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Catalyst 3550 Switch ports flashing at same time

what causes ports on a 3550 switch to flash at the same time? when this happens no one is able to use the network and we have to reboot the switch in order to normalize.

4 REPLIES
New Member

Re: Catalyst 3550 Switch ports flashing at same time

We've got 3560 switch and have the same problem sometimes.

I think it happens when there's broadcast or multicast storm but I'm not 100% sure.

If anybody knows answer please post.

Thanks.

Re: Catalyst 3550 Switch ports flashing at same time

HI

Is this switch is having any redundant links.If check for any STP issues.It may cause due to a STP Loop.

Thanks

Mahmood

Re: Catalyst 3550 Switch ports flashing at same time

Best way to determine what is going on is to get a console connection when the problem is occuring and capturing:

show proc cpu >> what is the cpu util?

show spanning summary >> see if the STP root is what it should be.

show log >> look for any clues that will explain the cpu or STP.

show spanning-tree vlan x >> for each vlan.

if possible, disconnect the links one at a time, if you suspect a loop, start with uplinks or link connecting to another switch. Once connectivity is restore as soon as a particular link is severed, note what is connected on that link and reconnect the rest of the link one at a time to verify that the issue is gone. The next step would be to investigate why that particular switch is causing a loop.

New Member

Re: Catalyst 3550 Switch ports flashing at same time

thank you very much for all your useful suggestions and pointers. appreciate the quick response too.

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