Troubleshooting for port loopback of Cisco switches

Once a department in the company is unable to access the Internet, the Network Manager checks and finds that the Department's dummies are connected 2918 Vswitch Port Fa0/3 It is gray. So we can conclude that the port has Down Drop. Log on 2918 Switch, analyze the problem:

1View the port status and find5Port (for exampleErr-DisabledStatus

Back_building # Show interface status

2, Check the statusErr-DisabledPort information,DownThe reason for dropping is Loopback

Back_building # Show interfaces status err-Disabled

Port name Status reason err-disabled VLANs

Fa0/3 err-disabled loopback

3, SettingsErr-DisableTimeout time. Default Value:300Seconds

Back_building # configure Terminal

Back_building (config) # errdisable recovery interval 10

4, RecoveryErr-DisabledPort

Back_building # configure Terminal

Back_building (config) # errdisable recovery cause loopback

 

After the restoration Fa0/3 There are still problems. Others 4 Ports have been OK , OK Fa0/3" Separate " Exist Loopback , You can conclude that yes Fa0/3 The following fool switch loopback!

Remove2918All other network cables outside the main line are unplugged and restored successfully.Fa0/3Port. Then insert the relevant network cable one by one to determine the network cable with a loop: On the dumb switch, a network cable is directly connected to the dumb switch.2Network adapters!

Troubleshooting.