Windows Packet Filter

Windows Packet Filter (WinpkFilter) is a high-performance packet filtering framework for Windows that allows developers to transparently filter (view and modify) raw network packets at the NDIS level of the network stack with minimal impact on network activity and without having to write any low-level driver code.

Windows Packet Filter includes NDIS 3.1/4 hooking VxD driver (Windows 95/ME), NDIS 4 hooking filter driver (Windows NT/2000/XP), NDIS 5 Intermediate (Windows XP/2003) and NDIS 6 Lightweight Filter (LWF) drivers as well as companion user-mode API DLL and samples.

A key advantage of Windows Packet Filter in comparison to other packets filtering frameworks for Windows (based on Windows Filtering Platform (WFP) callout drivers, Layered Service Providers (LSP), TDI filters etc…) is the ability to manipulate raw Ethernet frames achieved by installing driver below all network protocol drivers and just above network interface driver. Thus, WinpkFilter driver has an ultimate control over all network traffic flow destined to or originated from your system and allows you to modify any packet, drop it or even forge and insert an entirely new one. Using Windows Packet Filter requires no experience in kernel mode programming on your behalf, since it provides you with a powerful user level API. However, if you need to implement your solution (to achieve better performance) in kernel mode, you can do that as well by adding your functional code directly to Windows Packet Filter driver’s code.

System Requirements

Windows 95/98/MillenniumWindows Server 2008*Windows Server 2012 R2
Windows NT 4.0Windows 7Windows 10
Windows 2000Windows Server 2008 R2Windows Server 2016
Windows XPWindows 8Windows Server 2019
Windows Server 2003Widows Server 2012Windows 11
Windows Vista*Windows 8.1Windows Server 2022

The following connections types are supported for the operating systems above:

  • Wired Ethernet (802.3)
  • Wi-Fi (802.11)
  • WAN (Analog/ISDN modems, PPPoE, 3G/4G mobile modems)
  • Mobile Broadband (PPIP)

Product features

  • Reliability and stability confirmed by hundreds of satisfied customers since product launch in 2002 ranged from small shareware companies to world known corporations.
  • High performance. WinpkFilter allows handling Gigabit network bandwidth in user mode application without noticeable performance degradation.
  • Complete and easy portability across all Windows desktop platforms.
  • Operates on RAS/PPP adapters and supports Windows 7 Mobile Broadband stack(PPIP)
  • Passive network listening (collecting network packets) and active filtering (with capability to edit/drop network packets) modes
  • Interface for injecting raw Ethernet frames into the network stack (either destined from the TCP/IP to the network and in reversed direction)
  • Support for MTU decrement (allows setting system-wide MTU decrement). This option is useful if you plan to add additional headers to IP packets (implement IP in IP packet tunneling, IPSEC based VPN and so on).
  • The powerful built-in network filters engine allows setting rules to pass, block or redirect a network packet to a Windows Packet Filter-based application for further processing.
Windows Packet Filter architecture
Windows Packet Filter architecture

Applicability/Usage Scope

Windows Packet Filter can be used as a base for the following kinds of network applications (including but not limited to):

  • User-mode firewall and content filtering solutions. No more need to write kernel mode drivers to implement the firewall!
  • Kernel-mode firewall and content filtering solutions. This requires kernel-mode programming skills and Source Code license (to integrate your network packet processing code directly into the drivers) but provides the maximum possible performance.
  • Internet Connection Sharing (Network Address Translation) that can be implemented either in user or kernel depending on performance requirements.
  • Virtual Private Network solution (IPSEC, SSL VPN, Wireguard etc.) that can also be implemented both in user and kernel depending on performance requirements.
  • Network packets tunneling solution. An example, packets captured from the network can be tunneled from the client to the remote system inside the SSL, SSH, HTTP, ICMP etc., extracted by the remote host and injected into the real network (after required packet headers modifications). Response packets can be returned to the client in the same manner. This may allow bypassing certain network access limitations.
  • Packet sniffer. You can capture and inspect all packets sent to (received from) TCP/IP.
  • IP shaping solutions (when you need to limit bandwidth for Internet users).
  • Network traffic counting and bandwidth management solutions.
  • Wireless Firewall Gateways, even with HTTP authorization.
  • Transparent proxy solution based on NDIS level packet redirection. This can be used, an example, to decrypt SSL(Man-In-The-Middle), parent content control, e-mail SPAM filtering etc…
  • Transparent filtering bridge


You can download Windows Packet Filter driver installer (free for personal(non-commercial), or educational (including non-profit organization) use) and samples binaries to test and evaluate the reliability and performance of our software.

The source code for Windows Packet Filter samples along with the latest NDISAPI library is available on GitHub.

Although NDISAPI library includes C++/CLI class library .NET developers can use an alternative p/Invoke C# library NDISAPI.NET

Driver packages:

Windows Packet Filter x64.msiWindows Vista* and laterDownload
Windows Packet Filter x86.msiWindows Vista* and laterDownload
Windows Packet Filter 95/98/ME/NT/2000/XP/2003Download


Basic and advanced native C++ samples binariesx64 buildsDownload
Basic and advanced native C++ samples binariesx86 buildsDownload
Basic native C++ samples binariesx86 VC++ 6.0 buildsDownload

Important notes:

  • Installed third-party firewall software may limit samples functionality.
  • Standard driver builds above limit the network MTU to 1500 bytes. It may cause performance degradation of 10 Gbps networks with Jumbo frames. Builds supporting Ethernet Jumbo frames (up to 9000 bytes) are available to licensed customers.

Windows Packet Filter Advanced Samples

  • Internet Gateway (snat.exe) is a simple MFC Internet Connection sharing application based on Windows Packet Filter. It implements a simple TCP and UDP dynamic NAT and allows sharing a single Internet connection over your home network providing the major Internet services (e-mail, WWW, FTP and etc…).
  • WAN Emulator (lfnemu.exe) is a simple console application for Windows based on Windows Packet Filter. It is also known as Long Fat Network (LFN) Emulator which primary task is simulating Long Fat Network behavior over normal Local Area Network by adding packets delays and drops.
  • capture – native C++ sample, intercepts packets for the specified network interface and saves those into the PCAP file, which can be opened and analyzed with WireShark.
  • dns_proxy – native C++ sample, redirects DNS protocol through the transparent UDP proxy.
  • dnstrace – native C++ sample, intercepts DNS responses and decodes their content to the console. Has configurations to link NDISAPI statically and dynamically.
  • ethernet_bridge – native C++ sample, implements bridging wired and wireless networks. More information
  • ipv6_parser – native C++ sample, intercepts IPv6 packets, matches to originated process (using IP Helper API) parses protocol headers.
  • sni_inspector – native C++ sample, intercepts network packets and extracts SNI from HTTPS packets and Host from HTTP packets.
  • socksify – native C++ sample, redirects selected TCP connections through a SOCKS5 proxy.
  • udp2tcp – native C++ sample, demonstrates how to convert UDP packets to TCP and vice versa to mask traffic.
  • TestDotNet – C# sample (using .NET C++/CLI NDISAPI library) demonstrates the NDISAPI usage in several filtering scenarios.


Windows Packet Filter is free for personal (non-commercial), or educational (including non-profit organization) use.

For the software publishers who wish to use Windows Packet Filter in their products, we offer two types of licenses. Each license includes one year of free updates & support and custom driver build*.

License typeComplete Source CodePrice (USD)Online Order
DeveloperNO3000.00Buy Now!
Source CodeYES9000.00Buy Now!
Developer to Source UpgradeYES6000.00Buy Now!

Please be careful when choosing the license type:

  • Developer license can be used for creating royalty-free Windows Packet Filter-based software. NT Kernel Resources strongly recommends you to request custom driver build* from us to use for production.
  • Source Code license is similar to Developer license, but it also includes complete source code of Windows Packet Filter.

* – You may need custom build of WinpkFilter drivers if you are going to redistribute helper drivers as a part of your software. Custom-builds allow avoiding any possible conflicts with other WinpkFilter based applications. If you have purchased a Developer license, you can request a custom build by sending e-mail to One custom build per license is included in Developer and Source Code subscriptions. Additional custom-builds are subject to extra charge of 100 USD per build.

Subscription Renewal

If you are already a Windows Packet Filter customer, but your support plan is out-of-date, then you can renew it using the links below (please note that NT Kernel Resources may request your previous order ID and date for confirmation):

License typeComplete Source CodePrice (USD)Online Order
Developer Subscription RenewNO2000.00Buy Now!
Source Code Subscription RenewYES6000.00Buy Now!


Please ask questions in our support forum.

* – due to EOL of SHA-1 code signing on December 1, 2020, it is no longer possible to sign drivers for Windows Vista/2008. To run Windows Packet Filter on these operating systems, you will need to use the Disable Driver Signing Enforcement option.