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Cisco switches blinking extremely fast

we installed new switches around 4 months ago. we have several locations all conected by fiber. before if we got a loopback the switches would blink super fast and eventually quit responding at the remote location(cisco 2950s). now we have upgraded and have been running fine until 3 days ago, the network has slowed down but still works fine. all the switches seem to be blinking insanely fast like if we had a loopback in the past. not for sure what cisco commands are what to try to narrow it down. is there something to look for or try? any help would be great

damalano

do a sh int status on the switches and look for extreme high use of ports.
blink super fast is relative. are they all blinking at the same time or port by port

Les Moore

Check "show proc cpu hist" and see if the CPU is spiking.
Sounds like Spanning tree gone crazy.
Try enabling multicast storm control on uplink ports of one switch and see if it settles down, then work your way back from there, enabling storm control on each uplink. Then you can check the storm control stats to try to pinpoint the source.

Caoilte

You can try a few things.

Sh spanning-tree root will show you if something "out there" on the network has taken over spanning-tree functions from the root

Sh cdp nei (detail) will let you see if you have a loop on a switch.

Spanning-tree loopguard could be worth putting onto your bas config to allow the switches to err-disable any looped ports.

wavetech

ASKER

the lights are blinking fastly all at the same time. sorry i am a cisco begginer. what am i looking for when i do the spanning-tree root. i assume when i do the sh cdp nei it will show the switch i am on if it has a loopback. i know im over my head but trying to learn. thanks again for the help.

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Caoilte

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wavetech

ASKER

thank you. i found the loopback.