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<sect1 id="npcap-users-guide">
<title>Npcap Users' Guide</title>
<sect1info>
<abstract>
<para>The Users' Guide covers the basics of installing and removing
Npcap, interactions with WinPcap, frequently asked questions,
and how to report bugs.</para>
</abstract>
</sect1info>
<para>Because Npcap is a packet capture architecture, not merely a software
library, some aspects of installation and configuration may fall to the end
user. This Users' Guide covers the basics of installing, configuring, and
removing Npcap, as well as how to report bugs.</para>
<sect2 id="npcap-installation">
<title>Installation</title>
<para>
Npcap is distributed as a signed executable installer, downloadable from
<ulink url="https://nmap.org/npcap/#download">Nmap.com</ulink>. Major
versions are backwards-compatible, and users of the free non-commercial
version are encouraged to upgrade regularly for security and stability
fixes. Software distributors may have separate requirements for supported
Npcap versions. Please refer to
<ulink url="http://www.npcap.org/#License">the Npcap License</ulink> for
terms of use and redistribution.</para>
<para>
The Npcap installer and uninstaller are easy to use in
<quote>Graphical Mode</quote> (direct run) and <quote>Silent Mode</quote> (run with
<option>/S</option> parameter, available only with <ulink url="https://nmap.org/npcap/oem/">Npcap OEM</ulink>).
</para>
<sect3 id="npcap-installation-options">
<title>Installer options</title>
<para>
The installer accepts several command-line options that correspond to the
options presented in the graphical interface (GUI). The options can be
set by command-line flags taking the form
<option>/<replaceable>name</replaceable>=<replaceable>value</replaceable></option>.
</para>
<para>The values for these options must be one of:
</para>
<itemizedlist>
<listitem><para><option>yes</option>: select the option</para></listitem>
<listitem><para><option>no</option>: unselect the option</para></listitem>
<listitem><para><option>enforced</option>: select the option and make it unchangable in the GUI</para></listitem>
<listitem><para><option>disabled</option>: unselect the option and make it unchangable in the GUI</para></listitem>
</itemizedlist>
<sect4 id="npcap-installer-options-gui">
<title>Graphical installer options</title>
<para>The following options are presented as checkboxes in the
installer, but can be set or locked via command-line flags. Unless
otherwise noted, the default for these options is <option>no</option>.
</para>
<variablelist>
<varlistentry>
<term><option>/loopback_support</option></term>
<listitem><para>
<emphasis>Legacy loopback support for Nmap 7.80 and older. Not needed for Wireshark.</emphasis>
Older versions of Npcap required a Microsoft KM-TEST loopback
adapter to be installed in order to capture and inject loopback
traffic. This is no longer needed, but some software won't be
able to do loopback injection unless the adapter is installed.
Use this option to install the legacy loopback adapter if
needed.
</para>
<para>See <xref linkend="npcap-feature-loopback" /> for more
information.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/admin_only</option></term>
<listitem><para>
<emphasis>Restrict Npcap driver's access to Administrators
only</emphasis>. When this option is chosen, the devices
created by the Npcap driver for capture and injection on each
network adapter will be created with a restrictive ACL that
only allows access to the device by the SYSTEM and built-in
Administrators. Because this level of access requires UAC
elevation, a helper binary, <literal>NpcapHelper.exe</literal>,
is used to request elevation for each process that opens a
capture handle.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/dot11_support</option></term>
<listitem><para>
<emphasis>Support raw 802.11 traffic (and monitor mode) for
wireless adapters</emphasis>. This option installs a second
Lightweight Filter Driver that uses the Native WiFi API to
capture raw 802.11 WiFi frames on devices that are put into
network monitor mode. Captured frames are given a Radiotap
header. Not all hardware or network drivers support the Native
WiFi API.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/winpcap_mode</option></term>
<listitem><para>
<emphasis>Install Npcap in WinPcap API-compatible
Mode</emphasis>. The default for this option is
<option>yes</option> in Npcap 0.9985 and later. Npcap's DLLs
have always been installed into a separate
<literal>Npcap</literal> subdirectory of the system
directory to avoid conflicting with existing WinPcap
installations. This option also installs the DLLs to the
system directory, replacing WinPcap. Any existing WinPcap
installation will be removed.
</para>
<para>
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/prior_driver</option></term>
<listitem><para>
<emphasis>Install older driver</emphasis>. Microsoft continues to tighten their policy on what
types of certificates and authorities may sign drivers. In cases where the current driver may
not strictly meet these requirements, the <option>/prior_driver</option> option may be used to
install the last version of the driver that meets these requirements. In cases where no such
driver exists, this option is ignored.
</para>
<para>
</para></listitem>
</varlistentry>
</variablelist>
</sect4>
<sect4 id="npcap-installer-options-cli">
<title>Command-line installation options</title>
<para>Some advanced or deprecated options are only available on the
command-line. Options marked <literal>(deprecated)</literal> are
subject to removal in future versions.</para>
<variablelist>
<varlistentry>
<term><option>/S</option> (Silent install, Npcap OEM only)</term>
<listitem><para>
Installs Npcap without showing any graphical windows or
prompts. Silent install is available only for Npcap OEM.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/disable_restore_point</option></term>
<listitem><para>
The default for this option is <option>yes</option>, so the
installer will not set a system restore point. Windows may
independently create a restore point because of the driver
installation independent from this option. To ensure a
restore point is made, specify
<option>/disable_restore_point=no</option>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/no_kill</option></term>
<listitem><para>
Control termination of
processes using Npcap during upgrades or WinPcap when
<option>/winpcap_mode=yes</option> is chosen. See
<xref linkend="npcap-installation-uninstall-options" />
for more detailed discussion.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/D</option> (destination directory)</term>
<listitem><para>
The destination directory for installation can be overridden by
the <option>/D</option> option, with a few restrictions. First, it will
only affect where Npcap keeps its installation logs and helper utilities.
The driver and DLLs will always be installed into the appropriate
directories below <command>%SYSTEMROOT%\System32\</command>. Second, the
<option>/D</option> must be the last option in the command, and the path
must not contain quotes. For example, to change the installation directory
to <filename>C:\Path With Spaces\</filename>, the invocation would be:
<command>npcap-<replaceable>version</replaceable>.exe /D=C:\Path With Spaces</command>
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/npf_startup</option> (deprecated)</term>
<listitem><para>
<emphasis>Automatically start the Npcap driver at boot
time</emphasis>. This option defaults to
<option>yes</option>, because Windows expects NDIS filter
drivers to be available at boot time. If you choose to disable
this, Windows may not start networking for up to 90 seconds
after boot.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>/vlan_support</option> (deprecated, ignored)</term>
<listitem><para>
<emphasis>Support 802.1Q VLAN tag when capturing and sending
data (currently unsupported)</emphasis>. This feature was
disabled in 2016 to prevent a crash and has not been
re-enabled.
</para></listitem>
</varlistentry>
</variablelist>
</sect4>
</sect3>
<sect3 id="npcap-installation-uninstall-options">
<title>Uninstaller options</title>
<para>
The uninstaller provided with Npcap also accepts some command-line options.
</para>
<variablelist>
<varlistentry>
<term><option>/S</option> (Silent uninstall)</term>
<listitem>
<para>Uninstalls Npcap without showing any graphical windows or
prompts. Silent uninstall is available in all editions of Npcap,
not just Npcap OEM. If Npcap OEM installer in silent mode needs
to uninstall an older Npcap installation, it passes the
<option>/S</option> option to the existing uninstaller.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>/Q</option> (Quick uninstall)</term>
<listitem>
<para>Skips the confirmation page and finish page in the uninstall
wizard. This option does not have any meaning for silent
uninstalls.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>/no_kill</option>=<replaceable>yes|no</replaceable> (do not kill processes)</term>
<listitem>
<para>Controls how the uninstaller handles processes that are still using
Npcap at the time of uninstall. The default value is
<literal>no</literal>, which allows the uninstaller to terminate
processes that would block Npcap from being uninstalled. If
<option>/no_kill=yes</option> is specified, then Npcap
uninstaller will fail if there are still applications using Npcap
driver or DLLs.</para>
<para>In the default case, <option>/no_kill=no</option>, the
graphical uninstaller will give the user the choice to manually
close the offending programs, have the uninstaller terminate
them, or abort the uninstallation. In silent mode, Npcap
uninstaller will immediately terminate any command-line processes
that are using Npcap (like a Nmap process that is still
scanning), and wait for at most 15 seconds to gracefully
terminate any GUI processes that are using Npcap (like Wireshark
UI that is still capturing). <quote>Gracefully</quote> means
that if you are still capturing via Wireshark, Wireshark UI will
prompt the user about whether to save the current capture before
closing. The user will have 15 seconds to save his session.
<emphasis>Note:</emphasis> although Npcap uninstaller won't
terminate Wireshark UI processes immediately, the live capture
stops immediately. This is because Wireshark UI uses command-line
processes named <varname>dumpcap.exe</varname> to capture, and
that command-line process will be terminated immediately.</para>
<para>If this option is provided on the
<emphasis>installer</emphasis> command line, it will be passed to
the Npcap uninstaller when doing an upgrade or
replacement.</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="npcap-installation-options-disabled">
<title>Disabled and enforced options for GUI Mode</title>
<para>
We may disable or enforce certain options in the installer GUI to make them unselectable. This
usually means that those options can easily cause compatibility issues and are considered
not suitable for most users, or we think we need to enforce some rules for the Npcap API. Advanced users can still change their states via command-line
parameters, which is described in following sections.
</para>
<para>
Fortunately, if a distributor wants to start the Npcap installer GUI and disable or enforce
certain options for reasons like compatibility. It can also use the four value
mechanism by setting the command-line parameters to <option>disabled</option> or <option>enforced</option>.
For example, the following command will start an installer GUI with the
<option>loopback_support</option> option disabled and unselected:
</para>
<para>
<command>npcap-<replaceable>version</replaceable>.exe /loopback_support=disabled</command>
</para>
</sect3>
</sect2>
<sect2 id="npcap-platforms">
<title>Windows platforms supported</title>
<para>Npcap supports all Windows versions currently supported by Microsoft. Depending on Windows version, the
driver may support a different NDIS version, which corresponds to a set of network stack
features.</para>
<itemizedlist>
<listitem>
<para>On <emphasis>Windows 10</emphasis>, <emphasis>Windows Server 2016</emphasis>, and
<emphasis>Windows Server 2019</emphasis>, Npcap installs a NDIS 6.50
driver.</para></listitem>
<listitem>
<para>On <emphasis>Windows 8.1</emphasis>, <emphasis>Windows 8</emphasis>,
<emphasis>Windows Server 2012 R2</emphasis>, and
<emphasis>Windows Server 2012</emphasis>,
Npcap installs a NDIS 6.30 driver.</para></listitem>
<listitem>
<para>On <emphasis>Windows 7</emphasis> and <emphasis>Windows Server 2008 R2</emphasis>, Npcap
installs a NDIS 6.20 driver.</para></listitem>
</itemizedlist>
<para>Microsoft will end Extended support for Windows versions prior to Windows 10 on January 10, 2023. After
that time, new Npcap releases <emphasis>may</emphasis> omit support for these operating
systems.</para>
<para>Npcap can be installed on x86, x86-64, and ARM64. DLLs for the native architecture will be installed, as
well as x86 DLLs for applications running in 32-bit emulation.</para>
</sect2>
<sect2 id="npcap-feature-dot11-wireshark">
<title>How to use Wireshark to capture raw 802.11 traffic in <quote>Monitor Mode</quote></title>
<para>
The latest Wireshark has already integrated the support for Npcap's <quote>Monitor Mode</quote> capture.
If you want to use Wireshark to capture raw 802.11 traffic in <quote>Monitor Mode</quote>, you need to
switch on the monitor mode inside the Wireshark UI instead of using <xref linkend="npcap-feature-dot11-wlanhelper" />.
This is because Wireshark only recognizes the monitor mode set by itself. So when you turn
on monitor mode outside Wireshark (like in <filename>WlanHelper</filename>), Wireshark will not know the adapter
has been in monitor mode, and will still try to capture in Ethernet mode, which will get no traffic.
<!-- TODO: Change instructions in other sections to reflect this. Verify that it is correct, first -->
So after all, the correct steps are:
</para>
<itemizedlist>
<listitem><para>Install latest version Wireshark and latest version Npcap with
<option>Support raw 802.11 traffic</option> option checked.</para></listitem>
<listitem><para>Launch Wireshark QT UI (GTK version is similar), go to <quote>Capture options</quote>.
Then toggle the checkbox in the <quote>Monitor Mode</quote> column of your wireless adapter's row.
Click the <quote>Start</quote> button. If you see a horizontal line instead of the checkbox,
then it probably means that your adapter doesn't support monitor mode. You can use the
<filename>WlanHelper</filename> tool to double-check this fact.</para></listitem>
<listitem><para>To decrypt <emphasis>encrypted 802.11 data</emphasis>
packets, you need to specify the decipher key in Wireshark, otherwise
you will only see 802.11 data packets.</para></listitem>
<listitem><para>Stop the capture in Wireshark UI when you finishes capturing, the monitor mode
will be turned off automatically by Npcap.</para></listitem>
</itemizedlist>
</sect2>
<sect2 id="npcap-qa">
<title>Q & A</title>
<itemizedlist>
<listitem><para>Network interruption while installing Npcap: Installing a filter driver may
cause brief interruptions to network connectivity based on the specific changes needed
to install the driver in the network stack. This known issue is documented as
<ulink role="hidepdf" url="">issue #53</ulink> on our tracker.</para>
<para> A separate issue is a longer interruption in connectivity if the
<varname>npcap</varname> service is not started, which used to be an installer option.
As Microsoft states <ulink role="hidepdf" url="https://support.microsoft.com/en-us/kb/2019184">here</ulink>,
<emphasis>an optional NDIS light-weight filter (LWF) driver like Npcap could cause
90-second delay in network availability</emphasis>. Some solutions you could try
are: 1) wait for 90 seconds; 2) disable and re-enable the adapter icon in
<command>ncpa.cpl</command>; 3) reboot. If the network is still unable to connect,
please <ulink role="hidepdf" url="http://issues.npcap.org/new?title=Npcap+Bug+Report">file a bug report</ulink>.
</para></listitem>
<listitem><para>Installation fails with error code <varname>0x8004a029</varname>:
The cause is that you have <quote>reached the maximum number of network filter
drivers</quote>, see solution
<ulink role="hidepdf" url="https://social.technet.microsoft.com/Forums/windows/en-US/4deb27fc-33ce-4fc0-a26f-3fec5b57733d/is-there-a-maximum-number-of-network-filter-drivers-in-windows-7?forum=w7itpronetworking">here</ulink>.
</para></listitem>
<listitem><para>Npcap Loopback Adapter is missing (legacy loopback support):
The legacy Npcap Loopback Adapter is actually a wrapper of Microsoft Loopback Adapter.
Such adapters won't show up in Wireshark if the <varname>Basic Filtering Enging (BFE)</varname>
service was not running. To fix this issue, you should start this service at <varname>services.msc</varname>
manually and restart the Npcap service by running <command>net stop npcap</command>
and <command>net start npcap</command>. See details about this issue
<ulink role="hidepdf" url="https://github.com/nmap/nmap/issues/802">here</ulink>.
</para></listitem>
<listitem><para>Npcap only captures TCP handshake and teardown, but not data packets.
Some network adapters support offloading of tasks to free up CPU time for
performance reasons. When this happens, Npcap may not receive all of the
packets, or may receive them in a different form than is actually sent on the
wire. To avoid this issue, you may disable TCP Chimney, IP Checksum
Offloading, and Large Send Offloading in the network adapter properites on
Windows. See details about this issue in
<ulink role="hidepdf" url="https://github.com/nmap/nmap/issues/989">issue
#989</ulink> on our tracker.
</para></listitem>
</itemizedlist>
</sect2>
<sect2 id="npcap-issues">
<title>Reporting Bugs</title>
<para>
Please report any bugs or issues about Npcap on
<ulink role="hidepdf" url="http://issues.npcap.org/new?title=Npcap+Bug+Report">the Nmap Project's Issues tracker</ulink>.
In your report, please provide your <emphasis>DiagReport</emphasis> 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.
</para>
<sect3 id="npcap-issues-diagreport">
<title>Diagnostic report</title>
<para>
Npcap has provided a diagnostic utility called <filename>DiagReport</filename>.
It provides a lot of information including OS metadata, Npcap related files,
install options, registry values, services, etc. You can simply click the
<filename>C:\Program Files\Npcap\DiagReport.bat</filename> file to run <filename>DiagReport</filename>.
It will pop up a text report via Notepad (it's stored in: <filename>C:\Program Files\Npcap\DiagReport.txt</filename>).
Please always submit it to us if you encounter any issues.
</para>
</sect3>
<sect3 id="npcap-issues-installation-log">
<title>General installation log</title>
<para>
Npcap keeps track of the installation in a log file:
<filename>C:\Program Files\Npcap\install.log</filename>. Please submit it
together in your report if you encounter issues during the installation
(e.g. the installer halts).
</para>
</sect3>
<sect3 id="npcap-issues-driver-installation-log">
<title>Driver installation log</title>
<para>
Npcap keeps track of the driver installation (aka commands run by
<filename>NPFInstall.exe</filename>) in a log file:
<filename>C:\Program Files\Npcap\NPFInstall.log</filename>, please submit
it together in your report if you encounter issues during the driver
installation or problems with the <quote>Npcap Loopback Adapter</quote>.
</para>
<para>
There's another system-provided driver installation log in:
<filename>C:\Windows\INF\setupapi.dev.log</filename>.
If you encounter errors during the driver/service installation, please copy
the Npcap-related lines out and send them together in
your report.
</para>
</sect3>
<sect3 id="npcap-issues-packet-log">
<title>Dynamic link library (DLL) log</title>
<para>
For problems with Npcap's regular operation, you may need to obtain a
debug log from <filename>Packet.dll</filename>. To do this, you will
need a debug build of Npcap. If you are a Npcap developer, you can build
the <filename>Packet.sln</filename> project with the
<varname>_DEBUG_TO_FILE</varname> 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
(<filename>C:\Program Files\Npcap\Packet.log</filename>), so you may want
to delete it after an amount of time, or save your output to another
place before it gets too large.
</para>
</sect3>
<sect3 id="npcap-issues-driver-log">
<title>Driver log</title>
<para>
If there is an issue with the Npcap driver, you can open an
<emphasis>Administrator</emphasis> command prompt, enter <command>sc query
npcap</command> to query the driver status and <command>net start
npcap</command> to start the driver (replace
<replaceable>npcap</replaceable> with <replaceable>npf</replaceable> if you
installed Npcap in <quote>WinPcap Compatible Mode</quote>). 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 <ulink role="hidepdf"
url="https://technet.microsoft.com/en-us/sysinternals/debugview.aspx">DbgView</ulink>
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.
</para>
</sect3>
<sect3 id="npcap-issues-bsod">
<title>Blue screen of death (BSoD) dump</title>
<para>
If you encountered BSoD when using Npcap, please attach the minidump
file (in <filename>C:\Windows\Minidump\</filename>) to your report
together with the Npcap version. We may ask you to provide the full
dump (<filename>C:\Windows\MEMORY.DMP</filename>) for further troubleshooting.
</para>
</sect3>
</sect2>
</sect1>