Multiple Interfaces Flapping Repeatedly

[chpmotry]

Hi everyone,  

I’m experiencing a strange issue on one of our Cisco switches: several interfaces (e.g., `GigabitEthernet2/0/5`, `2/0/9`, `2/0/11`, `2/0/13`, `2/0/14`, etc.) are continuously going **up and down every few seconds**.  

I dont have any hub switches and loop sources in my network . The below pictures showed all logs in this switch .The system log is full of messages such as:  

%LINK-3-UPDOWN: Interface GigabitEthernet2/0/9, changed state to down  

%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/9, changed state to up 

This flapping affects multiple ports simultaneously.  

No recent configuration changes were made, and all connected devices appear physically fine (no obvious cable issues).  

**Has anyone have solution for this problem?

Thanks in advance!  

[Mark Elsen]

  - @chpmotry      You should try to capture network traffic at a central point and look for irregular network use
                             such as a broadcast storm or something else.
                            + Use a central syslog server on all switches to forward logging too, then examine those
                               on the syslog server and look for issues , if any.

   M.

[chpmotry]

This vlan 41 in all my network only used in this switch . 

This problem occurs even during hours when no users are active on the systems. However, we also replaced the Windows clients to ensure that there were no computer viruses on the clients.

But there was no improvement.

[Mark Elsen]

  - @chpmotry          Still you need to acquire and install a tool for permanent network traffic monitoring and analysis

  M.

[chpmotry]

What tools are there specifically for monitoring broadcast storms and unusual traffic?

[Mark Elsen]

  - @chpmotry     For instance :  https://www.paessler.com/home-1

                         Using search engines with the topic will give many others ; or ask your favorite AI engine.
                         I used  MRTG in the past for network traffic monitoring; but it requires lot's of manual configuration

  M.
                         

[Ben Weber]

Hi @chpmotry 

Do you have another switch that you could test with the same configuration? This could be a physical issue with either the hardware, the cabling, or inconsistent power to the switch. 

It may be worth shutting down all flapping interfaces and then slowly bringing them back online to see if the issue is caused by a particular port configuration. 

Also, @Mark Elsen makes an excellent point about using a central network monitoring tool for storing and viewing this data. That will help you correlate the events on a single switch with what is happening network-wide.

[Leo Laohoo]

Is there a VoIP phone around?  Plug that phone between the switch and the downstream client. 

If there is something wrong with the switch, the port will flap.  If there is something wrong with the downstream client the port will stop flapping. 

[Dustin Anderson]

The fact you only seem to be seeing it with switch 2, I would say a software bug, or hardware issue maybe. You could try to move some links to another switch to see if the issue follows. Personally, if you have a window reboot the stack and see if it goes away. If it persists than it could be a hardware failure in the switch. 

[pieterh]

don't forget to check the clients as possible cause
maybe power safe is enabled on the network adapters ?
it is possible the adapter "goes to sleep" and is later enabled again by some background process on the client, which repeats itself

p.s. why are the attached  logs dated "jan 9" ?
do you have any recent logs?