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CPU congestion observed when huge amount of L3 traffic destined to a network for which no route is present

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TitleCPU congestion observed when huge amount of L3 traffic destined to a network for which no route is present
Symptoms
Bcmrx high CPU utilization noticed.
High CPU congestion observed in the command "debug hal show congestion"

 
Environment
Exos All
Blackdiamond and Summit switches.

 
Cause
In the L3 traffic, the destination mac-address will be that of the switch mac-address when this switch does the inter-vlan routing.
If the destination network is not learnt by this switch, there will not be hardware forwarding of this traffic.
So, the traffic will be lifted to the CPU since the destination mac address is that of the switch mac address.
It will then be discarded by the switch as there is no route.
However, this would already cause a CPU congestion when it is lifted to the CPU when there is huge amount of L3 traffic coming into the switch.
Resolution
This behaviour is expected. We need to make sure that the route is  properly learnt or the traffic to the unknown destination network should be stopped in the network.
Additional notes
Please refer the article below for more scenarios that could result in  the CPU congestion.
Why is process bcmRX going high?
 

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