An Ethernet Interface Is Physically Down

Fault Description

An Ethernet interface is physically Down.

Troubleshooting Procedure

Check whether the devices are powered on, and 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.
Twisted pair type	Twisted pair cables are classified into straight-through cables and crossover cables. A straight-through cable connects Ethernet interfaces between the following devices: A router and a hub A router and an Ethernet switch A computer and an Ethernet switch A computer and a hub A crossover cable connects Ethernet interfaces between the following devices: Two routers A router and a computer Two hubs A hub and a switch Two switches Two computers	If the twisted pair type is incorrect, replace the twisted pair.

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.

Twisted pair type

Twisted pair cables are classified into straight-through cables and crossover cables.

A straight-through cable connects Ethernet interfaces between the following devices:

A router and a hub
A router and an Ethernet switch
A computer and an Ethernet switch
A computer and a hub

A crossover cable connects Ethernet interfaces between the following devices:

Two routers
A router and a computer
Two hubs
A hub and a switch
Two switches
Two computers

If the twisted pair type is incorrect, replace the twisted pair.

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

Item	Expected Result	Follow-up Procedure
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 Hardware Description of a specified model. Determine whether the optical fiber type matches the optical module type according to the following information: A multimode optical fiber can be used together with a multimode optical module. A single-mode optical fiber can only be used with a single-mode optical module. Generally, a single-mode optical fiber is yellow, and a multimode optical fiber is orange. Two connected optical modules must have the same wavelength.	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 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 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.
Optical fiber working status	The tester shows that optical signals are sent and received properly. During a loopback test, an interface is Up when both ends of an optical fiber are connected to the same optical module installed on the interface.	If optical signals cannot be sent or received, replace the optical fibers. If the fault persists, replace the optical modules.

If the fault persists, go to step 2.

Check whether the local and remote interfaces have been manually shut down.

Run the display interface command and check the current state field in the command output. If the current state field is Administratively down, the interfaces are shut down. Run the undo shutdown command on the interfaces.

If the interface is still Down, go to step 3.

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	Interface rate.	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.
Mdi	MDI type of the interface: across: indicates that the interface can use a crossover cable. auto: indicates that the interface automatically identifies the network cable type. That is, the interface can use a straight-through cable or a crossover cable. normal: indicates that the interface can use a straight-through cable.	The two interfaces must support the same MDI type. By default, an interface uses the auto type. If the interfaces do not use this type, run the mdi command to set the MDI type of the interfaces to auto.

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