[SOLVED] How can send a UDP broadcast to any IP address on the network?

Question

Hi. I'm trying to send a UDP broadcast to any machine within my subnet. It works well when I specify the IP address (e.g. 192.168.0.19), but I need it to be generic (192.168.x.x). How can I do that?

I tried IPAddress.Any, but it's not working. I don't even know what the term is called (IP Masking, maybe?).

// Listener Code:

private void StartUdpListener()
{
    var listener = new UdpClient(_listenPort) { EnableBroadcast = true }; // set EnableBroadcast property to true
    //IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);
    IPEndPoint groupEP = new IPEndPoint(IPAddress.Parse("192.168.255.255"), listenPort); // Should it be 192.168.255.255???

    try
    {
        while (true)
        {
            Console.WriteLine("Waiting for broadcast");
            byte[] bytes = listener.Receive(ref groupEP);

            Console.WriteLine($"Received broadcast from {groupEP} :");
            Console.WriteLine($" {Encoding.ASCII.GetString(bytes, 0, bytes.Length)}");
        }
    }
    catch (SocketException e)
    {
        Console.WriteLine(e);
    }
    finally
    {
        listener.Close();
    }
}

 // Server Code:

private void SendUdpBroadcast()
{
    var myIpAddressSegments = MyIpAddress.GetAddressBytes();
    var firstTwoOctetsSegment = string.Join(".", myIpAddressSegments[0], myIpAddressSegments[1]);

    Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

    var broadcast = IPAddress.Parse(firstTwoOctetsSegment + ".255.255"); // Gets set to 192.168.255.255. Is this correct???

    var sendbuf = Encoding.ASCII.GetBytes("Testing...");
    var ep = new IPEndPoint(broadcast, _listenPort);

    s.SendTo(sendbuf, ep);

    Console.WriteLine("Message sent to the broadcast address");
}

Answer 1

Given your gateway and subnet mask the broadcast IP is 192.168.0.255.

Sender

using System;  
using System.Net;  
using System.Net.Sockets;  
using System.Text;  
  
class Program  
{  
    static void Main(string[] args)  
    {  
        Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);  
  
        IPAddress broadcast = IPAddress.Parse("192.168.0.255");  
  
        byte[] sendbuf = Encoding.ASCII.GetBytes("Hello World!");  
        IPEndPoint ep = new IPEndPoint(broadcast, 11000);  
  
        s.SendTo(sendbuf, ep);  
  
        Console.WriteLine("Message sent to the broadcast address");  
    }  
}  

Listener

using System;  
using System.Net;  
using System.Net.Sockets;  
using System.Text;  
  
public class UDPListener  
{  
    private const int listenPort = 11000;  
  
    private static void StartListener()  
    {  
        UdpClient listener = new UdpClient(listenPort);  
        IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);  
  
        try  
        {  
            while (true)  
            {  
                Console.WriteLine("Waiting for broadcast");  
                byte[] bytes = listener.Receive(ref groupEP);  
  
                Console.WriteLine($"Received broadcast from {groupEP} :");  
                Console.WriteLine($" {Encoding.ASCII.GetString(bytes, 0, bytes.Length)}");  
            }  
        }  
        catch (SocketException e)  
        {  
            Console.WriteLine(e);  
        }  
        finally  
        {  
            listener.Close();  
        }  
    }  
  
    public static void Main()  
    {  
        StartListener();  
    }  
}  

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