This example will show how to create proxy-like server that will stand between application (client) and its remote server using asynchronous sockets.
Such a server gives ability to filter and/or inject packets during connection and should be invisible to the remote host. Example shows also how to use asynchronous socket functions and how to force client application to use local IP address.
The most important problem to solve before creating proxy server is to force client application to connect to our local interface instead of their default one. The easy way is to override destination IP address by setting it to the local interface (network adapter). This can be done with either active NIC (if there is more than 1 available because we still need one to communicate with the world) or virtual network adapter. The second approach works well.
To install Microsoft Loopback Adapter on Windows 7 (and Vista) open Device Manager (WinKey+Break -> Hardware -> Device Manager) and select any device then open Action menu and Add Legacy Hardware. Click Next, select manual installation from list, Next and select Network adapters. From the manufacturers list select Microsoft and then Microsoft Loopback Adapter. Click next few more times to finish installation.
For Windows XP open Control Panel and select Add Hardware. Click Next, select Yes, I have already connected the hardware. Next and scroll Installed hardware list to the bottom, Add a new hardware device, click Next. Select Install the hardware manually, click Next, choose Network adapters, Next, use Microsoft as Manufacturer and finally select Microsoft Loopback Adapter. Click Next few times to finish installation.
When virtual network adapter is installed desired IP address has to be set. This example uses google.com IP address. Open network connections and select local connection assigned to Microsoft Loopback Adapter (probably "Local connection 2" or 3). Then properties and TCP/IPv4 properties. Manually set IP address to 209.85.229.147. Leave gateway blank. Now you can test if settings are correct by simply write http://209.85.229.147/ address in any browser. Google.com page should not be available (to undo this turn off loopback adapter connection).
How proxy server works?
Picture above presents standard connection between client and server. Client application is using active network interface with some IP address set. During connection OS assigns port to created socket.
The second picture shows proxy server between client and remote server. Listener interface is hiding remote server's IP. When listener detects incoming connection proxy server will try to connect to the remote server using outgoing interface and then transmit any packets between client and server.
The code
Application has small configuration section:
public const int PACKET_BUFFSIZE = 2048; // packet buffer in bytes
private const string LOCAL_OUT_IPADDR = "192.168.1.100"; // active localhost external address (set yours)
private const string TARGET_IPADDR = "209.85.229.147"; // destination address (google.com)
private static readonly int[] TARGET_PORTS = new int[] {
80,
//8080
};
Remember to use your active IP as LOCAL_OUT_IPADDR. Since this example is using port 80 for local listener you have to temporary stop IIS server if you have it installed.
Buffer size is not so important because even if some data is larger than buffer capacity it will be divided to pieces and process as few packets.
Separate thread with listener is started for every port in TARGET_PORTS array (only one, port 80 in example):
private static void RunListener(IPAddress listenerInterface, IPAddress outgoingInterface, int listenerPort, int listNo)
{
TcpListener listener = new TcpListener(listenerInterface, listenerPort);
listeners.Add(listener);
listener.Start();
Console.WriteLine("listener {0} started at {1}:{2}", listNo, listenerInterface.ToString(), listenerPort);
while (true)
{
Console.WriteLine("listener {0} is waiting for a new client", listNo);
Socket incoming_socket = listener.AcceptSocket();
Console.WriteLine("listener {0}: client connected", listNo);
// connecting remote host
Console.WriteLine("listener {0} is connecting to remote host {1}:{2}", listNo, TARGET_IPADDR, listenerPort;
Socket remote_socket = ConnectSocket(new IPEndPoint(outgoingInterface, 0), TARGET_IPADDR, listenerPort);
if (remote_socket == null)
{
Console.WriteLine("listener {0}: outgoing connection failed", listNo);
continue;
}
Console.WriteLine("listener {0}: connected to remote host {1}:{2}", listNo, TARGET_IPADDR, listenerPort);
// begin receive on input
SocketStateObj iso = new SocketStateObj(incoming_socket, remote_socket);
sockets.Add(iso);
incoming_socket.BeginReceive(iso.buffer, 0, SocketStateObj.BUFF_SIZE, SocketFlags.None,
new AsyncCallback(Read_Callback), iso);
// begin receive on output
SocketStateObj oso = new SocketStateObj(remote_socket, incoming_socket);
sockets.Add(oso);
remote_socket.BeginReceive(oso.buffer, 0, SocketStateObj.BUFF_SIZE, SocketFlags.None,
new AsyncCallback(Read_Callback), oso);
}
}
The above code section responsibility is to wait for incoming connection (from client application), accept it and then connect to remote host from outgoing interface. When this is done both created sockets are set to receiving data in asynchronous mode.
Socket.BeginReceive() method has a few arguments from which the most important are AsyncCallback callback and object state. Callback is a delegate to function handling received data and state is an object passed to that function. It is good to create your own method used as state argument:
public class SocketStateObj
{
public static readonly int BUFF_SIZE = Program.PACKET_BUFFSIZE;
public Socket in_socket = null;
public Socket out_socket = null;
public byte[] buffer = new byte[BUFF_SIZE];
public SocketStateObj(Socket in_socket)
{
this.in_socket = in_socket;
}
public SocketStateObj(Socket in_socket, Socket out_socket)
{
this.in_socket = in_socket;
this.out_socket = out_socket;
}
}
Read_Callback() function from this example is responsible for handling packets data. It is retrieving SocketStateObj object from AsyncState object and finishing receive:
SocketStateObj so = (SocketStateObj)ar.AsyncState;
s1 = so.in_socket;
s2 = so.out_socket;
int count = s1.EndReceive(ar);
Socket s1 (input one) is then set again to receive and s2 (output) used to transmit data to destination:
s1.BeginReceive(so.buffer, 0, SocketStateObj.BUFF_SIZE, SocketFlags.None,
new AsyncCallback(Read_Callback), so);
s2.Send(tmpbuff, 0, count, SocketFlags.None);
Read_Callback() function here is also a place where packets can be filter, resend or inject (this is marked in attached code). In this example only packet information is retrieved and shown on console.
How to verify if example works?
If configuration steps are performed correctly and all necessary interfaces are present in system http://209.85.229.147/ address is active in browser, google.com is available and application window will looks like in following screen:
Of course google.com address and a browser as a client application was only for this example purpose. Almost any application can be used if we want to monitor it or automate some tasks.
For debugging you can use Wireshark packet analyzer (http://www.wireshark.org/ ) to check if all packets are correctly transmit and some of built in Windows commands like ipconfig, netstat -n and netstat -a.
See attached code sample for complete solution.
Damian KozlowskiPosted May 17, 2017, 4:42 AM
It dosent work for me. I take connection timeout
javad sadeghiPosted Jan 1, 2015, 10:22 PM
[email protected]
javad sadeghiPosted Jan 1, 2015, 10:05 PM
http://www.codeproject.com/Questions/857367/Get-all-network-packets-from-one-network-card-and
javad sadeghiPosted Jan 1, 2015, 10:03 PM
private Socket mainSocket; private byte[] byteData = new byte[4096]; private bool bContinueCapturing = false; private delegate void AddTreeNode(TreeNode node); public Form1() { InitializeComponent(); } private void Form1_Load(object sender, EventArgs e) { string strIP = null; IPHostEntry HosyEntry = Dns.GetHostEntry((Dns.GetHostName())); if (HosyEntry.AddressList.Length > 0) { foreach (IPAddress ip in HosyEntry.AddressList) { strIP = ip.ToString(); cmbInterfaces.Items.Add(strIP); } } } private void Form1_FormClosing(object sender, FormClosingEventArgs e) { if (bContinueCapturing) { mainSocket.Close(); } } private void btnStart_Click(object sender, EventArgs e) { if (cmbInterfaces.Text == "") { MessageBox.Show("Select an Interface to capture the packets.", "sniffer", MessageBoxButtons.OK, MessageBoxIcon.Error); return; } try { if (!bContinueCapturing) { btnStart.Text = "&Stop"; bContinueCapturing = true; mainSocket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.IP); mainSocket.Bind(new IPEndPoint(IPAddress.Parse(cmbInterfaces.Text), 0)); mainSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.HeaderIncluded, true); byte[] byTrue = new byte[4] { 1, 0, 0, 0 }; byte[] byOut = new byte[4] { 1, 0, 0, 0 }; mainSocket.IOControl(IOControlCode.ReceiveAll, byTrue, byOut); mainSocket.Receive(byteData); mainSocket.BeginReceive(byteData, 0, byteData.Length, SocketFlags.None, new AsyncCallback(OnReceive), null); } else { btnStart.Text = "&Start"; bContinueCapturing = false; mainSocket.Close(); } } catch (Exception ex) { MessageBox.Show(ex.Message, "sniffer", MessageBoxButtons.OK, MessageBoxIcon.Error); } } private void OnReceive(IAsyncResult ar) { try { int nReceived = mainSocket.EndReceive(ar); if (bContinueCapturing) { byteData = new byte[4096]; mainSocket.BeginReceive(byteData, 0, byteData.Length, SocketFlags.None, new AsyncCallback(OnReceive), null); } } catch (ObjectDisposedException) { } catch (Exception ex) { MessageBox.Show(ex.Message, "sniffer", MessageBoxButtons.OK, MessageBoxIcon.Error); } } }
javad sadeghiPosted Jan 1, 2015, 10:02 PM
Get all network packets from one network card and send it to the second network card?Hi I have two network cards on your system. I want to write a program in C#. The first network card receive the packets and sends them to a second network card. I have written a program that receives the first packet network card.I have written a program code: I want to write a program that sends packets received a second network card. Please help me.
jon henryPosted Dec 19, 2011, 4:15 PM
Sorry for the double post. I like the concept, I wish I could get it to work. I setup the loopback adapter, pasted in the code, edited the outgoing IP addreess and the code seem to run without error - but the browser window gives the "Problem Loading Page" error. Here's (part of) what goes to the console: PACKET_BUFFSIZE = 2048 LOCAL_OUT_IPADDR = 192.168.6.110 TARGET_IPADDR = 209.85.229.147 TARGET_PORTS: 80 local active IP4 interfaces: 0: 209.85.229.147 1: 192.168.6.110 target interface address set to 209.85.229.147 local outgoing interface address set to 192.168.6.110 --ok-- ANY KEY TO STOP AND CLOSE ALL listener 0 started at 209.85.229.147:80 listener 0 is waiting for a new client listener 0: client connected listener 0 is connecting to remote host 209.85.229.147:80 listener 0: connected to remote host 209.85.229.147:80 listener 0 is waiting for a new client listener 0: client connected [15:46:32] packet 0 -> S: 192.168.6.110:3959 D: 209.85.229.147:80 len: 475 listener 0 is connecting to remote host 209.85.229.147:80 listener 0: connected to remote host 209.85.229.147:80 listener 0 is waiting for a new client listener 0: client connected [15:46:33] packet 1 -> S: 192.168.6.110:3960 D: 209.85.229.147:80 len: 475 listener 0 is connecting to remote host 209.85.229.147:80 listener 0: connected to remote host 209.85.229.147:80 listener 0 is waiting for a new client [15:46:34] packet 2 -> S: 192.168.6.110:3961 D: 209.85.229.147:80 len: 475 And over and over it goes. It's as if the packet sent by the remote_socket does not go to the external host, but is intercepted by the loopback interface. And that me to this question. What is it about the remote_socket that will allow it not to be intercepted by the loopback adapter?? How is it any different than the browser client?? Note: I am running Windows XP. Thanks in advance.
jon henryPosted Dec 19, 2011, 4:01 PM
Test