EXFO FTB-800 Series for FTB-1 - Manual (Page 67)

Test Setup - Test Applications
NetBlazer 57
Smart Loopback
Third-Party Remote Loopback
The Third-party Remote Loopback feature provides the capability to be
discovered and react to loop-up and loop-down commands from a third
party device. This feature is used for unidirectional testing, where the test
stream is transmitted from the third party device to a remote EXFO device.
The looped back test stream is received and analyzed by the third-party
device.
The third-party loopback supports three level of messages:

Layer 2: Only MAC addresses are swapped.

Layer 3: MAC and IP addresses are swapped.

Layer 4: MAC and IP addresses are swapped along with the UDP port.
To emulate a third-party remote device, the loopback mode is set in the
function of the layer of loop messages received. The loop messages are:

Layer 2: Ethernet

Layer 3: IP

Layer 4: UDP/TCP
On receipt of the third-party loop-up command as per requested layer, the
loopback mode is set and initiated on the module.