Get MAC address via TCPListener in C#

Question

Is it possible to get MAC Address of remote client via TCPListener in C#?

using System;  
using System.Net;  
using System.Net.Sockets;  
using System.IO;  
using System.Text;  

namespace TCPserver  
{  
    class Program  
    {  
        private const int BUFSIZE = 32;  

        static void Main(string[] args)  
        {  
            if (args.Length > 1) // Test for correct of args  
                throw new ArgumentException("Parameters: [<Port>]");  

            int servPort = (args.Length == 1) ? Int32.Parse(args[0]) : 7;  

            TcpListener listener = null;  

            try  
            {  
                // Create a TCPListener to accept client connections  
                listener = new TcpListener(IPAddress.Any, servPort);  
                listener.Start();  
            }  
            catch (SocketException se)  
            {  
                Console.WriteLine(se.Message);  
                Environment.Exit(se.ErrorCode);  
            }  

            byte[] rcvBuffer = new byte[BUFSIZE]; // Receive buffer  
            int bytesRcvd; // Received byte count  

            for (; ; )  
            { // Run forever, accepting and servicing connections  

                TcpClient client = null;  
                NetworkStream ns = null;  
                try  
                {  
                    client = listener.AcceptTcpClient(); // Get client connection  
                    ns = client.GetStream();  
                    Console.Write("Handling client - ");  

                    // Receive until client closes connection  
                    int totalBytesEchoed = 0;  
                    while ((bytesRcvd = ns.Read(rcvBuffer, 0, rcvBuffer.Length)) > 0)  
                    {  
                        ns.Write(rcvBuffer, 0, bytesRcvd);  
                        totalBytesEchoed += bytesRcvd;  
                    }  
                    Console.WriteLine("echoed {0} bytes.", totalBytesEchoed);  

                    ns.Close();  
                    client.Close();  

                }  
                catch (Exception e)  
                {  
                    Console.WriteLine(e.Message);  
                    ns.Close();  
                }  
            }  
        }  
    }  
}  

Answer 1

So the answer is no it is impossible.

But by IP address we can get MAC address like this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication14
{
    class Program
    {
        static void Main(string[] args)
        {
            IPAddress address = IPAddress.Parse("12.3.0.42");
            byte[] t = GetMacAddress(address);
            string mac = string.Join(":", (from z in t select z.ToString("X2")).ToArray());
            Console.WriteLine(mac);
            Console.ReadLine();
        }

        [DllImport("iphlpapi.dll", ExactSpelling = true)]
        public static extern int SendARP(uint destIP, uint srcIP, byte[] macAddress, ref uint macAddressLength);

        public static byte[] GetMacAddress(IPAddress address)
        {
            byte[] mac = new byte[6];
            uint len = (uint)mac.Length;
            byte[] addressBytes = address.GetAddressBytes();
            uint dest = ((uint)addressBytes[3] << 24)
              + ((uint)addressBytes[2] << 16)
              + ((uint)addressBytes[1] << 8)
              + ((uint)addressBytes[0]);
            if (SendARP(dest, 0, mac, ref len) != 0)
            {
                throw new Exception("The ARP request failed.");
            }
            return mac;
        }
    }
}

Answer 2

No. The MAC address is part of the Link layer, only used to communicate two hosts in the same physical link.

Oversimplifying..., imagine that a and c are computers, and b is a router.

a <-> b <-> c

If a wants to send a packet to c, it has to go through b. So a sends packet with source IP address a, target IP address c, source MAC address a and target MAC address b, since the router is the next hop. Then when b gets that packet, it will send it to c using source IP address a, target IP address c, source MAC address b and target MAC address c.