Delete ARP entry on Windows CE 6.0 CF.NET 2.0

Question

the task I had to solve was to send an ARP request to a target device.

So I started to P/Invoke SendARP in C# - CompactFramework.NET 2.0 for Windows CE 6.0.

[DllImport("iphlpapi.dll")]
private static extern int SendARP(uint destIp, uint srcIp, [Out] byte[] pMacAddr, ref int phyAddrLen);

After recognising that the local ARP cache is used in case of an already existing entry of the requested IP I wanted to delete this entry manually.

So I started to acquire the IPNetTable by using the following code from https://stackoverflow.com/a/1148861/3635715

I ended up to load my MIB_IPNETROW successfully, but when I call

[DllImport("iphlpapi.dll")]
private static extern int DeleteIpNetEntry(MIB_IPNETROW pArpEntry);

I get an ERROR_INVALID_PARAMETER exception (code 87).

This is my struct: (I tested two versions of it)

[StructLayout(LayoutKind.Sequential)]
internal 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;
}

//[StructLayout(LayoutKind.Sequential)]
//internal struct MIB_IPNETROW
//{
//    [MarshalAs(UnmanagedType.U4)] public int dwIndex;
//    [MarshalAs(UnmanagedType.U4)] public int dwPhysAddrLen;
//    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] public byte[] bPhysAddr;
//    [MarshalAs(UnmanagedType.U4)] public int dwAddr;
//    [MarshalAs(UnmanagedType.U4)] public int dwType;
//}

And last but not least my function:

    private static void DeleteArpCache(string dstAddress, bool flush)
    {
        if (!string.IsNullOrEmpty(dstAddress))
        {
            IPAddress ipAddress = IPAddress.Parse(dstAddress);
            byte[] destination = ipAddress.GetAddressBytes();

            Log.DebugFormat("Try to get MIB_IPNETROW for IP [{0}]", dstAddress);
            MIB_IPNETROW? rowValue = GetRowByIpNetTable(destination);
            if (rowValue != null)
            {
                MIB_IPNETROW row = (MIB_IPNETROW) rowValue;

                if (flush)
                {
                    Log.DebugFormat("Try to delete ARP entries for Adapter Index {0}", row.dwIndex);
                    int result = FlushIpNetTable(row.dwIndex);
                    if (result == 0)
                    {
                        Log.Info("Deleted ARP entries successfully");
                    }
                    else
                    {
                        Log.ErrorFormat("Delete ARP entries failed with Code {0} for destination [{1}]", result,
                            dstAddress);
                    }
                }
                else
                {
                    Log.DebugFormat("Try to delete single ARP entry for IP [{0}]", dstAddress);
                    int result = DeleteIpNetEntry(row);
                    if (result == 0)
                    {
                        Log.Info("Deleted ARP entry successfully");
                    }
                    else
                    {
                        Log.ErrorFormat("Delete ARP entry failed with Code {0} for destination [{1}]", result,
                            dstAddress);
                    }
                }
            }
        }
    }

FlushIpNetTable works like a charm! So what could be the reason of my parameter mismatch at DeleteIpNetEntry? Has someone had a similar problem?

Kind regards!

Answer 1

Indeed! josef is right, this param is ref ...

[DllImport("iphlpapi.dll")]
private static extern int DeleteIpNetEntry(ref MIB_IPNETROW pArpEntry);

Thank you so much!