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Npcap Users' Guide

Reporting Bugs

Please report any bugs or issues about Npcap on the Nmap Project's Issues tracker. In your report, please provide your DiagReport output, user software version (e.g. Nmap, Wireshark), steps to reproduce the problem, and other information you think necessary. If your issue occurs only on a particular OS version (e.g. Win10 1511, 1607), please mention it in the report.

Diagnostic report

Npcap has provided a diagnostic utility called DiagReport. It provides a lot of information including OS metadata, Npcap related files, install options, registry values, services, etc. You can simply click the C:\Program Files\Npcap\DiagReport.bat file to run DiagReport. It will pop up a text report via Notepad (it's stored in: C:\Program Files\Npcap\DiagReport.txt). Please always submit it to us if you encounter any issues.

For Vista users: DiagReport is a script written for Windows PowerShell, and Vista doesn't have it installed by default. So if you are using Vista, you need to install PowerShell 2.0 (KB968930) on your system. Please download it here for x86 and here for x64. Win7 and later systems have built-in PowerShell support and don't need to do anything about it.

General installation log

Npcap keeps track of the installation in a log file: C:\Program Files\Npcap\install.log. Please submit it together in your report if you encounter issues during the installation (e.g. the installer halts).

Driver installation log

Npcap keeps track of the driver installation (aka commands run by NPFInstall.exe) in a log file: C:\Program Files\Npcap\NPFInstall.log, please submit it together in your report if you encounter issues during the driver installation or problems with the Npcap Loopback Adapter.

There's another system-provided driver installation log in: C:\Windows\INF\setupapi.dev.log. If you encounter errors during the driver/service installation, please copy the Npcap-related lines out and send them together in your report.

Dynamic link library (DLL) log

For problems with Npcap's regular operation, you may need to obtain a debug log from Packet.dll. To do this, you will need a debug build of Npcap. If you are a Npcap developer, you can build the Packet.sln project with the _DEBUG_TO_FILE macro defined. If you are an end user, you can contact the Npcap development team for the latest Npcap debug build. The debugging process will continue to append to the debug log (C:\Program Files\Npcap\Packet.log), so you may want to delete it after an amount of time, or save your output to another place before it gets too large.

Driver log

If there is an issue with the Npcap driver, you can open an Administrator command prompt, enter sc query npcap to query the driver status and net start npcap to start the driver (replace <npcap> with <npf> if you installed Npcap in WinPcap Compatible Mode). The command output will inform you whether there's an error. If the driver is running well, but the issue still exists, then you may need to check the driver's log. Normal Npcap releases don't switch on the driver log function for performance. Contact the Npcap development team to obtain a driver-debug version of the Npcap installer. When you have got an appropriate driver-debug version Npcap, you need to use DbgView to read the Windows kernel log (which contains our driver log). You may need to turn on DbgView before installing Npcap, if the error occurs when the driver loads. When done, save the DbgView output to a file and submit it in your report.

Blue screen of death (BSoD) dump

If you encountered BSoD when using Npcap, please attach the minidump file (in C:\Windows\Minidump\) to your report together with the Npcap version. We may ask you to provide the full dump (C:\Windows\MEMORY.DMP) for further troubleshooting.

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