C# Send UDP Wake On Lan packet to a computer connected from VPN

Question

If I am connected to the VPN from my local network in which the computer to which I want to send the package is also connected, it works for me, but if I am connected, for example, to mobile data and connected to the VPN, it does not perform WakeOnLan, no I don't get any exceptions or anything, everything runs fine, but the remote computer that I want to pass on its MAC does not turn on.

    public static async Task WakeOn(string macAddress)
        {
            byte[] magicPacket = BuildMagicPacket(macAddress);
            foreach (NetworkInterface networkInterface in NetworkInterface.GetAllNetworkInterfaces().Where((n) =>
                n.NetworkInterfaceType != NetworkInterfaceType.Loopback && n.OperationalStatus == OperationalStatus.Up))
            {
                IPInterfaceProperties iPInterfaceProperties = networkInterface.GetIPProperties();
                foreach (MulticastIPAddressInformation multicastIPAddressInformation in iPInterfaceProperties.MulticastAddresses)
                {
                    IPAddress multicastIpAddress = multicastIPAddressInformation.Address;
                    if (multicastIpAddress.ToString().StartsWith("ff02::1%", StringComparison.OrdinalIgnoreCase)) // Ipv6: All hosts on LAN (with zone index)
                    {
                        UnicastIPAddressInformation unicastIPAddressInformation = iPInterfaceProperties.UnicastAddresses.Where((u) =>
                            u.Address.AddressFamily == AddressFamily.InterNetworkV6 && !u.Address.IsIPv6LinkLocal).FirstOrDefault();
                        if (unicastIPAddressInformation != null)
                        {
                            await SendWakeOnLan(unicastIPAddressInformation.Address, multicastIpAddress, magicPacket);
                            break;
                        }
                    }
                    else if (multicastIpAddress.ToString().Equals("224.0.0.1")) // Ipv4: All hosts on LAN
                    {
                        UnicastIPAddressInformation unicastIPAddressInformation = iPInterfaceProperties.UnicastAddresses.Where((u) =>
                            u.Address.AddressFamily == AddressFamily.InterNetwork && !iPInterfaceProperties.GetIPv4Properties().IsAutomaticPrivateAddressingActive).FirstOrDefault();
                        if (unicastIPAddressInformation != null)
                        {
                            await SendWakeOnLan(unicastIPAddressInformation.Address, multicastIpAddress, magicPacket);
                            break;
                        }
                    }
                }
            }
        }
        static byte[] BuildMagicPacket(string macAddress) // MacAddress in any standard HEX format
        {
            macAddress = Regex.Replace(macAddress, "[: -]", "");
            byte[] macBytes = new byte[6];
            for (int i = 0; i < 6; i++)
            {
                macBytes[i] = Convert.ToByte(macAddress.Substring(i * 2, 2), 16);
            }

            using (MemoryStream ms = new MemoryStream())
            {
                using (BinaryWriter bw = new BinaryWriter(ms))
                {
                    for (int i = 0; i < 6; i++)  //First 6 times 0xff
                    {
                        bw.Write((byte)0xff);
                    }
                    for (int i = 0; i < 16; i++) // then 16 times MacAddress
                    {
                        bw.Write(macBytes);
                    }
                }
                return ms.ToArray(); // 102 bytes magic packet
            }
        }
        static async Task SendWakeOnLan(IPAddress localIpAddress, IPAddress multicastIpAddress, byte[] magicPacket)
        {
            using (UdpClient client = new UdpClient(new IPEndPoint(localIpAddress, 0)))
            {
                await client.SendAsync(magicPacket, magicPacket.Length, multicastIpAddress.ToString(), 9);
            }
        }

Answer 1

UDP uses broacasts, broadcasts are not forwarded outside of network, you may need to add exceptions. UDP is connectionless, and when you are wanting to talk UDP from seperate networks, you will find that difficult.

Here is some more info:

https://techhub.hpe.com/eginfolib/networking/docs/switches/WB/15-18/5998-8166_wb_2920_mrg/content/ch03s10.html