During the deployment of the OptiX OSN equipment, two rings are isolated from each other, but the ECC communication is available between the two rings. Check the relevant information. It is found that the extended ECC function is automatically enabled. Hence, to isolated two rings, you need to disable the extended ECC function.
Product

OptiX OSN 3500
Fault Type

DCN fault
Symptom

The OptiX OSN 3500 forms two rings: north ring and south ring. The two rings are isolated from each other. The north and south rings are connected to the NMS in the central equipment room through a hub for centralized monitoring. Check the ECC routing of the NE. It is found that the ECC routes between the north ring and the south ring are abnormally available.
Cause Analysis

The possible causes are as follows:
The fiber connection between the north ring and the south ring in the central equipment room is incorrect. For example, the fibers of the south ring are connected to the north ring.
The extended ECC function is automatically enabled.
Procedure

Disable the laser by using the T2000. It is found that the fiber connection on the north and south rings is correct.
Check the ECC routing. The OptiX OSN equipment is newly deployed. Thus, the extended ECC function is not preset and is in the default mode. That is, the AUX board automatically enables the extended ECC function. Disable the extended ECC function. It is found that the ECC communication between the north and south rings is unavailable.
Reference Information

When the OSI protocol is started at the network interfaces, the ECC communication is available between isolated subnetworks. For details, see MC-B9 Fibers Are Not Connected Between Equipment but ECC Communication Between Equipment Is Available.