Methods and systems for Ethernet fabric protection in a disaggregated OTN switching system that include PIU modules each having multiple ports for OTN to Ethernet transceiving and an Ethernet fabric as a switching core are disclosed. An OTN over Ethernet module in each of the PIU modules may enable various OTN functionality to be realized using the Ethernet fabric which may include multiple Ethernet switches. A first PIU module may detect a fault condition on an Ethernet fabric plane of the Ethernet fabric. In response to the detection, the OTN switching system may transmit the fault condition to other PIU modules to redirect optical data unit traffic away from the fault on the Ethernet fabric plane.