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New Member

How to reactivate a switch port

My Cisco 3750 switch deactivated a port when I connected a hub because a loop back was detected.

sh interfaces fe 5/0/10 output is:

FastEthernet5/0/10 is down, line protocol is down (err-disabled)

I would like that anybody say me how I can to activate again this port.

Anybody knows how can be the causes of this fact?. The hub is a HP ProCurve.



Re: How to reactivate a switch port

HI Carl, [Pls Rate if HELPS]

I See "err-disabled" message in your Output. I hope Port-Security Feature enabled in the Interface Fe 5/0/10.

#show port-security

command will show help you to identify the Problem. I hope some Mac-address, VLAN, IP-Address has been binded to this Particular port.

Some Violation on this Security Feature (on interface) will make the Interface go into Shutdown State.

You will have to Manually enter the Interface Configuration mode & input "no shut" command in config-if to re-enable the Port to UP status.

To See the Interface is in Shutdown State:

Switch#sh run interface fastEthernet 5/0/10

Also, verify the Security Feature using "Show port-security" command output.


Best Regards,

Guru Prasad R

New Member

Re: How to reactivate a switch port

You didn't help me.

I entered show port-security command and it doesn't help me. Here is the output.

Secure Port MaxSecureAddr CurrentAddr SecurityViolation Security Action

(Count) (Count) (Count)



Total Addresses in System (excluding one mac per port) : 0

Max Addresses limit in System (excluding one mac per port) : 6272

I typed no shut command in the interface config and interface state didn't change.


Re: How to reactivate a switch port


To identfy the problem use:

show interface "type num" statuis err-disable

To enable the port put the port into shutdown state and after it no shutdown.

inteface fastethernet 0/1


no shutdown



Please rate me if I helped.

New Member

Re: How to reactivate a switch port

Your answer don't help me.

I entered no shut and shut commands in the interface and blockade goes on.

Output of show interface fe 5/0/10 don't help me too:

Port Status Reason

Fa5/0/10 err-disabled loopback


Re: How to reactivate a switch port

Don't tell this, since you can see that you have Loopack problem (spanning-tree is enabled on your system, if not redundant L2 path can cause this loopback)



Please rate me if I helped.

New Member

Re: How to reactivate a switch port

Ok, thanks but what would be the way to reactivate thsi port?.

Re: How to reactivate a switch port


Please review this:


Loopback error

A loopback error occurs when the keepalive packet is looped back to the port that sent the keepalive. The switch sends keepalives out all the interfaces by default. A device can loop the packets back to the source interface, which usually occurs because there is a logical loop in the network that the spanning tree has not blocked. The source interface receives the keepalive packet that it sent out, and the switch disables the interface (errdisable). This message occurs because the keepalive packet is looped back to the port that sent the keepalive:

%PM-4-ERR_DISABLE: loopback error detected on Gi4/1, putting Gi4/1 in

err-disable state

Keepalives are sent on all interfaces by default in Cisco IOS Software Release 12.1EA-based software. In Cisco IOS Software Release 12.2SE-based software and later, keepalives are not sent by default on fiber and uplink interfaces. For more information, refer to Cisco bug ID CSCea46385 ( registered customers only) .

The suggested workaround is to disable keepalives and upgrade to Cisco IOS Software Release 12.2SE or later.


Mohammed Mahmoud.

Re: How to reactivate a switch port

hi, in aiddition to great suggestions from all, you need to investigate a bit fruther on whay type or switc/hub you are connecting to your fe5/0/0, and the systems connecting into that hub.

error-disable mechanish was design to provide protection to your network, the last thing you want to have is problems in your network such as bridging loops that may render your network useless. Before desabling these types of protection please read Mohammed's provided link which covers all angles to help you troubleshoot this problem.


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