UDP works one way but not the other way

[zedrummer]

Hello
To detect the server for a connection, the server broadcasts its address through this UDP code sent each second:

        private static void BroadcastDiscovery()
        {
            while (isBroadcasting)
            {
                byte[] discoveryData = Encoding.UTF8.GetBytes("Server_IP: " + localIpAddress);
                udpClient.Send(discoveryData, discoveryData.Length, new IPEndPoint(IPAddress.Broadcast, DISCOVERY_PORT));

                Thread.Sleep(1000); // Wait for 1000 milliseconds before sending the next broadcast
            }
        }        // Function to get the local IP address

Then the clients check the messages broadcast with this code called over and over:

        public static string ListenForDiscoveryMessages()
        {
            udpClient = new UdpClient(DISCOVERY_PORT);
            udpClient.EnableBroadcast = true;
            try
            {
                udpClient.Client.ReceiveTimeout = 2000;

                while (true)
                {
                    IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, DISCOVERY_PORT);
                    byte[] receivedData = udpClient.Receive(ref remoteEndPoint);

                    string message = Encoding.UTF8.GetString(receivedData);
                    Debug.WriteLine($"Received discovery message: {message}");
                    if (message.Substring(0, DISCOVERY_MESSAGE.Length) == DISCOVERY_MESSAGE)
                    {
                        Server_IP = message.Substring(DISCOVERY_MESSAGE.Length);
                        udpClient.Close();
                        return Server_IP;
                    }
                }
            }
            catch (SocketException ex)
            {
                if (ex.SocketErrorCode == SocketError.TimedOut)
                {
                    Debug.WriteLine("Discovery message reception timed out.");
                }
                else
                {
                    Debug.WriteLine($"SocketException: {ex.Message}");
                }
            }
            udpClient.Close();
            return "";
        }

I have a desktop connected to the router (local network) via Ethernet and a laptop connected via Wifi. If I start the server on the laptop, the message is received by the desktop, but if I start the server on the desktop, I always get a time out message. I've checked the firewall and for both computers, the app is unblocked. Any idea, please?

Thanks
David

 

[Skydiver]

This doesn't sound like a VS.NET issue. Sounds more like a networking issue. Going to try to move to a more appropriate forum...

 

[zedrummer]

OK, sorry for posting at the wrong spot

 

[Skydiver]

Attach the laptop to the router via Ethernet as well to get rid of one variable. (Some routers automatically try to isolate the WiFi connected machines from Ethernet connected machines and only select packets through as a security measure.)

Next thing is to start running WireShark to see if the broadcast messages are actually getting out unto the network.

 

[zedrummer]

Connecting via Ethernet the laptop didn't change anything.
I am installing WireShark, I've never used it, if you could provide some help, please?

 

[Skydiver]

If connecting via Ethernet didn't work either, I suspect that this isn't a C# issue but rather a machine configuration issue. Perhaps you have an extra anti-virus layer that is separate from the Windows firewall that is running on the desktop?

Sorry, I can't help with the WireShark tutorial. Hopefully you can find a tutorial online.

 

[zedrummer]

Thanks a lot, just starting WireShark and analyzing what is displayed, I see that the desktop doesn't seem to broadcast, I'm gonna investigate this way thanks a lot!

 

[zedrummer]

OK I found the problem: I had several different ethernet network on the desktop and I suppose it was not broadcasting on the same as the laptop. Deactivating the unneeded networks makes the code perfectly work. Thanks for your help.