EXFO ETS-1000G - Manual (Page 67)

10 Gigabit Ethernet Analyzer 57
9 Loopback
The loopback feature is used for testing networks in compliance with RFC
2544, measuring BER and solving some other tasks. It allows looping back
the traffic coming to the device on the four OSI layers.
On the physical layer (L1) all incoming traffic is left unchanged and
redirected back. Besides, statistics of received traffic is collected.
On the data link layer (L2) all incoming frames are redirected back, the
source and destination MAC addresses may be swapped. Statistics of
received and transmitted traffic is collected.
On the network layer (L3) all incoming packets are redirected back, the
source and destination MAC and IP addresses are swapped. Statistics of
received and transmitted traffic is collected.
On the transport layer (L4) all incoming traffic is redirected back. In
addition to swapping the source and destination MAC and IP addresses,
the source and destination TCP/UDP port numbers are swapped too.
Note: Defective packets are not redirected in case of setting up a loopback on the
data link (L2), network (L3) and transport (L4) layers.
Note: Packets with identical MAC Dst and MAC Src, M Protocol Data Units
(OAMPDU) and ARP requests which are contained in the incoming traffic
are not redirected in case of setting up a loopback on the data link (L2),
network (L3) and transport (L4) layers.
Note: If an incoming packet contains an MPLS label, it will be redirected without
changing the label value.