Reasons for communication interruptions between a device and DCN after a WDM hub is connected to a DCN

Question:
The communication between a BWS 1600G device and DCN is interrupted after the hub of the BWS 1600G device is connected to the DCN using two network cables.
The BWS 1600G device uses three subracks, and the ETH indicator on the system control board is steady on.
After a computer is connected to the hub, the computer crashes, causing an NE login failure.
Analysis:
Other ports on the switches in the DCN work properly. Disconnect the network cable from the faulty NE, and then connect the network cable to a normal port. The issue is replicated, the fault is not caused by the switches.
Set the IP address of the computer to the same as that of the device. Test the two network cables connected to the hub respectively. No abnormality occurs, indicating that the fault is not caused by the network cables and IP address configuration.
Check and find that the hub is connected to the DCN using two network cables. This indicates that a loop is formed in the DCN. In this case, the computer is connected to the hub using a network cable, and the CPU usage reaches 99%. As a result, the computer crashes, the indicator of the network interface card (NIC) is steady on, and the ETH indicator of the system control board on the WDM device is also steady on. This indicates that the DCN receives a large volume of data send by itself. As a result, the communication between the NE and DCN is interrupted. Remove one network cable between the hub and DCN. The computer works normally again. In addition, reset the system control board, and then the NE can be logged in to normally.
Root cause:
The main reasons for DCN network interruptions are as follows:
1. Issues of switches in the DCNs
2. Issues of network cables
3. Issues of IP configurations
4. Issues of the hub
Answer:
Remove one network cable between the hub and DCN, and then reset the system control board.
Suggestion and conclusion:
None

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