C# raw socket ARP reply

Question

I am a student trying to learn more about the ARP and sockets in C#

To do this I am trying to send ARP requests and replies using a raw Socket in C#.

I have manually reconstructed an ARP reply in an byte array and I am trying to send it using the Socket.Send method.

static void Main(string[] args)
{
    // Create a raw socket
    var socket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Raw);

    // Setup ARP headers
    byte[] buffer = new byte[]
    {
        0x34, 0x97, 0xf6, 0x22, 0x04, 0xe8, // Ethernet Destination mac
        0x70, 0x1c, 0xe7, 0x51, 0x94, 0x0b, // Ethernet source mac
        0x08, 0x06,                         // Type: ARP
        00, 0x01,                           // Hardware type: Ethernet
        0x08, 0x00,                         // Protocol type: IPv4
        0x06,                               // Hardware size: 6
        0x04,                               // Protocol size: 4
        00, 0x02,                           // Opcode: Reply
        0x70, 0x1c, 0xe7, 0x51, 0x94, 0x0b, // Sender mac addr
        0xc0, 0xa8, 0x01, 0x34,             // Sender IP addr 192.168.1.52
        0x34, 0x97, 0xf6, 0x22, 0x04, 0xe8, // Target mac addr
        0xc0, 0xa8, 0x01, 0x01              // Target ip addr 192.168.1.1
    };

    // Send ARP reply
    socket.Send(buffer, buffer.Length, SocketFlags.None);

    Console.ReadKey();
}

When I try to run this code, the application throws a SocketException:

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

Tho, to my understanding, I have supplied the destination MAC address in the request.

How should I correctly send an ARP reply(/request) using a Socket?

PS: I know there is probably a library for this, but I think I won't learn much about sockets and ARP when using a library.

You can try to send to target broadcast ip (something like `socket.SendTo(buffer, buffer.Length, SocketFlags.None, new IPEndPoint(IPAddress.Parse("192.168.1.255"), 0));`, but I'm not sure it will do what you want (though it should remove exception). — Evk, Apr 02 '18 at 11:40

score 5 · Accepted Answer · answered May 17 '18 at 16:51

After a while I'd forgotten about this question but got the answer from an article my teacher showed me about Raw Sockets in a WinSock annex on MSDN.

One section of this article is particular interesting regarding the question:

Limitations on Raw Sockets

On Windows 7, Windows Vista, Windows XP with Service Pack 2 (SP2), and Windows XP with Service Pack 3 (SP3), the ability to send traffic over raw sockets has been restricted in several ways:

TCP data cannot be sent over raw sockets.
UDP datagrams with an invalid source address cannot be sent over raw sockets. The IP source address for any outgoing UDP datagram must exist on a network interface or the datagram is dropped. This change was made to limit the ability of malicious code to create distributed denial-of-service attacks and limits the ability to send spoofed packets (TCP/IP packets with a forged source IP address).
A call to the bind function with a raw socket for the IPPROTO_TCP protocol is not allowed.

UDP datagrams with an invalid source address cannot be sent over raw sockets. The IP source address for any outgoing UDP datagram must exist on a network interface or the datagram is dropped. This change was made to limit the ability of malicious code to create distributed denial-of-service attacks and limits the ability to send spoofed packets (TCP/IP packets with a forged source IP address).

So the simple answer to this question is: Sending packets like this with plain C# .net Framework is not possible.

For anyone who does want to send packets using C#: You can use the sharppcap library.

C# raw socket ARP reply

1 Answers1