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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).

Sending/receiving UDP packets on thousands of port numbers

I have a set of requirements for a client/server application as listed below:
1) Program sends a statuscheck message to a host which is listening on a predefined UDP port. This message is sent on a source port number given by the OS.
2) The program needs to listen on the source port number initiated in step 1 to receive the response from the remote host. The program therefore must listen on thousands of port at the same time.
3) This process needs to be done for thousands of hosts per minute
Below I've created a sample example that sends a large number of requests to an Echo Server to mimic this behaviour. The problem that I'm facing is that although I close each socket after receiving data from the remote host, after about 16,000 requests an exception is thrown saying system lacked sufficient buffer space or queue was full.
What would be a way to achieve such requirements?
public void SendChecks()
{
IPEndPoint ip = new IPEndPoint(IPAddress.Parse("1.1.1.1"), 7);
for (int i = 0; i < 200000; i++)
{
Socket _UdpSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
stateobject so = new stateobject(_UdpSocket);
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint tempRemoteEP = (EndPoint)sender;
_UdpSocket.Bind(tempRemoteEP);
string welcome = "Hello";
byte[] data = new byte[5];
data = Encoding.ASCII.GetBytes(welcome);
_UdpSocket.BeginSendTo(data, 0, data.Length, SocketFlags.None, ip, new AsyncCallback(OnSend), _UdpSocket);
//Start listening to the message send by the user
EndPoint newClientEP = new IPEndPoint(IPAddress.Any, 0);
_UdpSocket.BeginReceiveFrom(so.buffer, 0, so.buffer.Length, SocketFlags.None, ref newClientEP, new AsyncCallback(DoReceiveFrom), so);
}
}
private void DoReceiveFrom(IAsyncResult ar)
{
try
{
stateobject so = (stateobject)ar.AsyncState;
Socket s = so.sock;
// Creates a temporary EndPoint to pass to EndReceiveFrom.
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint tempRemoteEP = (EndPoint)sender;
int read = s.EndReceiveFrom(ar, ref tempRemoteEP);
so.sb.Append(Encoding.ASCII.GetString(so.buffer, 0, read))
//All the data has been read, so displays it to the console.
string strContent;
strContent = so.sb.ToString();
Console.WriteLine(String.Format("Read {0} byte from socket" +"data = {1} ", strContent.Length, strContent));
s.Close();
s.Dispose();
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
}
private void OnSend(IAsyncResult ira)
{
Socket s = (Socket)ira.AsyncState;
Console.WriteLine("Sent Data To Sever on port {0}",((IPEndPoint)s.LocalEndPoint).Port);
s.EndSend(ira);
}
}

I think the best way to go in terms of performance and simplicity would be to simply use a single port number anywhere between:
1025 - 65553
Then when listening for thousands of messages from other peers they also send to a predefined known port number and you can process them asynchronously.
To listen to a known port number, in this case 60000:
mySocket.Bind(new IPEndPoint(IPAddress.Any, 60000));
Also do not close the socket after each operation! Keep it open and re-use it.
Properly written it would be walk in the park for .Net and the OS to handle your requirements.

C# UDP socket app to listen to messages from various sockets

I have a system monitor app that needs to listen to messages from various UDP sockets on another machine. The other sockets continuously send heartbeats to this given IP/port.
This exception gets thrown when calling BeginReceiveFrom:
"A request to send or receive data was disallowed because the socket is not connected and (when sending on a datagram socket using a sendto call) no address was supplied"
I shouldn't have to call connect because data is already getting sent to this ip endpoint. plus the data is coming from various sockets.
private Socket m_socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
private void Window_Loaded(object sender, RoutedEventArgs e)
{
// bind socket
// Establish the local endpoint for the socket.
// Dns.GetHostName returns the name of the
// host running the application.
IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[0];
m_localEndPoint = new IPEndPoint(ipAddress, 19018);
m_socket.Bind(m_localEndPoint);
m_socket.BeginReceiveFrom(m_data,
m_nBytes,
MAX_READ_SIZE,
SocketFlags.None,
ref m_localEndPoint,
new AsyncCallback(OnReceive),
null);
}
private void OnReceive(IAsyncResult ar)
{
int nRead = m_socket.EndReceiveFrom(ar, ref m_localEndPoint);
}

I was able to get the desired behavior with the UdpClient class.

Your problem was you were binding to the IP assigned to you, you should bind to IP you want receive from - in your case:
m_socket.Bind(new IPEndPoint(IPAddress.Any, 12345));

Unable to read incoming responses using raw sockets

I am trying to read a response from a website via code by listening to a raw socket, though so far I've only been able to read the outgoing requests sent by my computer rather than the incoming responses that I'm actually interested in.
How might I go about reading the incoming responses?
EDIT: Using Wireshark I've come to find that the data I'm looking for is being sent via TCP, I believe.
Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Unspecified);
IPAddress localIP = Dns.GetHostByName(Dns.GetHostName()).AddressList[0];
listener.Bind(new IPEndPoint(localIP, 0));
byte[] invalue = new byte[4] { 1, 0, 0, 0 };
byte[] outvalue = new byte[4] { 1, 0, 0, 0 };
listener.IOControl(IOControlCode.ReceiveAll, invalue, outvalue);
while (true)
{
byte[] buffer = new byte[1000000];
int read = listener.Receive(buffer);
if (read >= 20)
{
Console.WriteLine("Packet from {0} to {1}, protocol {2}, size {3}",
new IPAddress((long)BitConverter.ToUInt32(buffer, 12)),
new IPAddress((long)BitConverter.ToUInt32(buffer, 16)),
buffer[9],
buffer[2] << 8 | buffer[3]
);
}
}

port 0 says he will listen on all ports, i think you need to set ProtocolType.Unspecified to ProtocolType.IP instead.
new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Raw);
is for ipv6 from what i read on msdn only ProtocolType.IP is supported for ipv4 with raw sockets.
Also im thinking this is a connectionless socket right?
Reciveall wouldnt really have an affect unless thats the case.
if youre after the ip header u can get it by setting up the code like this:
Socket sck = new Socket( AddressFamily.InterNetwork , SocketType.Raw , ProtocolType.IP);
sck.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.HeaderIncluded, true);
hope this helps :)

I had a similar problem in my C++ program using basically the same raw sockets setup. In my case I can see incoming packets in the debug build, but not in a release build. Outgoing packets are seen in both builds. I'm not sending any packets in this program.
I'm building with VS2008 native C++ under Win7 x64.
My issue was with the firewall. When the project was created in VS it apparently put an "Allow" entry in the firewall for network access by the project build, but only for the debug build of the program.
I had to add another entry for the release build and this then allowed incoming packets. The advance firewall settings under Win7 can also cause specific protocols to be blocked, so if you're getting only partial incoming messages check those settings for your program's entry.

Today I was wondering how to do the exact same thing! Here is my code which now seems to work, credit for getting this working is due to fellow answerer 'Tom Erik' for suggesting ProtocolType.IP.
static void Main(string[] args)
{
// Receive some arbitrary incoming IP traffic to an IPV4 address on your network adapter using the raw socket - requires admin privileges
Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.IP);
IPAddress ipAddress = Dns.GetHostEntry(Dns.GetHostName()).AddressList
.Where((addr) => addr.AddressFamily == AddressFamily.InterNetwork)
.Where((addr) => addr.GetAddressBytes()[0] != 127)
.First();
s.Bind(new IPEndPoint(ipAddress, 0));
byte[] b = new byte[2000];
EndPoint sender = new IPEndPoint(0, 0);
int nr = s.ReceiveFrom(b, SocketFlags.None, ref sender);
}

DNS relay UDP on port 53

I noticed that BT Home are sending back fake DNS results from their DNS servers and this allows sites to bypass the IP addresses i have blocked in the firewall so i was looking to create my own DNS relay/server.
So far i can receive request on UDP port 53 and send them off to the DNS server and get a valid byte[] stream result and i then send back to the browser using the remote client port the request was made on but the browser just sends the request back again.
I've tested the code from a socket and the results work OK but for some reason IE/FF simply will not except the results.
public void Listen()
{
receiveSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp );
receiveEndPoint = new IPEndPoint(IPAddress.Any, receivePort); receiveSocket.Bind(receiveEndPoint);
receivePort = (receiveSocket.LocalEndPoint as IPEndPoint).Port;
receiveBuffer = new byte[BufferSize];
receiveAsyncResult = receiveSocket.BeginReceiveFrom(receiveBuffer, 0, receiveBuffer.Length, SocketFlags.None, ref receiveEndPoint, new AsyncCallback(NetworkMessageReceivedCallback), receiveSocket);
}
public void NetworkMessageReceivedCallback(IAsyncResult asyncResult)
{
EndPoint remoteEndPoint = null;
byte[] bytes = null;
remoteEndPoint = new IPEndPoint(IPAddress.Any, 0); //Will contain the clients port
int bytesRead = receiveSocket.EndReceiveFrom(asyncResult, ref remoteEndPoint);
bytes = new Byte[bytesRead];
Buffer.BlockCopy(receiveBuffer, 0, bytes, 0, bytesRead);
//string ip = "208.67.222.222";
string ip = "192.168.1.254";
IPAddress dnsServer = IPAddress.Parse(ip);
Response R = Resolver.Lookup(bytes, dnsServer);
receiveSocket.SendTo(R.Message , remoteEndPoint);//127.0.0.1
receiveSocket.Close();
Listen();
}

I never dealt with raw DNS from C# but it looks like you are trying to resolve the bytes you received from the client, instead of just relaying them to the DNS server.
The message you read off the UDP socket contains a DNS query, not just a host name. Take a look at the RFC 2929 for what goes in there.
You might be interested in this little but great DNS filter - adsuck - by Marco Peereboom (though it's for Unix, not Windows).

Also, shouldn't your try and listen to UDP and TCP. I think UDP is used mostly for authoritative DNS queries.