Host Loopback

Napatech Link-Capture™ Software Features

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

Host loopback enables frames transmitted from the host on a port to be received on the same port and to be delivered the host.


Host loopback enables frames transmitted on a port from the host or generated in the FPGA to be received on the same port and to be delivered to the host. The host-loopback feature is useful in a development environment to transmit and receive frames on the same host without a pluggable module or a physical link.

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


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

Using the config tool, apply the --host_loopback option as shown in the following command example.
# Enable host loopback on port 0.
/opt/napatech3/bin/config --cmd set --port 0 --host_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.hostLoopback to 0 or 1 (see DN-0449).
Note: The RX power of the pluggable module is turned off on a port with host loopback enabled. Any received frames from the remote host are therefore dropped.
Note: If host loopback is enabled on a port which is connected to a remote host, frames are transmitted to the remote host while the same frames are delivered to the local host. To stop transmitting frames to the remote host, turn the TX power off using the config tool. For example:
/opt/napatech3/bin/config --cmd set --port 0 --txpower off