using System;

using System.Collections.Generic;

using System.Data;

using System.Linq;

using System.Net;

using System.Net.Sockets;

using System.Runtime.InteropServices;

​

namespace StackOverflow2

{

    internal class Program

    {

        private static string _fcaptureIp = "192.168.100.5";

        private static Socket _fmainSocket = null;

        private static int IpHeaderSize = 0;

        private static byte[] _headerBytes = null;

        static void Main(string[] args)

        {

​

            IpHeaderSize = Marshal.SizeOf(typeof(IpV4Header));

            _fmainSocket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.IP);

            _fmainSocket.Bind(new IPEndPoint(IPAddress.Parse(_fcaptureIp), 0));

            _fmainSocket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.HeaderIncluded, true);

            byte[] byTrue = new byte[4] { 1, 0,0,0};

            byte[] byOut = new byte[4] ;//{ 1, 1,1,1 };

            _fmainSocket.IOControl(IOControlCode.ReceiveAll, byTrue, byOut);

            recv();

        }

​

        private static void recv()

        {

            byte[] buff = new byte[3000];

            while (true)

            {

                int count = _fmainSocket.Receive(buff);

                var ipHeader = GetIpHeaderFromBytes(buff, 0, IpHeaderSize);

                if(ipHeader.ip_srcaddr!= ipHeader.ip_destaddr)

               Console.WriteLine($"From: { new IPAddress(ipHeader.ip_srcaddr)} To: { new IPAddress(ipHeader.ip_destaddr)}");

            }

        }

​

        private static IpV4Header GetIpHeaderFromBytes(byte[] bytes, int offset, int headerSize)

        {

            var tmp = new List<byte>();

            for (int i = offset; i < (offset + headerSize); i++)

            {

                tmp.Add(bytes[i]);

            }

            byte[] headerBytes = tmp.ToArray();

            GCHandle handle = GCHandle.Alloc(headerBytes, GCHandleType.Pinned);

            IpV4Header ret =

                (IpV4Header)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(IpV4Header));

            handle.Free();

            return ret;

        }

​

        [StructLayout(LayoutKind.Explicit)]

        public struct IpV4Header

        {

            [FieldOffset(0)]

            public byte ip_verlen;       

            [FieldOffset(1)]

            public byte ip_tos;                     

            [FieldOffset(2)]

            public ushort ip_totallength;   

            [FieldOffset(4)]

            public ushort ip_id;        

            [FieldOffset(6)]

            public ushort ip_offset;        

            [FieldOffset(8)]

            public byte ip_ttl;         

            [FieldOffset(9)]

            public byte ip_protocol;        

            [FieldOffset(10)]

            public ushort ip_checksum;      

            [FieldOffset(12)]

            public uint ip_srcaddr;         

            [FieldOffset(16)]

            public uint ip_destaddr;        

            [FieldOffset(20)]

            public uint ip_params;

        }

    }

}