Configuring WinPcap-NT

Napatech Link-Capture™ Software and WinPcap-NT Installation Guide for Windows

Napatech SmartNIC
Content Type
Software Installation Guide
Capture Software Version
Link™ Capture Software 12.8


The WinPcap-NT library works on devices explicitly created and assigned to a stream in the ntpcap.ini configuration file as well as streams created, for instance, by using the ntpl tool. For each stream a virtual device is created.

Existing streams

Each stream not created by ntpcap.ini appears to WinPcap as a device named nt3g<n>, where <n> is the stream ID. Examples of names are: nt3g0 and nt3g1. Only streams created by ntpcap.ini have TX capabilities in WinPcap.

Streams defined in the ntpcap.ini file

The configuration file ntpcap.ini is read whenever a WinPcap application initializes its device list.

WinPcap devices corresponding to streams defined in the ntpcap.ini file have user-defined names. The names are defined in the ntpcap.ini file, which must have the format described in Format of the ntpcap.ini File. Streams defined in the ntpcap.ini file can have both RX and TX capabilities in WinPcap.

Default ntpcap.ini and setup.ini

A default ntpcap.ini file is installed in the %NAPATECH3_ROOT%\config directory (see The Default ntpcap.ini File).

You can edit ntpcap.ini manually. However, you can also specify more suitable parameter values in another configuration file, setup.ini. If ntservice.ini does not exist and setup.ini exists when NTService starts, the parameters specified in setup.ini will be used to populate a new ntservice.ini (the configuration file for NTService) and create or overwrite ntpcap.ini.

For more information about parameters supported by setup.ini, please refer to the file %NAPATECH3_ROOT%\config\example_setup.ini, which will be installed if you install WinPcap-NT.

Considerations on allocation of TX host buffers

When TX capabilities are defined for a WinPcap device in the ntpcap.ini file, one TX host buffer is used for each application that opens the device. This is in contrast to RX, where all applications share the same host buffers created by NTPL and associated with a stream ID. The maximum number of RX and TX host buffers are specified in the ntservice.ini file (see DN-0449).

Note: In the default ntservice.ini file 4 TX host buffers are allocated, and in the default ntpcap.ini file, 4 WinPcap devices (napa0, napa1, napa2, and napa3) with TX capabilities are defined (see The Default ntpcap.ini File). So when all 4 devices are opened, all 4 available TX host buffers are used, and an attempt from a new application to open one of the 4 devices and thereby use a fifth host buffer will fail. The solution is to allocate more TX host buffers in the ntservice.ini file, or to remove TX capabilities in the ntpcap.ini file for devices not needing them.