[c-nsp] cisco-nsp Digest, Vol 40, Issue 59

[Burton, Lowell E. (US - Hermitage)]

On Sat, Mar 18, 2006 at 06:56:30AM -0000, Gangasagar Amula wrote:
>> The below output was captured when we are pinging from one vlan to
other vlan.
>> We have 4006 Switch involved in between.
>> 
>> ----------------------------------------------------------------?
>> 64 bytes from 10.176.0.51: icmp_seq=6 ttl=127 time=26.7 ms (DUP!)
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=11.1 ms
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=11.2 ms (DUP!)
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=11.6 ms (DUP!)
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=11.6 ms (DUP!)
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=12.0 ms (DUP!)
>> 64 bytes from 10.176.0.51: icmp_seq=7 ttl=127 time=12.1 ms (DUP!)
>
>This very much looks like you have a loop in your ethernet topology
>somewhere - ports are connected together that should not be, and for 
>some reason, spanning tree isn't disabling the ports.
>
>> CPU utilization for five seconds:  85.63%
>>                       one minute:  77.70%
>>                     five minutes:  75.19%
>
>As people have suggested in the other thread: most likely the high CPU
>is related to the packet loop.

I have also seen this when a customer accidentally connects multiple
router's interfaces from the same router into the same vlan on a single
layer 2 switch.  For example:

ROUTER1 int fast0/1 ------> SWITCH1 vlan1 int fast1/0/1
ROUTER1 int fast0/2 ------> SWITCH1 vlan1 int fast1/0/3
ROUTER1 int gig0/1 -------> SWITCH1 vlan1 int gig1/0/1 


This message (including any attachments) contains confidential information intended for a specific individual and purpose, and is protected by law.  If you are not the intended recipient, you should delete this message. 


Any disclosure, copying, or distribution of this message, or the taking of any action based on it, is strictly prohibited. [v.E.1]