EXFO ETS-1000L - Manual (Page 17)

Ethernet Tester Analyzer 11
4 Loopback
The Loopback function is necessary for networks testing in compliance
with the RFC 2544, as well as for a number of other tasks. This function
allows to test the network without changing it’s settings.
Network testing with the Loopback function can be performed at the four
OSI layers, jumbo frames are supported (up to 9600 bytes).

At the Physical layer (L1) all the incoming traffic is being retransmitted
backward without changing.
All the connection schemes use the following notation:

MAC Src: indicates the source MAC address

MAC Dst: indicates the destination MAC address

IP Src: indicates the source IP address

IP Dst: indicates the destination IP address

TCP/UDP Dst: indicates the destination TCP/UDP port number

TCP/UDP Src: indicates the source TCP/UDP port number