Line Loopback

Napatech Link-Capture™ Software Features

Intel® PAC
Napatech SmartNIC
Content Type
Feature Description
Capture Software Version
Link™ Capture Software 12.11

Line loopback enables frames received on a network port to be retransmitted to the same network port without involving the host CPU.


Frames are looped back to the same port without being modified. This includes the FCS which is not recalculated.

The line-loopback functionality and the filtering/capturing functionality can be used independently of each other. A port with line loopback enabled can at the same time be used to capture, for instance, all received IP frames.

Note: Line loopback and host loopback cannot be configured on a port at the same time.


The line-loopback functionality can be enabled using the config tool or using the NTAPI.

Using the config tool, apply the --line_loopback option as shown in the following command example.
# Enable line loopback on port 0.
/opt/napatech3/bin/config --cmd set --port 0 --line_loopback on
It can also be configured using the NT_ConfigWrite function with the NT_CONFIG_PARM_PORT_SETTINGS_V2 parameter and the NtPortSettings_v2_s structure. Set NtPortSettings_v2_s.lineLoopback to 0 or 1 (see DN-0449).