[Vadim Smirnov]

I guess one reason could be because of how powerful the underlying CPU is.

It is easy to verify, just start Task Manager (or Resource Monitor) when you copy the file and check the CPU load with and without dnstrace running. If your CPU peaks even without dnstrace then no wonder if you get the throughput degradation when add extra work…

I want to measure how much overhead this project has if we use it to send every packet to user to check (block or not), and then send those that are OK based on user mode decision. So this dnstrace seems to do exactly this right?

Yes, it filters (takes from the kernel to user space and then re-injects back into the kernel) all packets passed through the specified network interface, selects DNS responses, decodes and dumps.

Can you also try to use the code that was shared on the blog that you mentioned to see if you still don’t get any reduced performance?

Well, dnstrace is good enough to test with. Also, if you would like to test with fast I/O option you can take sni_inspector. It also filters all the traffic for the selected interface, but instead DNS responses selects and dumps the SNI field from the TLS handshake.

[Vadim Smirnov]

The only idea I have is that you have some other third-party software (which includes NDIS/WFP filter) and somehow results the software conflict… Try to setup two fresh Windows connected over the switch or direct cable.

P.S. To ensure, retested with reversed copy direction and the result is still the same…

[Vadim Smirnov]

I’ve just taken dnstrace sample (dumps DNS packets and passes everything else without any special handling) and tried to copy one large file from the system running dnstrace to another one. Here is the result with dnstrace running and without:

.

[Vadim Smirnov]

The sample code you tested was designed for the demo purposes only. If you are interested in the performance tests you can check this post.

[Vadim Smirnov]

Capture tool was primarily designed for testing/debugging purposes and it utilizes relatively slow file stream I/O, e.g. each intercepted packet is delayed for the time needed to write it into the file resulting the increased latency and decreased bandwidth.

If you need a high speed traffic capture solution you have to implement in-memory packet caching and write captured packets into the file using dedicated thread instead of doing this in the packet filtering one. Or you could use use the memory mapped file and let Windows cache manager to do the rest 🤔

P.S. And yes, Fast I/O may improve the performance even further…

[Vadim Smirnov]

Windows 10 ARM64 is supported and driver build is available to registered customers.

[Vadim Smirnov]

You can change adapter mode calling SetAdapterMode without stopping the filtering or resetting events. Mode flag only defines what to do with an original packet, in listen mode it is passed over, in tunnel it is dropped.

[Vadim Smirnov]

This one seems to work just fine:

;-------------------------------------------------------------------------
; ndiswg_lwf.INF -- WinpkFilter NDIS LWF driver (WinTun build)
;
; Copyright (c) NT Kernel Resources.  All rights reserved.
;-------------------------------------------------------------------------
[version]
Signature   	= "$Windows NT$"
Class     	= NetService
ClassGUID  	= {4D36E974-E325-11CE-BFC1-08002BE10318}
Provider    = %Ntkr%
CatalogFile = ndiswg.cat
PnpLockdown	= 1

[Manufacturer]
%Ntkr%=Ntkr,NTx86,NTia64,NTamd64,NTARM64

[Ntkr.NTx86]
%ndiswg_Desc%=Install, nt_ndiswg

[Ntkr.NTia64]
%ndiswg_Desc%=Install, nt_ndiswg

[Ntkr.NTamd64]
%ndiswg_Desc%=Install, nt_ndiswg

[Ntkr.NTARM64]
%ndiswg_Desc%=Install, nt_ndiswg

;-------------------------------------------------------------------------
; Installation Section
;-------------------------------------------------------------------------
[Install]
AddReg=Inst_Ndi
Characteristics=0x40000
NetCfgInstanceId="{ACAA7086-8B4C-4443-B5CE-9694A907670C}"
Copyfiles = ndiswg.copyfiles.sys

[SourceDisksNames]
1=%ndiswg_Desc%,"",,

[SourceDisksFiles]
ndiswg.sys=1

[DestinationDirs]
DefaultDestDir=12
ndiswg.copyfiles.sys=12

[ndiswg.copyfiles.sys]
ndiswg.sys,,,2

;-------------------------------------------------------------------------
; Ndi installation support
;-------------------------------------------------------------------------
[Inst_Ndi]
HKR, Ndi,Service,,"ndiswg"
HKR, Ndi,CoServices,0x00010000,"ndiswg"
HKR, Ndi,HelpText,,%ndiswg_HelpText%
HKR, Ndi,FilterClass,, compression
HKR, Ndi,FilterType,0x00010001,0x00000002
HKR, Ndi\Interfaces,UpperRange,,"noupper"
HKR, Ndi\Interfaces,LowerRange,,"ndis5,ndis4"
HKR, Ndi\Interfaces, FilterMediaTypes,,"ethernet, wan, ppip, bluetooth, ndis5, nolower"
HKR, Ndi,FilterRunType, 0x00010001, 1 ;this filter must run before any protocol can bind to the below miniport 

;-------------------------------------------------------------------------
; Service installation support
;-------------------------------------------------------------------------
[Install.Services]
AddService=ndiswg,,ndiswg_Service_Inst

[ndiswg_Service_Inst]
DisplayName     = %ndiswg_Desc%
ServiceType     = 1 ;SERVICE_KERNEL_DRIVER
StartType       = 1 ;SERVICE_SYSTEM_START
ErrorControl    = 1 ;SERVICE_ERROR_NORMAL
ServiceBinary   = %12%\ndiswg.sys
LoadOrderGroup  = NDIS
Description     = %ndiswg_Desc%
AddReg          = NdisImPlatformBindingOptions.reg

[Install.Remove.Services]
DelService=ndiswg,0x200

[NdisImPlatformBindingOptions.reg]
HKR, Parameters, NdisImPlatformBindingOptions,0x00010001,2

[Strings]
Ntkr = "NT Kernel Resources"
ndiswg_Desc = "WinpkFilter LightWeight Filter for WinTun"
ndiswg_HelpText = "WinpkFilter NDIS LightWeight Filter for WinTun"

[Vadim Smirnov]

Try to add ‘ndis5’ to the list and let me know if it helped.

[Vadim Smirnov]

Windows Packet Filter NDIS filter driver does not bind to WinTun network adapter because of the following in wintun.inf:

HKR, Ndi\Interfaces, LowerRange, , "nolower"

while in ndisrd_lwf.inf we have:

HKR, Ndi\Interfaces, FilterMediaTypes,,"ethernet, wan, ppip, bluetooth"

So there are two choices:

• Change wintun.inf ‘nolower’ to ‘ethernet’
• Add ‘nolower’ to the list of FilterMedia types in ndisrd_lwf.inf

As a side effect second option will cause Windows Packet Filter driver binding to the interfaces it normally would not bind to and therefore it is not supported by stock driver build.

[Vadim Smirnov]

Then there must be something wrong with your modified SYN packet. Enable checksum verification in Wireshark and check if packet checksums are good.

[Vadim Smirnov]

From what I can see there is no SYN-ACK packet from your HTTP server. So,

• Does your HTTP server listen on port 153?
• Check if HTTP server if firewall protected and disable Windows Defender firewall if the server is Windows.

[Vadim Smirnov]

First I would check if packet are delivered to the destination. You could setup the HTTP server in the LAN and try to connect to it while capturing traffic using tcpdump/wireshark (on the server). For the TCP connection you must see the incoming TSP SYN and if the SYN is OK then also the outgoing SYN_ACK.

[Vadim Smirnov]

The approach looks good in general. I hope you remember to recalculate IP/TCP checksum and adjust MAC addresses accordingly.

[Vadim Smirnov]

Yes, it is possible to do using Windows Packet Filter, however:

1. this is not trivial, as you need to write the code to select and re-route network packets
2. implementation may depend on VPN you are using, so I would recommend to start with something simple, e.g. routing ICMP PING or DNS

[Author]

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