Help for designing a Firewall

class IpPacketFilter
{
    [DllImport("iphlpapi.dll", EntryPoint = "PfBindInterfaceToIPAddress")]
    public static extern int PfBindInterfaceToIPAddress(IntPtr Interface_handle, PFADDRESSTYPE pfatType, ref int ip_address);
      [DllImport("iphlpapi.dll", EntryPoint = "PfCreateInterface")]
    public static extern int PfCreateInterface(int dwName, PFFORWARD_ACTION inAction, PFFORWARD_ACTION outAction, bool UseLog, bool MustBeUnique, ref IntPtr ppInterface);
    //////    ////
    [DllImport("iphlpapi.dll", EntryPoint = "PfAddFiltersToInterface")]
    public static extern int PfAddFiltersToInterface(
        IntPtr interface_handle,
        int cInFilters,
        [MarshalAsAttribute(UnmanagedType.Struct)]
        ref PPF_FILTER_DESCRIPTOR pfiltIn,
        int cOutFilters,
        [MarshalAsAttribute(UnmanagedType.Struct)]
        ref PPF_FILTER_DESCRIPTOR pfiltOut,
        [MarshalAsAttribute(UnmanagedType.Struct)]
        ref PPF_FILTER_DESCRIPTOR pfHandle
        );
}
public unsafe struct PPF_FILTER_DESCRIPTOR
{
    public FILTER_FLAGS dwFilterFlags;
    public int dwRule;
    public PFADDRESSTYPE pfatType;
    public int* SrcAddr;
    public int* SrcMask;
    public int* DstAddr;
    public int* DstMask;
    public PROTOCOL dwProtocol;
    public int fLateBound;
    public int wSrcPort;
    public int wDstPort;
    public int wSrcPortHighRange;
    public int wDstPortHighRange;
}
public enum PFFORWARD_ACTION : int
{
    PF_ACTION_FORWARD = 0,
    PF_ACTION_DROP
}
public enum PFADDRESSTYPE : int
{
    PF_IPV4,
    PF_IPV6
}
public  enum PROTOCOL : int
{
    ANY = 0x00,
    ICMP = 0x01,
    TCP = 0x06,
    UDP = 0x11
}
public  enum FILTER_FLAGS : int
{
    FD_FLAGS = 0x1
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Net;
 
namespace ConsoleApplication1
{
    
    class Program
    {
        internal const int FALSE = 0;
        internal const int TRUE = 1;
        static void Main(string[] args)
        {
            string[] hostsToBlock = new string[2]; 
            hostsToBlock[0] = "192.168.0.2,255.255.255.0,0";  
            //blocks all traffic on any port to/from 67.77.87.97   
            hostsToBlock[1] = "0.0.0.0,0.0.0.0,29000";   
            //blocks all traffic on port 29000, in and out   
            StartPacketFilter(hostsToBlock);
            Console.ReadLine();
           
         }
        internal static int lIpFromString(string sIpAddress) 
        { 
            int lIp = 0;
            try 
            {
                string[] octets = sIpAddress.Split(new string[] { "." }, StringSplitOptions.None);
                if (octets.Length != 4)   
                    return 0;
                for (int i = 0; i < 4; i++)   
                    lIp |= (int.Parse(octets[i]) << (i * 8));
            } 
            catch 
            { 
            }
            return lIp;
        }
        internal static string[] GetLocalIpAddresses()
        {
            IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
            string[] localIpAddresses = new string[host.AddressList.Length];
            for (int i = 0; i < host.AddressList.Length; i++) 
            { 
                localIpAddresses[i] = host.AddressList[i].ToString();
            }
                 return localIpAddresses; 
        }
        internal static bool StartPacketFilter(string[] hosts)
        {  
            string[] localIpAddresses = GetLocalIpAddresses();
            //Console.WriteLine(localIpAddresses);
            if (localIpAddresses == null)
                return false; 
            foreach (string localAddress in localIpAddresses)
            {
               
                int result; 
                IntPtr interfaceHandle = new IntPtr();   
                //convert the string IP to an unsigned int for p/invoke
                int lLocalIp = lIpFromString(localAddress);
                 //create a filter interface in the tcp/ip stack 
                result = IpPacketFilter.PfCreateInterface(0, PFFORWARD_ACTION.PF_ACTION_FORWARD, PFFORWARD_ACTION.PF_ACTION_FORWARD, false, true, ref interfaceHandle);
                if (result != 0)
                    return false; 
                //bind interface to an ip address 
                result = IpPacketFilter.PfBindInterfaceToIPAddress(interfaceHandle, PFADDRESSTYPE.PF_IPV4, ref lLocalIp);    
                if (result != 0)
                    return false; 
                foreach (string targetHost in hosts)   
                {        
                    ////IntPtr filterHandle = new IntPtr();  
                    string[] hostDetail = targetHost.Split(new string[] { "," }, StringSplitOptions.None);
                   
                    if (hostDetail != null && hostDetail.Length == 3)  
                    {       
                        //build the filter structure  
                        PPF_FILTER_DESCRIPTOR filter = new PPF_FILTER_DESCRIPTOR();   
                        filter.dwFilterFlags = FILTER_FLAGS.FD_FLAGS; 
                        filter.dwRule = FALSE;             
                        filter.pfatType = PFADDRESSTYPE.PF_IPV4;     
                        filter.dwProtocol = PROTOCOL.TCP;        
                        int iSrcAddr = lLocalIp;              
                        int iSrcMask = lIpFromString("255.255.255.0");
                        filter.wSrcPort = 0;  
                        filter.wSrcPortHighRange = 0;         
                        int iDstAddr = lIpFromString(hostDetail[0]);    
                        int iDstMask = lIpFromString(hostDetail[1]); 
                        filter.wDstPort = int.Parse(hostDetail[2]);       
                        filter.wDstPortHighRange = int.Parse(hostDetail[2]); 
 
                        unsafe          
                        {         
                            filter.SrcAddr = &iSrcAddr;   
                            filter.DstAddr = &iDstAddr;    
                            filter.SrcMask = &iSrcMask; 
                            filter.DstMask = &iDstMask;  
                        }             
                        // add filter to interface (both inbound and outbound)   
                        result = IpPacketFilter.PfAddFiltersToInterface(interfaceHandle, 1, ref filter, 1, ref filter, ref filter);
                        
                        if (result != 0) 
                            return false;
                        
                    }
                  
                }
                
            }
           
            return true;
        }
    }
}