We Keep Coding

C# Getting the IP Address of the client which the UDP server socket received data from

I have a very strange problem. I'm not able to find the IP Address of the client which my server receives data from. Below is my UDP Listener class.
The IPPacketInformation does not contain the IP. The clientEndPoint which I reference in my EndReceiveMessageFrom does neither.
When I
Console.Writeline(((IPEndPoint)clientEndPoint).Address);
I get the IP Address of the server. I have the server hosted on my own machine so I get my own IP Address. When I try to access clientEndPoint.remoteEndPoint it throws an error because the socket isn't connected (due to being UDP).
So basically, a client from an external IP is able to send data, but I can't answer the client since I'm not able to retrieve it's IP. Any help is appreciated!
public class UdpListener
{
private Socket s;
public byte[] ReceiveBuffer = new byte[2048];
public UdpListener()
{
s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.PacketInformation, true);
s.Bind(new IPEndPoint(IPAddress.Any, 36200));
}
public void Listen()
{
try
{
EndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
s.BeginReceiveMessageFrom(ReceiveBuffer, 0, ReceiveBuffer.Length, SocketFlags.None, ref remoteEndPoint, Recv, s);
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
throw;
}
}
private void Recv(IAsyncResult res)
{
try
{
Socket receiveSocket = (Socket)res.AsyncState;
EndPoint clientEndPoint = new IPEndPoint(IPAddress.Any, 0);
IPPacketInformation packetInfo;
SocketFlags flags = SocketFlags.None;
int udpMessageLength = receiveSocket.EndReceiveMessageFrom(res, ref flags, ref clientEndPoint, out packetInfo);
byte[] udpMessage = new byte[udpMessageLength];
Array.Copy(ReceiveBuffer, udpMessage, udpMessageLength);
Console.WriteLine(
"{0} bytes received from {1} to {2}",
ReceiveBuffer,
clientEndPoint,
packetInfo.Address
);
EndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, ((IPEndPoint)receiveSocket.LocalEndPoint).Port);
s.BeginReceiveMessageFrom(ReceiveBuffer, 0, ReceiveBuffer.Length, SocketFlags.None, ref remoteEndPoint, Recv, s);
//Process data
RaiseDataReceived(new ReceivedDataArgs(packetInfo.Address, ((IPEndPoint)clientEndPoint).Port, udpMessage));
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
throw;
}
}
public delegate void DataReceived(ReceivedDataArgs args);
public event DataReceived DataReceivedEvent;
private void RaiseDataReceived(ReceivedDataArgs args)
{
DataReceivedEvent?.Invoke(args);
}
}
I've tried to disable my firewall but that does not help. I've also done Port Forwarding on my router thus I can receive data from external clients.
EDIT to clarify the problem:
Server hosted on my machine behind a NAT with public IP 214.214.214.214.
The client is another machine, behind another NAT with public IP 910.910.910.910.
The client sends a message to the server, server receives it and able to read the content. When server get the IPEndPoint of the client, the displayed IP is 214.214.214.214 (IP of the server, not the Client)
EDIT Maybe I should say that I wasn't able to receive messages from clients on external networks until I ordered a "Dynamic IP" from my ISP. Still can't get the public IP of the source.
EDIT When using Wireshark and sniff a packet sent from external client to my server I can see it's the wrong src IP as well. In the picture below the src IP is my server IP and not the IP of the client that sent the data.

After several days of reading everything I possibly could on routers, network and writing different examples of Receive, ReceiveFrom, ReceiveMessageFrom, BeginReceive, BeginReceiveFrom, BeginReceiveMessageFrom, and ReceiveAsync - I've solved my issue.
I changed my router. I can now get the source IP of the external client using a very old router. The router I was using before was a new Docsis 3.1.
Why it works with an old router, I don't know, but for some reason, the Docsis 3.1 changed the source IP to its own IP before letting the UDP message to my machine.

With using the UdpClient class you can actually retrieve the remote endpoint when receiving a message.
I have used a solution like the following to solve this task:
public void StartServer()
{
var udpServer = new UdpClient(new IPEndPoint(IPAddress.Any, ConnectionInformation.DETECTION_PORT));
udpServer.BeginReceive(new AsyncCallback(detectionCallback), udpServer);
}
private void detectionCallback(IAsyncResult ar)
{
var client = (ar.AsyncState as UdpClient);
if (client.Client == null) return;
var endPoint = new IPEndPoint(IPAddress.Any, ConnectionInformation.DETECTION_PORT);
var bytes = client.EndReceive(ar, ref endPoint);
Debug.WriteLine($"Detection request from: {endPoint}");
}

Sending broadcast packet issue

I am currently working on a C#/Android client/server project.
I have a server application, running C# on Windows, which sends a broadcast message on port 8000.
The idea is the client application (Android) receives the broadcast and then shows the server hostname and IP, from the message sent via the broadcast, on the Android device for the user to select.
Below is how I am attempting to do the broadcast.
int availableTCPSocket = 0;
try
{
//UdpClient udp = new UdpClient();
Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Broadcast, 1);
availableTCPSocket = getAvailableTCPSocket();
//IPEndPoint endpoint = new IPEndPoint(IPAddress.Broadcast, BROADCAST_PORT);
IPEndPoint endpoint = new IPEndPoint(IPAddress.Parse("192.168.1.255"), BROADCAST_PORT);
XmlGenerator xmlGenerator = new XmlGenerator();
xmlGenerator.addStartElement("ServerInformation");
xmlGenerator.addElementString("Hostname", Dns.GetHostName());
NetworkAdapterDetails networkAdapterDetails = getNetworkAdapterDetails();
xmlGenerator.addElementString("IP_Address", networkAdapterDetails.ipAddress);
xmlGenerator.addElementString("MAC_Address", networkAdapterDetails.macAddress);
xmlGenerator.addElementString("AvailableTCPSocket", availableTCPSocket.ToString());
xmlGenerator.addEndElement();
xmlGenerator.flushAndCloseXmlWriter();
string udpData = xmlGenerator.returnXml();
byte[] sendBytes = Encoding.ASCII.GetBytes(udpData);
while (true)
{
//udp.Send(sendBytes, sendBytes.Length, endpoint);
socket.SendTo(sendBytes, endpoint);
Console.WriteLine("Broadcast Sent");
System.Threading.Thread.Sleep(5000);
}
}
catch (Exception ex)
{
Console.WriteLine("Broadcast Sender Exception: {0}", ex.Message);
}
If I set the endpoint to be IPAddress.Broadcast it says it is 255.255.255.255 but my devices never receive the broadcast.
If I change the endpoint to be hardcoded to 192.168.1.255 then my devices receive the broadcast.
So because of this I have two questions.
If I use IPAddress.Broadcast why don't my devices receive anything if this is supposed to be broadcast.
If 192.168.1.255 is the correct broadcast address, how can I find out what the addresss should be dynamically, the idea is the server will be provided for download so has to work on different network configurations where 192.168.1.255 might not be the correct address.
It also takes a long time for the device to receive the packet, the server writes to the console each time its looped round and sends the broadcast but it takes about 4 or 5 broadcasts to be sent before the devices receives it. Its on a WIFI network but strong signal on all devices, 60mb download on the internet and 2ms ping between router and devices.
Thanks for any help you can provide.

Windows 7 handles 255.255.255.255 broadcast in a different way. More info here: Send UDP broadcast on Windows 7
use subnet broadcast instead of 255.255.255.255
Code to Get subnet broadcast address
public static IPAddress GetBroadcastAddress(this IPAddress address, IPAddress subnetMask)
{
byte[] ipAdressBytes = address.GetAddressBytes();
byte[] subnetMaskBytes = subnetMask.GetAddressBytes();
if (ipAdressBytes.Length != subnetMaskBytes.Length)
throw new ArgumentException("Lengths of IP address and subnet mask do not match.");
byte[] broadcastAddress = new byte[ipAdressBytes.Length];
for (int i = 0; i < broadcastAddress.Length; i++)
{
broadcastAddress[i] = (byte)(ipAdressBytes[i] | (subnetMaskBytes[i] ^ 255));
}
return new IPAddress(broadcastAddress);
}

You need to enable sending broadcast messages on the socket with socket.EnableBroadcast = true. Then you should be able to send them to 255.255.255.255 just fine.
Reference: http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.enablebroadcast(v=vs.110).aspx

Over wi-fi sometimes doesn't allow the packets send over 255.255.255.255 depending on the security settings in it. Find the broadcast address of the network at run time & use it. You can get the broadcast network address of any network by performing the below operation.
broadcastaddress = (ipaddressofthesystem & netmask) & ~netmask;
Also as an alternative you should consider using multicast address.

How to detect destination IP address from UDP packets using UDPClient Class

I am working on the application which send and receive messages on UDP between client app and server app.
On my server I have 4 different network cards, e.g. nic1 = 169.524.15.12, nic2 = 169.524.15.65, etc. My DNS is point to nic2. The client app resolves the DNS and send data to nic2. However my server app sometime respond to client from nic1.
I'm using an UdpClient to listen for incoming packets.
This is my server application code:
objSocketServer = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
EndPoint objEndPointOfServer = new IPEndPoint(IPAddress.Any, 5000);
objSocketServer.Bind(objEndPointOfServer);
objSocketServer.BeginReceiveFrom(_arrReceivedDataBuffer, 0, BUFSIZE - 1, SocketFlags.None, ref objEndPointOfServer, DoReceiveFromClient, objSocketServer);
private void DoReceiveFromClient(IAsyncResult objIAsyncResult)
{
try
{
// Get the received message.
_objSocketReceivedClient = (Socket)objIAsyncResult.AsyncState;
EndPoint objEndPointReceivedClient = new IPEndPoint(IPAddress.Any, 0);
// Received data.
int intMsgLen = _objSocketReceivedClient.EndReceiveFrom(objIAsyncResult, ref objEndPointReceivedClient);
byte[] arrReceivedMsg = new byte[intMsgLen];
Array.Copy(_arrReceivedDataBuffer, arrReceivedMsg, intMsgLen);
// Client port.
// Get and store port allocated to server1 while making request from client to server.
int _intClientServer1Port = ((IPEndPoint)objEndPointReceivedClient).Port;
// Send external ip and external port back to client.
String strMessage = ((IPEndPoint)objEndPointReceivedClient).Address.ToString() + ":" + _intClientServer1Port.ToString();
byte[] arrData = Encoding.ASCII.GetBytes(strMessage);
objSocketServer.SendTo(arrData, arrData.Length, SocketFlags.None, objEndPointReceivedClient);
// Start listening for a new message.
EndPoint objEndPointNewReceivedClient = new IPEndPoint(IPAddress.Any, 0);
objSocketServer.BeginReceiveFrom(_arrReceivedDataBuffer, 0, _arrReceivedDataBuffer.Length, SocketFlags.None, ref objEndPointNewReceivedClient, DoReceiveFromClient, objSocketServer)
}
catch (SocketException sx)
{
objSocketServer.Shutdown(SocketShutdown.Both);
objSocketServer.Close();
}
}
}
Is there any way so that in code, I can detect that I have received packet on which IP address on server and revert with the response with same IP?
Arguably, I could resolve DNS in server app as well and make sure that my server app only listen to IP on which client app is sending packets, however that approach will not work for me when my server app have to listen on > 1 IP.

The SendTo command will use the appropriate NIC (aka, local interface) for the destination address provided. The system metrics determine that. It's not something you set in your code. To view the system metrics, run the command netstat -rn and look at the Interface column. You many need to adjust those if you have a tie. You can enumerate them in code as well using GetAllNetworkInterfaces() and bind to a specific one (if that is what you wanted).

Receiving udp packet on designated network card c#

I have 3 different network cards each with their individual responsibility. Two of the cards are receiving packets from a similar device (plugged directly into each individual network card) which sends data on the same port. I need to save the packets knowing which device they came from.
Given that I am required to not specify the ip address of the devices sending me the packets, how can I listen on a given network card? I am allowed to specify a static ip address for all 3 nics if needed.
Example: nic1 = 169.254.0.27, nic2 = 169.254.0.28, nic3 = 169.254.0.29
Right now I have this receiving the data from nic1 and nic2 without knowing which device it came from.
var myClient = new UdpClient(2000) //Port is random example
var endPoint = new IPEndPoint(IPAddress.Any, 0):
while (!finished)
{
byte[] receivedBytes = myClient.Receive(ref endPoint);
doStuff(receivedBytes);
}
I can't seem to specify the static ip address of the network cards in a manner which will allow me to capture the packets from just one of the devices. How can I separate these packets with only the knowledge that they are coming in on two different network cards?
Thank you.

You're not telling the UdpClient what IP endpoint to listen on. Even if you were to replace IPAddress.Any with the endpoint of your network card, you'd still have the same problem.
If you want to tell the UdpClient to receive packets on a specific network card, you have to specify the IP address of that card in the constructor. Like so:
var listenEndpoint = new IPEndPoint(IPAddress.Parse("192.168.1.2"), 2000);
var myClient = new UdpClient(listenEndpoint);
Now, you may ask "What's the ref endPoint part for when I'm calling myClient.Receive(ref endPoint)?" That endpoint is the IP endpoint of the client. I would suggest replacing your code with something like this:
IPEndpoint clientEndpoint = null;
while (!finished)
{
var receivedBytes = myClient.Receive(ref clientEndpoint);
// clientEndpoint is no longer null - it is now populated
// with the IP address of the client that just sent you data
}
So now you have two endpoints:
listenEndpoint, passed in through the constructor, specifying the address of the network card you want to listen on.
clientEndpoint, passed in as a ref parameter to Receive(), which will be populated with the client's IP address so you know who is talking to you.

Check this out this:
foreach (NetworkInterface netInterface in NetworkInterface.GetAllNetworkInterfaces())
{
Console.WriteLine("Name: " + netInterface.Name);
Console.WriteLine("Description: " + netInterface.Description);
Console.WriteLine("Addresses: ");
IPInterfaceProperties ipProps = netInterface.GetIPProperties();
foreach (UnicastIPAddressInformation addr in ipProps.UnicastAddresses)
{
Console.WriteLine(" " + addr.Address.ToString());
}
Console.WriteLine("");
}
Then you can choose on which address start listening.

look, if you create your IPEndPoint in the following way it must work:
IPHostEntry hostEntry = null;
// Get host related information.
hostEntry = Dns.GetHostEntry(server);
foreach(IPAddress address in hostEntry.AddressList)
{
IPEndPoint ipe = new IPEndPoint(address, port);
...
try to do not pass 0 as port but a valid port number, if you run this code and break the foreach after the first iteration you will have created only 1 IPEndPoint and you can use that one in your call to: myClient.Receive
notice that the UdpClient class has a member calledd Client which is a socket, try to explore the properties of that object as well to find out some details, I have found the code I gave you here: http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.aspx

C# Getting sender address from UDP message

I have an embedded Ethernet interface (Lantronix XPort) that responds to a UDP broadcast with its identifying information.
I am able to multicast the "magic packet" and datagrams are received by the listener correctly, however I also need to find out what IP Address send that response datagram. If it were TCP, I would do socket.RemoteEndPoint, but that throws an exception when applied to a UDP socket.
public class Program
{
public static void Main(string[] args)
{
// magic packet
byte[] magicPacket = new byte[4] { 0, 0, 0, 0xf6 };
// set up listener for response
Socket sendSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
// EDIT: Also, had to add this to for it to broadcast correctly
sendSocket.EnableBroadcast = true;
IPEndPoint listen_ep = new IPEndPoint(IPAddress.Any, 0);
sendSocket.Bind(listen_ep);
// set up broadcast message
EndPoint send_ep = new IPEndPoint(IPAddress.Parse("192.168.255.255"), 30718);
sendSocket.SendTo(magicPacket, magicPacket.Length, SocketFlags.None, send_ep);
DateTime dtStart = DateTime.Now;
while (true)
{
if (sendSocket.Available > 0)
{
byte[] data = new byte[2048];
// throws SocketException
//IPEndPoint ip = sendSocket.RemoteEndPoint as IPEndPoint;
sendSocket.Receive(data, SocketFlags.None);
if (data.Length > 4)
{
PrintDevice(data);
}
}
if (DateTime.Now > dtStart.AddSeconds(5))
{
break;
}
Console.WriteLine(".");
Thread.Sleep(100);
}
// wait for keypress to quit
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
Any thoughts? Is there a better strategy to reading the response datagrams that would let me ascertain the Remote IP Address?
EDIT:
As is typical, the minute I post on SO, a moment of clarity hits me.
Turns out I can just do this:
EndPoint remote_ep = new IPEndPoint(IPAddress.Any, 0);
// Use ReceiveFrom instead of Receieve
//sendSocket.Receive(data, SocketFlags.None);
sendSocket.ReceiveFrom(data, ref remote_ep);
And remote_ep now contains the remote endpoint information!

Take a look at ReceiveFrom instead of Receive, it will let you pass in a reference to an Endpoint.

What about Asynchronous socket?I didn't find any way to get the remote IP address. (Asynchronous method ReceiveFromAsync is my only option in wp8)

EndPoint remote_ep = new IPEndPoint(IPAddress.Any, 0); // Use ReceiveFrom instead of
sendSocket.Receive(data, SocketFlags.None);
sendSocket.ReceiveFrom(data, ref remote_ep);
i think it works for IP but it fails for port number
if you would notice
try chaging 0 to something else like 6530 4expl
it system will would generate it's random port number
Any ideas to why is it ?
P.S. Any ideas how can i change my user name here .... ?
FOUND IT : the abstract class only needed for representation of port it is in value not out
since there's no bind done before hand this operation ref EndPoint needed to represent the sender. Meaning that it is there to show senders port and IP not to specify from where to get the communication. And EndPoint instantiation is really just a formality seems like it is overriden by system with senders address anyway. I think it has to do somethign with the way UDP protocol works.
But all in all the ref EndPoint is there only shows where u got the packet from and only it does not specify where u want u'r commuicatino to be from.