pinvoke.net: Edit: iphlpapi.PfAddFiltersToInterface

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Summary: The PfAddFiltersToInterface function adds the specified filters to the specified interface.

!!!!C# Signature:
    [DllImport("Iphlpapi.dll", EntryPoint = "PfAddFiltersToInterface")]
    internal static extern UInt32 PfAddFiltersToInterface(IntPtr ih, UInt32 cInFilters, 
        [MarshalAsAttribute(UnmanagedType.Struct)] ref PPF_FILTER_DESCRIPTOR pfiltIn, UInt32 cOutFilters, 
        [MarshalAsAttribute(UnmanagedType.Struct)] ref PPF_FILTER_DESCRIPTOR pFiltOut, IntPtr pfHandle);
!!!!VB Signature:
 Declare Function PfAddFiltersToInterface Lib "iphlpapi.dll" (TODO) As TODO
!!!!User-Defined Types:
        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        internal unsafe struct PPF_FILTER_DESCRIPTOR
        {
            public FILTER_FLAGS dwFilterFlags;
            public UInt32 dwRule;
            public PFADDRESSTYPE pfatType;

public UInt32* SrcAddr;
            public UInt32* SrcMask;
            public UInt32* DstAddr;
            public UInt32* DstMask;

public PROTOCOL dwProtocol;
            public UInt32 fLateBound;
            public UInt16 wSrcPort;
            public UInt16 wDstPort;
            public UInt16 wSrcPortHighRange;
            public UInt16 wDstPortHighRange;
        }

!!!!Notes:
    /// <summary>
    /// The PfAddFiltersToInterface function adds the specified filters to the specified interface.
    /// If the function succeeds, the return value is NO_ERROR.
    /// </summary>
    /// <param name="ih">[in] Specifies a handle to the interface.</param>
    /// <param name="cInFilters">[in] Specifies the number of input filter descriptions pointed to by the pfiltIn parameter.</param>
    /// <param name="pfiltIn">[in] Pointer to an array of filter descriptions to use as input filters.</param>
    /// <param name="cOutFilters">[in] Specifies the number of output filter descriptions pointed to by the pfiltOut parameter.</param>
    /// <param name="pFiltOut">[in] Pointer to an array of filter descriptions to use as output filters.</param>
    /// <param name="pfHandle">[out] Pointer to a buffer that receives an array of filter handles. If the caller does not require the filter handles, the caller may set this parameter to NULL.</param>
    /// <returns>If the function succeeds, the return value is NO_ERROR.</returns>

!!!!Sample Code:
    using System;
    using System.Collections.Generic;
    using System.Net;
    using System.Runtime.InteropServices;
    using Microsoft.Win32;

/// <summary>
    /// IP packet filter management wrapper for Iphlpapi.dll (Win 2000/XP)
    /// </summary>
    class Program
    {
        // C conversions for Fltdefs.h
        internal const int FALSE = 0;
        internal const int TRUE = 1;
        
        //enums
        internal enum PFFORWARD_ACTION : uint
        {
            PF_ACTION_FORWARD = 0,
            PF_ACTION_DROP
        }

internal enum PFADDRESSTYPE : uint
        {
            PF_IPV4,
            PF_IPV6
        }

internal enum PROTOCOL : uint
        {
            ANY = 0x00,
            ICMP = 0x01,
            TCP = 0x06,
            UDP = 0x11
        }

internal enum FILTER_FLAGS : uint
        {
            FD_FLAGS = 0x1
        }

[StructLayout(LayoutKind.Sequential, Pack = 1)]
        internal unsafe struct PPF_FILTER_DESCRIPTOR
        {
            public FILTER_FLAGS dwFilterFlags;
            public UInt32 dwRule;
            public PFADDRESSTYPE pfatType;

public UInt32* SrcAddr;
            public UInt32* SrcMask;
            public UInt32* DstAddr;
            public UInt32* DstMask;

static void Main(string[] args)
        {
            string[] hostsToBlock = new string[2];
            hostsToBlock[0] = "67.77.87.97,255.255.255.255,0";    //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);
            System.Windows.Forms.Application.Run();
        }

internal static UInt32 lIpFromString(string sIpAddress)
        {
            UInt32 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 |= (UInt32.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();
            if (localIpAddresses == null)
                return false;

foreach (string localAddress in localIpAddresses)
            {
                uint result;
                IntPtr interfaceHandle = new IntPtr();

//convert the string IP to an unsigned int for p/invoke
                UInt32 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;

uint iSrcAddr = lLocalIp;
                        uint iSrcMask = lIpFromString("255.255.255.255");
                        filter.wSrcPort = 0;
                        filter.wSrcPortHighRange = 0;

uint iDstAddr = lIpFromString(hostDetail[0]);
                        uint iDstMask = lIpFromString(hostDetail[1]);
                        filter.wDstPort = UInt16.Parse(hostDetail[2]);
                        filter.wDstPortHighRange = UInt16.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, filterHandle);
                        if (result != 0)
                            return false;
                    }
                }
            }
            return true;
        }
    }

Documentation: PfAddFiltersToInterface@msdn on MSDN