C#

typedef struct _RASENTRYNAME { 
  DWORD  dwSize; 
  TCHAR  szEntryName[RAS_MaxEntryName + 1]; 
#if (WINVER >= 0x500)
  DWORD dwFlags;
  TCHAR  szPhonebookPath[MAX_PATH + 1];
#endif
} RASENTRYNAME; 

[StructLayout(LayoutKind.Sequential)]
public class RASENTRYNAME 
{ 
	public int  dwSize; 
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst = (int)Max.MaxEntryName + 1)]
	public string  szEntryName; 
	public int dwFlags;
	[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256 + 1)]
	public string  szPhonebookPath;
}

[DllImport("rasapi32", EntryPoint = "RasEnumEntries", CharSet = CharSet.Ansi)]
public static extern int EnumEntries(object menull, System.Text.StringBuilder phonebookpath,[In, Out] IntPtr rasentry, ref int size, out int entries);

RASENTRYNAME rasentry = new RASENTRYNAME();
size = rasentry.dwSize = Marshal.SizeOf(typeof(RASENTRYNAME));
size *= 10; //this is dumb, but we have to "guess" buffer size or specify enough size, same below
IntPtr prasentry = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(RASENTRYNAME)) * 10);
first = prasentry;
Marshal.StructureToPtr(rasentry, prasentry, true);
result = RASWrapper.EnumEntries(null, null, prasentry, ref size, out numcon);
for (int i = 0; i < numcon; i++)
{
	Marshal.PtrToStructure(prasentry,rasentry); 
	prasentry = new IntPtr(prasentry.ToInt32() + Marshal.SizeOf(typeof(RASENTRYNAME)));
}
Marshal.FreeHGlobal(first);