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port being error disabled

Using a Cisco Catalyst 2960-24TC. Port 11 is connected to a data archiving device (10Base-T, custom interface, no manual) used to record all network traffic, then broadcast that data during playback. The archiver records, but upon playback 1 or 2 UDP mesages are broadcast before the port is error disabled. Network Assistant logs the following:

Severity Timestamp Event Description

3-Error Oct 31 21:32:02 Interface GigabitEthernet0/11 - changed state to down

5-Notification Oct 31 21:32:01 Line protocol on Interface GigabitEthernet0/11 - changed state to down

3-Error Oct 31 21:32:00 Loop-back detected on GigabitEthernet0/11.

4-Warning Oct 31 21:32:00 loopback error detected on Gi0/11 putting Gi0/11 in err-disable state

7-Debugging Oct 31 21:31:55 Received 802.1Q BPDU on non trunk GigabitEthernet0/11 VLAN1.

7-Debugging Oct 31 21:31:55 Blocking GigabitEthernet0/11 on VLAN0001. Inconsistent port type.

What can I do to prevent this from happening?


Re: port being error disabled

Hi Umbuttu,

the log clearly tells that an Loop has been formed, possibile reasons that 2 connections might have been given to the same switch which caused a loop on the network, to avoid this, cisco switches will disable the port("error disabled")automatically for avoiding loop on the entire network.


switch A -----> switch B

switch A -----> switch C

switch A -----> switch D

switch A -----> switch B

YES ofcourse, you can connect the cable twice by doing etherchanneling, without that configuration a loop might form on the network, to avoid this loop, cisco makes the port disable.

what you do is, if all of your switches are Cisco, then what you can do is, juz type "show cdp neighbhours" so that you can easily find out whether the same switch is connected twice. if you find, juz remove 1 cable.

hope this helps.

rate this post if cleared, if not please lemme know about that.

Cisco Employee

Re: port being error disabled

Hi Umbutu,

I believe gig0/11 is not a trunk interface? Can you please confirm the "sh run int gig0/11"?

Also if you have not configured switchport mode access, I will recommed you to configure switchport mode access if you do not want this port to be a trunk port.



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