Question

I have a following problem. I created a PInvoke in a Windows CE .NET managed project for GetIpForwardTable function. When I call the function in returns the result, but the results are different from the result returned by the route command. There are more entries in the table, Mask and Destination changed places and NextHop is always set to 0.0.0.0

Here is the class (one needs to call IPForwardEntry.GetIpForwardTable()).

public class IPForwardEntry
{
    public enum ForwardType
    {
        Other = 1,
        Invalid = 2,
        Direct = 3,
        Indirect = 4
    }

    public enum ForwardProtocol
    {
        Other = 1,
        Local = 2,
        NetMGMT = 3,
        ICMP = 4,
        EGP = 5,
        GGP = 6,
        Hello = 7,
        RIP = 8,
        IS_IS = 9,
        ES_IS = 10,
        CISCO = 11,
        BBN = 12,
        OSPF = 13,
        BGP = 14,
        NT_AUTOSTATIC = 10002,
        NT_STATIC = 10006,
        NT_STATIC_NON_DOD = 10007
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_IPFORWARDROW
    {
        public uint dwForwardDest;
        public uint dwForwardMask;
        public int dwForwardPolicy;
        public uint dwForwardNextHop;
        public int dwForwardIfIndex;
        public ForwardType dwForwardType;
        public ForwardProtocol dwForwardProto;
        public int dwForwardAge;
        public int dwForwardNextHopAS;
        public int dwForwardMetric1;
        public int dwForwardMetric2;
        public int dwForwardMetric3;
        public int dwForwardMetric4;
        public int dwForwardMetric5;
    }

    private IPForwardEntry(MIB_IPFORWARDROW forwardRow)
    {
        myForwardRow = forwardRow;
    }

    private MIB_IPFORWARDROW myForwardRow;

    private const int NO_ERROR = 0;

    [DllImport("Iphlpapi.dll")]
    private static extern int CreateIpForwardEntry(MIB_IPFORWARDROW[] pRoute);

    [DllImport("Iphlpapi.dll")]
    private static extern int GetIpForwardTable(MIB_IPFORWARDROW[] pIpForwardTable, ref long pdwSize, bool bOrder);

    public static IPForwardEntry[] GetIpForwardTable()
    {
        long tableSize = 0;
        GetIpForwardTable(null, ref tableSize, true);

        MIB_IPFORWARDROW[] forwardTable = new MIB_IPFORWARDROW[tableSize / Marshal.SizeOf(typeof(MIB_IPFORWARDROW)) + 1];

        long tableSizeOld = tableSize;

        if (GetIpForwardTable(forwardTable, ref tableSize, false) != NO_ERROR)
            throw new SystemException();

        if (tableSizeOld != tableSize)
            throw new SystemException();


        IPForwardEntry[] result = new IPForwardEntry[forwardTable.Length];

        for (int i = 0; i < forwardTable.Length; i++)
            result[i] = new IPForwardEntry(forwardTable[i]);

        return result;

    }

    #region members

    public IPAddress FordwardDestination
    {
        get
        {
            return new IPAddress(myForwardRow.dwForwardDest);
        }
        set
        {
            myForwardRow.dwForwardDest = (uint) value.Address;
        }
    }

    public IPAddress ForwardMask
    {
        get
        {
            return new IPAddress(myForwardRow.dwForwardMask);
        }
        set
        {
            myForwardRow.dwForwardMask = (uint) value.Address;
        }
    }

    public int ForwardPolicy
    {
        get
        {
            return myForwardRow.dwForwardPolicy;
        }
        set
        {
            myForwardRow.dwForwardPolicy = value;
        }
    }

    public IPAddress ForwardNextHop
    {
        get
        {
            return new IPAddress(myForwardRow.dwForwardNextHop);
        }
        set
        {
            myForwardRow.dwForwardNextHop = (uint) value.Address;
        }
    }

    public int ForwardInterfaceIndex
    {
        get
        {
            return myForwardRow.dwForwardIfIndex;
        }
        set
        {
            myForwardRow.dwForwardIfIndex = value;
        }
    }


    public ForwardType ForwrdType
    {
        get
        {
            return myForwardRow.dwForwardType;
        }
        set
        {
            myForwardRow.dwForwardType = value;
        }
    }

    public ForwardProtocol Protocol
    {
        get
        {
            return myForwardRow.dwForwardProto;
        }
        set
        {
            myForwardRow.dwForwardProto = value;
        }
    }


    public int ForwardAge
    {
        get
        {
            return myForwardRow.dwForwardAge;
        }
        set
        {
            myForwardRow.dwForwardAge = value;
        }
    }

    public int ForwardNextHopAS
    {
        get
        {
            return myForwardRow.dwForwardNextHopAS;
        }
        set
        {
            myForwardRow.dwForwardNextHopAS = value;
        }
    }

    public int ForwardMetric1
    {
        get
        {
            return myForwardRow.dwForwardMetric1;
        }
        set
        {
            myForwardRow.dwForwardMetric1 = value;
        }
    }

    public int ForwardMetric2
    {
        get
        {
            return myForwardRow.dwForwardMetric2;
        }
        set
        {
            myForwardRow.dwForwardMetric2 = value;
        }
    }

    public int ForwardMetric3
    {
        get
        {
            return myForwardRow.dwForwardMetric3;
        }
        set
        {
            myForwardRow.dwForwardMetric3 = value;
        }
    }

    public int ForwardMetric4
    {
        get
        {
            return myForwardRow.dwForwardMetric4;
        }
        set
        {
            myForwardRow.dwForwardMetric4 = value;
        }
    }

    public int ForwardMetric5
    {
        get
        {
            return myForwardRow.dwForwardMetric5;
        }
        set
        {
            myForwardRow.dwForwardMetric5 = value;
        }
    }

    #endregion

}

Answer 1

GetIpForwardTable doesn’t return an array of MIB_IPFORWARDROW objects, it returns a MIB_IPFORWARDTABLE, that contains an array of rows and the number. So that’s at least one issue. There are likely others as this is not a straightforward P/Invoke set for marshaling.

For what it’s worth, I’ve already implemented all of this code in the Smart Device Framework, specifically in the OpenNETCF.Net.NetworkInformation.IPRoutingTable class