EXFO ETS-1000 - Manual (Page 48)

Connecting Unit
40 ETS-1000
Unit Connection Schemes
Unit Connection Scheme 3
Unit Connection Scheme 4
The scheme 1 shows the connection of the analyzer (using one
analyzer’s port) to the network with equipment operating on the Data
Link layer (for example, network switch). In this case, generated test
traffic should be rerouted back to the analyzer via the loopback. At the
DUT, source and destination MAC addresses are swapped in the
incoming packets, and the test stream is retransmitted back to the
source port on the analyzer.