The Napatech libpcap 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.
Each stream not created by ntpcap.ini appears to libpcap 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 libpcap.
Streams defined in the ntpcap.ini file
The configuration file ntpcap.ini is read whenever a libpcap application initializes its device list.
libpcap 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 libpcap.
You can create a new ntpcap.ini file from scratch in /opt/napatech3/config/ or copy a default ntpcap.ini file to /opt/napatech3/config/.
If you have installed libpcap using package_install_3gd-x.y.z.sh, a default ntpcap.ini file has been copied to /opt/napatech3/config (see The Default ntpcap.ini File).
If you have installed libpcap using the procedure in Installing libpcap with Napatech Extensions, you can use the procedure in Copy the ntpcap.ini File to Use Defined Streams to copy a default ntpcap.ini file to /opt/napatech3/config.
Considerations on allocation of TX host buffers
When TX capabilities are defined for a libpcap 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).