STP BPDU Kills CPU on Cisco 7609

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Dec 14th, 2008
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Cisco 7600 is connected with routed port on OSM module to a switch. Network behind the switch experiences L2 loop and STP goes crazy. This kills CPU on Cisco 7600. I would like to know is there a mechanism to prevent this behavior. How does Cisco 7600 treat STP BPDU that comes in on a routed port?

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Giuseppe Larosa Mon, 12/15/2008 - 01:38
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Hello Davor,

on a routed port STP BPDUs should be ignored.

But in your case the C7600 cpu goes high and STP is among the processes using more cpu if I understood correctly your post.

I suppose you have checked this with

sh proc cpu sorted

During the L2 loop there are also an high level of broadcast frames ?

Hope to help


djankovic Mon, 12/15/2008 - 01:51
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Well, I didn't have access to the box at the time of problem. All I could see was output from #sh proc cpu history and the fact that all routing protocol adjacencies were broken at that time. I'm not 100% sure what happened but I know that there was stp loop on that side. I wouldn't count that there were a lot of broadcast frames because there is only one other host on this Vlan.


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