Exactly as described, this sets the minimum depth of header-field swapping -- Layer 2 only, or Layer 2 through Layer 3 IPv4 or IPv6 -- this reflector entity performs when looping test traffic back, matching whatever network the test traffic actually traverses. Choosing too shallow a level, such as l2only, when the test path actually crosses an IP network means the reflector won't swap source and destination IP and port fields correctly, causing the returning test traffic to be misrouted or misclassified rather than reflected cleanly back to the generator. For example, a benchmark test crossing a routed IPv6 core needs this set to l2ToL3IPv6only so the reflector swaps IPv6 addresses in addition to MAC addresses; leaving it at l2only would break the loop test over that path.