Light blinking on all Cisco equipment simultaneously

Unanswered Question
Mar 23rd, 2007

I have a client where all thier Cisco equipment from the 2811 routers, to the pix, and all the 3500 switches all the lights on the ports are blinking in unisence. Meaning they are all flashing at the same time. I checked and saw that spanning tree is not configured properly. Switch off the core switch is the Root bridge for Vlan 1 and another switch off the core is the root for the rest of the Vlans. I think If i make the Core switch the Root, this might help me find a loop. Have you guys ever seen this before.

Some problems the client is experiencing is Echo on VOIP calls inbound and slow internet on the network certain times. Keep in mind our client also has recently had virus on thier network.

But I am very concerned about the lights flashing the way they are. All flashing at the same time.

I have this problem too.
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Jon Marshall Fri, 03/23/2007 - 15:50


If you suspect a spanning tree issue have you checked the switch logs to see if there are any mac-address flapping messages ?

Attached is a link to a doc on troubleshooting STP problems in your network.

Which switches to use as root and secondary depends on your network topology. Generally you have the most powerful switches in the centre of the switch network fulfilling this function.



Rajat Chauhan Sat, 03/24/2007 - 12:03

Hi Jon,

I seriously expect a virus here. I can say that from my TAC experience. STP design is not bad at all. Its common to have such segregations. Try removing some servers/clients one by one or try to develop some similar approach, i thinks its surely is a virus.

For STP:


Pls rate helpful posts.


Jon Marshall Sat, 03/24/2007 - 17:09

Hi Rachauha

I didn't mean to suggest that there was anything wrong with the STP design. It may well be due to a virus but there are certain things to check to eliminate the possibility of an STP issue.



shirwaziri1_2 Sun, 03/25/2007 - 00:11


Yeah, I wanted to eliminate any unnecessary issues before ruling that it could be the virus. That is why I put it to the form to see if anyone else experience this problem. There is no flapping on any interfaces on any cisco equipment. Tx and Rx loads are well below 255 thresholds. I did see a CPUHOG Logger message in the syslog of the voice switch after I ran a "debug spanning tree all".

I plan to reboot all the cisco equipment maybe to clear the Flashing on the LED's. Would you say this is a troubleshooting step taht would be worth doing. I guess it couldn't hurt.

Jon Marshall Sun, 03/25/2007 - 01:41


debug spanning tree all will have an adverse effect on the CPU but if everything else looks normal it does look as though STP is not the issue.

If you are in a position to reboot as you say it wouldn't hurt although i generally try to avoid this until i have exhausted all the other possibilities.




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