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switchport shutting down automatically

i have a problem in my base station, the router is connected to a switch and a second switch is connected to the first switch.(with just one cable),i have a client conected to this second switch with a point to point link. the strange thing is that whenever the client restart its router or at any other time, i just find out that the switch port at the base station shut its self down. ie if u do a show run the shutdown will be seen configured. i.e

interface FastEthernet0/3

switchport trunk encapsulation dot1q

switchport trunk native vlan 152

switchport mode trunk


no ip address

no cdp enable

i need help in understanding what is hapening if anybody has experience this before.



Re: switchport shutting down automatically


are you seeing any error logs on your router ?


Community Member

Re: switchport shutting down automatically

the error log on the router on the router are just abt the holding time of the client expiring and wen it comes back up.

this is the log on the switch,

11:25:24: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on FastEthernet0/3.

The port is forced to linkdown.

Re: switchport shutting down automatically


Most probable reason for looping is bad cable.

Do find the messaged obtained from CCO..

%ETHCNTR-3-LOOP_BACK_DETECTED: , Loop-back detected on [chars]. The port is forced to linkdown.

This message means that a loopback condition might be the result of a balun cable incorrectly connected into a port. [chars] is the port.

Recommended Action: On non-PoE switches, check the cables. If a balun cable is connected and the loopback condition is desired, no action is required. Otherwise, connect the correct cable, and then enable the port up by entering the no shutdown interface configuration command.

Also you can refer the below link for more info..


Re: switchport shutting down automatically


A small suggestion:

Please remove the shutdown option from the configuration of the Fa0/3 and save the config, or else in case your Core Switch reboots, the fa0/3 port will come back in Shutdown mode only and you may need to spend some extra time to figure out the cause of the issue.


Wilson Samuel

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