TP-Link MC100CM User Manual page 14

With the Link Fault Pass Through function enabled (optional with
switch LFP), TP port and FX port of the same converter will inform
each other the fault link status so that when one side of the link fails,
the other side will force the link to shut down as soon as noticed. The
procedure will be illustrated as shown below.
If link fail happens on TP port (A), the FX port (A) sends non-idle
pattern to notice the FX port (B). The FX port (B) then forces its TP
port (B) to link failed after receiving the non-idle pattern. Link status
LED will also be off for both Converters and Devices as shown below.
Device A
Device B
Converter A
Converter B
Off
Off
FX_LFP FX_Link/Act
On
On
8
Link LED
TP_Link/Act
Off
Off
Off
Off