An Ethernet Interface Frequently Alternates Between Up and Down States

Fault Description

An Ethernet interface frequently alternates between Up and Down states.

Troubleshooting Procedure

Check whether the interface modules and the link between the interfaces work properly.

If the two devices are connected by a twisted pair, check the following items.

Item	Expected Result	Follow-up Procedure
Twisted pair working status	The tester shows that the twisted pair works properly.	If the twisted pair is faulty, replace it.
Twisted pair length	The twisted pair length is less than 100 m. NOTE: The 10/100/1000M electrical interfaces use RJ45 connectors and Category 5 or higher twisted pairs. The maximum transmission distance of such cables is 100 m.	If the twisted pair length exceeds 100 m, perform either of the following operations: Shorten the distance between the two devices. If the distance between the two devices cannot be shortened, deploy a repeater, hub, or switch between the devices.

If the two devices are connected by optical fibers, check the following items.

Item	Expected Result	Follow-up Procedure
Optical fiber working status	The tester shows that optical signals are sent and received properly. In a loopback test, the two interfaces are Up.	If optical signals cannot be sent or received, replace the optical fibers. If the fault persists, replace the optical modules.
Types of optical modules and optical fibers	The optical fiber type matches the optical module type. For details about mappings between optical modules and optical fibers, see "Pluggable Modules for Interfaces - Important Notes About Using Optical Modules Certified for Huawei Switches" in the Hardware Description of a specified model.	If the optical fiber type does not match the optical module type, replace the optical module or optical fiber.
Optical fiber length and maximum transmission distance of optical modules	The optical fiber length must be shorter than the maximum transmission distance of an optical module. For the maximum transmission distance supported by different optical modules, see "Pluggable Modules for Interfaces - Important Notes About Using Optical Modules Certified for Huawei Switches" in the Hardware Description of a specified model.	If the optical fiber length exceeds the maximum transmission distance of the optical modules, shorten the distance between the devices or use optical modules with a longer transmission distance.
Optical signal attenuation	The tester shows that the optical signal attenuation is in the allowed range. For the attenuation range, see "Pluggable Modules for Interfaces - Important Notes About Using Optical Modules Certified for Huawei Switches" in the Hardware Description of a specified model.	If the attenuation is high, replace the optical fibers. If the fault persists, shorten the distance between the devices and use shorter optical fibers.

If the fault persists, go to step 2.

Check whether the two interfaces have the same duplex mode, rate, and auto-negotiation mode.

Run the display interface command on the two interfaces to check their rates, duplex modes, and auto-negotiation modes.

Item	Description	Follow-up Procedure
Negotiation	Auto-negotiation mode of the interface: ENABLE: indicates that the interface works in auto-negotiation mode. DISABLE: indicates that the interface works in non-auto-negotiation mode.	The two interfaces must work in the same auto-negotiation mode. Run the negotiation auto command in the interface view to configure the interfaces to work in auto-negotiation mode. If the fault persists, configure the interfaces to work in non-auto-negotiation mode and use the same rate and duplex mode.
Speed	Current rate of the interface.	If the rates of the interfaces are different, run the speed command in the interface view to set the same rate on the two interfaces.
Duplex	Duplex mode of the interface.	If the duplex modes of the interfaces are different, run the duplex command in the interface view to set the same duplex mode on the two interfaces.

If the fault persists, go to step 3.

Check the interface Up/Down log information to rectify the fault.

Up/Down Log Information	Possible Cause	Follow-up Procedure
Multiple Up/Down logs are generated on the interface within a short period (60s). The interface instantly alternate between Up and Down states.	The remote device is restarting, so the local interface instantly alternates between Up and Down states for multiple times.	No action is required. Wait until the remote device finishes restarting.
A group of interfaces alternate between Up and Down states simultaneously.	An active/standby switchover is performed on the remote device. When multiple interfaces of the local device connect to the same remote device, the interfaces alternate between Up and Down states simultaneously if an active/standby switchover occurs on the remote device.	No action is required. Wait until the remote device finishes the active/standby switchover.
It takes a long period for the interface to change from Down to Up.	This log information is informational. The remote device performs operations on the local interface.	No action is required.
The Up/Down logs are generated on the interface at different times. In this period, the interface instantly alternates between Up and Down states at an interval smaller than 1s.	The optical module does not match the hardware; the optical module is sensitive to the signal jitter; or the receive optical power is too low. The remote or local interface is faulty. Port protection is configured on the remote device.	Replace the optical module and check whether the optical module or optical fiber is properly connected. Connect the local interface to another remote interface. Disable port protection on the remote device.

If the fault persists, go to step 4.

Check whether the local or remote device has a hardware fault.

Connect the devices using other interfaces.

If the fault persists, go to step 5.
Collect the following information and contact technical support personnel:
- Results of the preceding troubleshooting procedure
- Configuration file, logs, and alarms of the device