using System;
using System.Net;
using System.Runtime.InteropServices;

namespace IpAddressTable
{
  class IpAddressTableClass
  {
    [DllImport("iphlpapi.dll")]
    public static extern int GetIpAddrTable(IntPtr pIpAddrTable, ref int pdwSize, bool bOrder);

    public struct MIB_IPADDRROW
    { public int    dwAddr;
      public int    dwIndex;
      public int    dwMask;
      public int    dwBCastAddr;
      public int    dwReasmSize;
      public short  unused1;
      public short  unused2;
    }

    [STAThread]
    static void Main(string[] args)
    {
      int     size=0;
      IntPtr  buff=IntPtr.Zero;
      // получить размер буфера для PMIB_IPADDRTABLE:
      GetIpAddrTable(IntPtr.Zero, ref size, false);
      try
      {
        buff=Marshal.AllocHGlobal(size);
        // получить массив MIB_IPADDRROW
        if(GetIpAddrTable(buff, ref size, false)==0 && size>=4)
        {
          int           num=Marshal.ReadInt32(buff);

          for(int k=0, ptr=(int)buff+4; k<num; k++, ptr+=Marshal.SizeOf(typeof(MIB_IPADDRROW)))
          {
            MIB_IPADDRROW row=(MIB_IPADDRROW)Marshal.PtrToStructure((IntPtr)ptr, typeof(MIB_IPADDRROW));

            IPAddress adr=new IPAddress((long)row.dwAddr),
                      msk=new IPAddress((long)row.dwMask);
            Console.WriteLine("IP {0} mask {1}", adr, msk);
          }
        }
      }
      finally
      {
        if(buff!=IntPtr.Zero) Marshal.FreeHGlobal(buff);
      }
    }
  }
}