Hi, everyone! Today I’m going to introduce what can i do if an ethernet interface frequently alternates between up and down states?
A:An Ethernet interface frequently alternates betweenUp and Down states. The possible causes are as follows:
a. The cable is not properly connected to the interface.
b. The twisted pair or fiber connected to the interface istoo long or the fiber attenuation is high.
c. The local and remote interfaces work at different duplexmodes , speeds, negotiation modes.
d. The local and remote interfaces, interface modules, ordevices are faulty.
Procedure
Step 1 Check whether the cable and interface modules areproperly installed on the localand remote devices. If the fault persists after the cable and interface modulesare properly installed, go to step 2.
Step 2 Check whether the two interfaces have the same duplex mode, rate, andnegotiation mode. Run thedisplay interfacecommand on the two interfaces to check the rates,duplex modes, and negotiation modes of the interfaces.
If the fault persists, go to step 3.
Step3 Check whether theinterface modules and the link between the interfaces work properly. If the twointerfaces are connected by a twisted pair, check the following items. 
If the two interfaces are connected by fibers,check the following items.
If the fault persists, go to step4.
Step4 Check whether thelocal or remote device has a hardware fault.
Connect the twisted pair or fibers to anotherinterface. If the remote device is a powered device (PD), check whether thepower of the remote device exceeds the maximum power of the interface.
If the fault persists, go to step 5.
Step 5 Check the interface Up/Down log to rectify thefault.
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For details, see the S Series Switches InterfaceTroubleshooting.
Step 1: Log in to the enterprise technical supportwebsite at http://support.huawei.com/enterprise.
Step 2: Click Switches.
Step 3: Click the name of the product to bequeried, for example, S7700.
Step 4: Choose Documentation> S7700 Troubleshooting – Preliminary to find theTroubleshootingfor your switch model. 
Step 5: Open the Troubleshooting.Choose Interface Faults > An Ethernet Interface FrequentlyAlternates Between Up and Down States in the navigation tree on the left,and follow the instructions.
S7700&S9700 Series Switches Troubleshooting -Preliminary
http://support.huawei.com/enterprise/en/doc/EDOC1000027402?idPath=7919710|21782164|21782186|22318632|6805481
This is what I want to talk about/share with you today, thank you!
