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udpclient receives broadcast only locally (c#, Unity)

I want to receive a UDP message which was broadcasted to 255.255.255.255 with a UdpClient within Unity.
But whatever combination of settings I try, it only receives a message, if it was sent from localhost.
I have tried fitted example code from these resources, non worked:
https://gist.github.com/michaelosthege/857acac92b8ee689a6bb30d5bf23d9f6
C# UDP Broadcast and receive example
UdpClient receive on broadcast address
How to do Network discovery using UDP broadcast
I'm running the Code below a task.
private void Listen()
{
udpClient = new UdpClient(9000);
//udpClient.Client.Bind(new IPEndPoint(IPAddress.Any, 9000));
//udpClient.EnableBroadcast = true;
//udpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
//udpClient.ExclusiveAddressUse = false;
//broadcastAddress = new IPEndPoint(IPAddress.Any, 9000);
//udpClient.Client.Bind(broadcastAddress);
//udpClient.Connect(broadcastAddress);
//var from = new IPEndPoint(IPAddress.Any, 9000);
var from = new IPEndPoint(0, 0);
while (true)
{
var receive = udpClient.Receive(ref from);
var msg = Encoding.UTF8.GetString(receive);
Debug.Log($"Received message \"{msg}\"");
Debug.Log($"from {from} ({from.Address})");
}
}
I have used several of the commented lines in combination.
When I send something from within the same Application to 255.255.255.255 with another UdpClient on port 9000, it works as expected.
When I send something from any other machine on the network to 255.255.255.255
any machine in the network receives it (checking with PacketSender on osx devices)
On the windows machine I'm developing this application on, the message is received by UdpSenderReceiver
But the udpClient from within Unity does not receive anything - and the Firewall does not ask or tell me anything.
What could be the issue here?

Apparently Windows Defender by default blocks the Unity Editor (but not UdpSenderReceiver).
I had to resolve it by Admitting the Unity Editor on the public domain
The Rules for
Unity 2019.3.3f1 Editor
Unity 2019.3.4f1 Editor
had been present and were not modified.
I modified the Rule for Unity 2019.2.4f1 Editor in order to allow access from the public domain (I simply allowed all domains).

UDP networking with multiple network

I'm currently developing a network application on my machine with 2 network interfaces with the following setup -
I want to send UDP message by using the first configuration with IP 192.168.1.2.
using (var udpClient = new UdpClient(5556))
{
udpClient.Connect(IPAddress.Parse("192.168.1.2"), 5556);
// DO STUFF
}
When I try this I get the following error -
No connection could be made because the target machine actively
refused it
Strange this is that when I disable my other network that this works perfectly but with 2 connections (LAN & WiFi) it doesn't work anymore...
I guess that it is sending on wrong adapter?
Is this because my Default gateway is the same or what am I doing wrong?
I'm new to developing network-based applications...

You have to specify an IPEndPoint with networking card IP like this:
var endpoint = new IPEndPoint(IPAddress.Parse("192.168.1.2"), portNum);
UdpClient client = new UdpClient(endpoint);

You are not telling UdpClient which IP to use.
UdpClient has a constructor that can take an IPEndPoint.
const string ip = "192.168.1.2";
const int port = 5556;
var listenEndpoint = new IPEndPoint(IPAddress.Parse(ip), port);
var udpClient = new UdpClient(listenEndpoint);

I'm not that good in C# but I think I understand the problem. You are binding your udpClient to port 5556 but you're not specifying the IP address. The OS will select the IP address for you. I suppose it could be either 192.168.1.2 or 192.168.1.5, you cannot tell which one.
Then with the same udpClient you are trying to connect to a remote host listening on 192.168.1.2, port 5556. And probably nobody is listening there. This is why you receive the error.
I would do the following (sorry for my bad C# skills):
Have two udpClient's, in one thread or program/process:
var udpClient1 = new UdpClient("192.168.1.2", 5556);
This one will listen on IP addres 192.168.1.2, port 5556.
in second thread or program/process:
var udpClient2 = new UdpClient(); //doesn't matter which (IP, port) the OS will bind it to.
udpClient2.Connect(IPAddress.Parse("192.168.1.2"), 5556); //connect to peer/server listening in (IP=192.168.1.2, port=5556)
You could handle both udpClient1 and udpClient2 in the same thread also.
The important is that if you connect to and (IP, port) there has to be some application/process listening there. Otherwise, the remote host will send an ICMP message indicating the datagram cannot be delivered. The connection is refused.

Troubleshooting UDP Code

I'm working on a system to send data between peers on a network. One app is written in Java for the Android. The other app is written in C# on the PC.
I wrote code in Java on the Android to send UDP datagrams. And I wrote C# code to both send and receive datagrams. I tried to send messages from Android to PC. I could see the message in WireShark but not in my program. So, I put my program on a second PC. I succeeded in sending a message from my PC to the second one. But when I tried to send a message from seond PC back to mine it failed. I could see it in WireShark on my PC but not my application. Im at a loss for what to try next. Do you have any suggestions? Why would the UDP packet be visible in WireShark but not my application?
Here is my code.
//C# code on PC
//Sender
sending_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, rotocolType.Udp);
send_to_address = IPAddress.Parse(strIPAddress);
sending_end_point = new IPEndPoint(send_to_address, intPort);
sending_socket.EnableBroadcast = true;
byte[] bytMessage = Encoding.ASCII.GetBytes(strMessage);
sending_socket.SendTo(bytMessage, sending_end_point);
//Listener
UdpClient listener = new UdpClient(listenPort);
IPEndPoint groupEP = new IPEndPoint(IPAddress.Any, listenPort);
byte[] bytReceiveDataByteArray;
try
{
listener.EnableBroadcast = true;
while (isRunning)
{
//listen for data from sender
bytReceiveDataByteArray = listener.Receive(ref groupEP);
//Fire an event to send the data to the hosting code
if (DataReceived != null)
{
DataReceivedEventArgs e = new DataReceivedEventArgs(bytReceiveDataByteArray);
DataReceived(this, e);
}
}
}
//Java code on Android
DatagramSocket socket = new DatagramSocket();
InetAddress serverIP = InetAddress.getByName(strIpAddress);
byte[] outData = (strMsg).getBytes();
DatagramPacket out = new DatagramPacket(outData,outData.length, serverIP,50005);
socket.send(out);
socket.close();
Thanks,
Mike

If I understand the problem correct when your program runs on a specific PC (lets call it "Windows1") it never receives the UDP packets. It will not receive them from Java Android or from C# code running on a different PC ( lets call it "Windows2").
However when you run your program on "Windows2" it DOES receive messages from "Windows1". Sounds like you have the firewall enabled on "Windows1" and do not have an exception for UDP port 50005. On "Windows2" your firewall is turned off or has the exception for 50005 and this is why it receives messages from "Windows1".
Note that since UDP is not connection oriented, firewall errors will not cause the usual connection timed out error. The messages are just dropped and you never get an error.

TcpClient connect fails with IPv6Any

The problem is, the following code works well if IPAddress.Any was given as a parameter, but throws an error if `IPAddress.IPv6Any is used.
I receive error #10057
Socket is not connected.
A request to send or receive data was disallowed because the socket is
not connected and (when sending on a datagram socket using
sendto) no address was supplied. Any other type of operation might
also return this error—for example, setsockopt setting SO_KEEPALIVE if
the connection has been reset.
Why does it fails to work as IPv6Any? I'm pretty sure it's not the firewall, since the port remains the same and it works with IPv4 (and my firewall should pass any requests made by my application).
To short up the code, it's something like this:
The Listener:
listener = new TcpListener(IPAddress.IPv6Any, portNr);
listener.AllowNatTraversal(true);
listener.Start();
listener.BeginAcceptTcpClient(this.AcceptClient, null);
The Client:
client = new TcpClient();
client.NoDelay = true;
try
{
this.client.Connect(ip, port); //ip = "localhost" when connecting as server
}
catch (Exception ex)
{
FileLogger.LogMessage(ex);
Disconnect();
}
I'm trying to set up the "server-side" of the TCP-connection.
What I do is that I start a listener at localhost, and then connect to it as a client (and allow others to join as clients as well).
What I'm trying to achieve with this is direct addressability of this TCP server, following this article: http://blogs.msdn.com/b/ncl/archive/2009/07/27/end-to-end-connectivity-with-nat-traversal-.aspx
The reason I'm doing this is that I want person A to be able to connect to a person B when they both are behind NAT routers.

I know this answer comes a bit late, but I also had this issue and it was client related. The problem is, that your provided code...
client = new TcpClient();
... creates an IPv4-Instance of the TcpClient that is not capable of interpreting IPv6-Addresses. So if you already have the IP address at the moment of initialization, try to initialize your TcpClient like this:
TcpClient client = new TcpClient(ip.AddressFamily);
If the variable ip is a string, you need to convert it to type IPAddress first:
IPAddress iAddr = IPAddress.Parse(ip);
Actually a IPv6-TcpClient seems to be compatible to IPv4-Addresses as well, so you can also initialize your client as follows:
TcpClient client = new TcpClient(AddressFamily.InterNetworkV6)
Whilst the upper suggestions seem to be the cleanest ones, the bottom suggestion seems to be the more universal one. At the end it's up to your preferences.

I solved a similar issue where the following line would only block connections coming from IPv4 addresses:
listener = new TcpListener(IPAddress.IPv6Any, portNr);
It seems the socket when configured to accept IPv6 connections, by default, accepts ONLY IPv6 connections. To fix this problem i had to update my code to this:
listener.Server.SetSocketOption(SocketOptionLevel.IPv6, SocketOptionName.IPv6Only, false);
listener.Start();

When you use TcpClient.Connect(string, int) you make it possible to break because of DNS resolution.
Though Microsoft documents that IPv6 address will be tried first, the resolution may only return IPv4 addresses.
http://msdn.microsoft.com/en-us/library/8s2yca91.aspx
Therefore, can you try to call TcpClient.Connect(IPAddress.IPv6Loopback, port) on client side to test if it works?

IPAddress.Loopback == FAIL
IPAddress.IPv6Loopback == SUCCESS
Perhaps localhost is mapping to the IPv4 Loopback Address in your case?

UdpClient receive on broadcast address

In c# I am using the UdpClient.Receive function:
public void StartUdpListener(Object state)
{
try
{
udpServer = new UdpClient(new IPEndPoint(IPAddress.Broadcast, 1234));
}
catch (SocketException ex)
{
MessageBox.Show(ex.ErrorCode.ToString());
}
IPEndPoint remoteEndPoint = null;
receivedNotification=udpServer.Receive(ref remoteEndPoint);
...
However I am getting a socket exception saying that the address is not available with error code 10049
What do I do to negate this exception?

Here's the jist of some code I am currently using in a production app that works (we've got a bit extra in there to handle the case where the client are server apps are running on a standalone installation). It's job is to receive udp notifications that messages are ready for processing. As mentioned by Adam Alexander your only problem is that you need to use IPAddress.Any, instead of IPAddress.Broadcast. You would only use IPAddress.Broadcast when you wanted to Send a broadcast UDP packet.
Set up the udp client
this.broadcastAddress = new IPEndPoint(IPAddress.Any, 1234);
this.udpClient = new UdpClient();
this.udpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
this.udpClient.ExclusiveAddressUse = false; // only if you want to send/receive on same machine.
And to trigger the start of an async receive using a callback.
this.udpClient.Client.Bind(this.broadcastAddress);
this.udpClient.BeginReceive(new AsyncCallback(this.ReceiveCallback), null);
Hopefully this helps, you should be able to adapt it to working synchronously without too much issue. Very similar to what you are doing. If you're still getting the error after this then something else must be using the port that you are trying to listen on.
So, to clarify.
IPAddress.Any = Used to receive. I want to listen for a packet arriving on any IP Address.
IPAddress.Broadcast = Used to send. I want to send a packet to anyone who is listening.

for your purposes I believe you will want to use IPAddress.Any instead of IPAddress.Broadcast. Hope this helps!

That error means the protocol cant bind to the selected IP/port combination.
I havent used UDP broadcast in ages, but I do recall you need to use different IP ranges.

There's nothing wrong with the way you have configured your UdpClient. Have you tried a different port number? Perhaps 1234 is already in use on your system by a different app.