkInterfaceType == NetworkInterfaceType.Ethernet)
   {
       Console.WriteLine(ni.Name);
       foreach (UnicastIPAddressInformation ip in ni.GetIPProperties().UnicastAddresses)
       {
           if (ip.Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
           {
               Console.WriteLine(ip.Address.ToString());
           }
       }
   }  
}

The important thing in this piece of code is, that it only lists IP addresses of ethernet and wireless interfaces. I doubt you'll have a serial connection active, so this won't matter most likely. Alternativly you can always edit the if statement.

//EDIT If you only want to IP address which actually connects to the internet use Hosam Aly's solution

This is his code:

static IPAddress getInternetIPAddress()
{
    try
    {
        IPAddress[] addresses = Dns.GetHostAddresses(Dns.GetHostName());
        IPAddress gateway = IPAddress.Parse(getInternetGateway());
        return findMatch(addresses, gateway);
    }
    catch (FormatException e) { return null; }
}

static string getInternetGateway()
{
    using (Process tracert = new Process())
    {
        ProcessStartInfo startInfo = tracert.StartInfo;
        startInfo.FileName = "tracert.exe";
        startInfo.Arguments = "-h 1 www.example.com
        startInfo.UseShellExecute = false;
        startInfo.RedirectStandardOutput = true;
        tracert.Start();

        using (StreamReader reader = tracert.StandardOutput)
        {
            string line = "";
            for (int i = 0; i < 5; ++i)
                line = reader.ReadLine();
            line = line.Trim();
            return line.Substring(line.LastIndexOf(' ') + 1);
        }
    }
}

static IPAddress findMatch(IPAddress[] addresses, IPAddress gateway)
{
    byte[] gatewayBytes = gateway.GetAddressBytes();
    foreach (IPAddress ip in addresses)
    {
        byte[] ipBytes = ip.GetAddressBytes();
        if (ipBytes[0] == gatewayBytes[0]
            && ipBytes[1] == gatewayBytes[1]
            && ipBytes[2] == gatewayBytes[2])
        {
            return ip;
        }
    }
    return null;
}

What it basically does, is trace the route to www.example.com and processes the right IP from there. I tested the code on my machine and needed to change the iterations from 9 to 5 to get the right line from stream. You better recheck it or you might into a NullReferenceException because line will be null.

Answer 2

I have picked this up from internet a while ago.

        string strHostName = System.Net.Dns.GetHostName(); ;
        IPHostEntry ipEntry = System.Net.Dns.GetHostEntry(strHostName);
        IPAddress[] addr = ipEntry.AddressList;

This should give you an array of all the ip addresses of your pc.

Answer 3

    static string GetActiveIP()
            {
                string ip = "";
                foreach (NetworkInterface f in NetworkInterface.GetAllNetworkInterfaces())
                {
                    if (f.OperationalStatus == OperationalStatus.Up)
                    {
                        IPInterfaceProperties ipInterface = f.GetIPProperties();
                        if (ipInterface.GatewayAddresses.Count > 0)
                        {`enter code here`
                            foreach (UnicastIPAddressInformation unicastAddress in ipInterface.UnicastAddresses)
                            {
                                if ((unicastAddress.Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork) && (unicastAddress.IPv4Mask.ToString() != "0.0.0.0"))
                                {
                                    ip = unicastAddress.Address.ToString();
break;

                                }                          
                            }`enter code here`
                        }


                    }
                }
                return ip;
            }