Line Loopback

Napatech Link-Capture™ Software Features
Platform
Napatech SmartNIC
Content Type
Feature Description
Capture Software Version
Link™ Capture Software 12.16

Line loopback returns incoming traffic from the network back out on the same physical port without involving the host CPU. It loops frames arriving from the remote link directly back to the link.

Features

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.
Figure. Line-loopback traffic path
Page-1 Rounded Rectangle.19 Remote server Remote server Dynamic connector Dynamic connector.47 Rounded Rectangle.32 Server Server Sheet.5 L Shape Sheet.7 Round Corner Rectangle SmartNIC SmartNIC Round Corner Rectangle.24 Round Corner Rectangle.25 Round Corner Rectangle.26 Round Corner Rectangle.27 Round Corner Rectangle.28 Round Corner Rectangle.29 Round Corner Rectangle.30 Round Corner Rectangle.31 Round Corner Rectangle.33 Round Corner Rectangle.34 L Shape.38 Sheet.20 Port 0 Port 0 Sheet.21 Port 1 Port 1 Sheet.23 Incoming traffic Incoming traffic Sheet.24 Outgoing traffc Outgoing traffc Rounded Rectangle.25 Host Host Sheet.26 Line lookback active Line lookback active

Configuration

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).