How do I access ARP-protocol information through .NET?

Question

I try to figure out which devices are online and which are offline in our LAN.
I have seen many programs doing a kind of graphical network overview, presenting LAN IP and MAC addresses.

I would like to know if and how those (ARP?) information can be pulled from C#/.NET ?

Answer 1

If you know which devices are out there you can use the Ping Class. This will allow you to at least fill up the ARP table. You can always execute ARP -a and parse the output if you have to. Here is also a link that shows how to pinvoke to call GetIpNetTable. I have included examples below of Ping Class and how to access the ARP table using the GetIpNetTable.

This is an example for the Ping Class

using System; using System.Net; using System.Net.NetworkInformation; using System.Text;  namespace Examples.System.Net.NetworkInformation.PingTest {     public class PingExample     {         // args[0] can be an IPaddress or host name.         public static void Main (string[] args)         {             Ping pingSender = new Ping ();             PingOptions options = new PingOptions ();              // Use the default Ttl value which is 128,             // but change the fragmentation behavior.             options.DontFragment = true;              // Create a buffer of 32 bytes of data to be transmitted.             string data = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";             byte[] buffer = Encoding.ASCII.GetBytes (data);             int timeout = 120;             PingReply reply = pingSender.Send (args[0], timeout, buffer, options);             if (reply.Status == IPStatus.Success)             {                 Console.WriteLine ("Address: {0}", reply.Address.ToString ());                 Console.WriteLine ("RoundTrip time: {0}", reply.RoundtripTime);                 Console.WriteLine ("Time to live: {0}", reply.Options.Ttl);                 Console.WriteLine ("Don't fragment: {0}", reply.Options.DontFragment);                 Console.WriteLine ("Buffer size: {0}", reply.Buffer.Length);             }         }     } } 

This is an example of the GetIpNetTable.

using System; using System.Runtime.InteropServices; using System.ComponentModel;  using System.Net;  namespace GetIpNetTable {    class Program    {       // The max number of physical addresses.       const int MAXLEN_PHYSADDR = 8;        // Define the MIB_IPNETROW structure.       [StructLayout(LayoutKind.Sequential)]       struct MIB_IPNETROW       {          [MarshalAs(UnmanagedType.U4)]          public int dwIndex;          [MarshalAs(UnmanagedType.U4)]          public int dwPhysAddrLen;          [MarshalAs(UnmanagedType.U1)]          public byte mac0;          [MarshalAs(UnmanagedType.U1)]          public byte mac1;          [MarshalAs(UnmanagedType.U1)]          public byte mac2;          [MarshalAs(UnmanagedType.U1)]          public byte mac3;          [MarshalAs(UnmanagedType.U1)]          public byte mac4;          [MarshalAs(UnmanagedType.U1)]          public byte mac5;          [MarshalAs(UnmanagedType.U1)]          public byte mac6;          [MarshalAs(UnmanagedType.U1)]          public byte mac7;          [MarshalAs(UnmanagedType.U4)]          public int dwAddr;          [MarshalAs(UnmanagedType.U4)]          public int dwType;       }        // Declare the GetIpNetTable function.       [DllImport("IpHlpApi.dll")]       [return: MarshalAs(UnmanagedType.U4)]       static extern int GetIpNetTable(          IntPtr pIpNetTable,          [MarshalAs(UnmanagedType.U4)]          ref int pdwSize,          bool bOrder);        [DllImport("IpHlpApi.dll", SetLastError = true, CharSet = CharSet.Auto)]       internal static extern int FreeMibTable(IntPtr plpNetTable);        // The insufficient buffer error.       const int ERROR_INSUFFICIENT_BUFFER = 122;        static void Main(string[] args)       {          // The number of bytes needed.          int bytesNeeded = 0;           // The result from the API call.          int result = GetIpNetTable(IntPtr.Zero, ref bytesNeeded, false);           // Call the function, expecting an insufficient buffer.          if (result != ERROR_INSUFFICIENT_BUFFER)          {             // Throw an exception.             throw new Win32Exception(result);          }           // Allocate the memory, do it in a try/finally block, to ensure          // that it is released.          IntPtr buffer = IntPtr.Zero;           // Try/finally.          try          {             // Allocate the memory.             buffer = Marshal.AllocCoTaskMem(bytesNeeded);              // Make the call again. If it did not succeed, then             // raise an error.             result = GetIpNetTable(buffer, ref bytesNeeded, false);              // If the result is not 0 (no error), then throw an exception.             if (result != 0)             {                // Throw an exception.                throw new Win32Exception(result);             }              // Now we have the buffer, we have to marshal it. We can read             // the first 4 bytes to get the length of the buffer.             int entries = Marshal.ReadInt32(buffer);              // Increment the memory pointer by the size of the int.             IntPtr currentBuffer = new IntPtr(buffer.ToInt64() +                Marshal.SizeOf(typeof(int)));              // Allocate an array of entries.             MIB_IPNETROW[] table = new MIB_IPNETROW[entries];              // Cycle through the entries.             for (int index = 0; index < entries; index++)             {                // Call PtrToStructure, getting the structure information.                table[index] = (MIB_IPNETROW) Marshal.PtrToStructure(new                   IntPtr(currentBuffer.ToInt64() + (index *                   Marshal.SizeOf(typeof(MIB_IPNETROW)))), typeof(MIB_IPNETROW));             }              for (int index = 0; index < entries; index++)             {                MIB_IPNETROW row = table[index];                IPAddress ip=new IPAddress(BitConverter.GetBytes(row.dwAddr));                Console.Write("IP:"+ip.ToString()+"\t\tMAC:");                 Console.Write( row.mac0.ToString("X2") + '-');                Console.Write( row.mac1.ToString("X2") + '-');                Console.Write( row.mac2.ToString("X2") + '-');                Console.Write( row.mac3.ToString("X2") + '-');                Console.Write( row.mac4.ToString("X2") + '-');                Console.WriteLine( row.mac5.ToString("X2"));              }          }          finally          {             // Release the memory.             FreeMibTable(buffer);          }       }    } }