EXFO FTB-800 Series for FTB-1 - Manual (Page 228)

Test Setup - Test Configurator, Timer, and System
218 FTB-700G/800 Series
Smart Loopback
Smart Loopback
Note: The Smart Loopback block is only displayed when the Transparent
(Pseudo-Physical) check box is cleared (see Loopback Mode on page 93).
From the Test menu, tap Setup, Test Configurator, and the Smart
Loopback block.
Loopback

Mode determines at which layer the Smart Loopback address/port
swapping operation will be.

Ethernet swaps the MAC addresses of received packets having
their Destination MAC address matching the MAC address of the
loopback port.

Ethernet (All Unicast) swaps the MAC addresses of received
packets having Unicast Destination MAC address.

IP, for Ethernet Layer 3 and 4, swaps the MAC and IP addresses of
received packets having their Destination IP address matching the
IP address of the loopback port. For Ethernet Layer 2, swaps the
MAC addresses for packets having their Destination MAC address
matching the MAC address of the loopback port.

UDP/TCP (default), for Ethernet Layer 4, swaps the UDP or TCP
ports and the MAC and IP addresses of received packets having
their Destination IP address matching the IP address of the
loopback port. For Ethernet Layer 3, swaps the MAC and IP
addresses for packets having their Destination IP address
matching the IP address of the loopback port. For Ethernet Layer 2,
swaps the MAC addresses for packets having their Destination
MAC address matching the MAC address of the loopback port.

Matching & Swapping indicates the Loopback parameters that will be
used based on the Loopback Mode selected.