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S-Series: High CPU (switch packet processing) when a GRE tunnel traverses the switch (source and dest elsewhere) and Vxlan is enabled

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TitleS-Series: High CPU (switch packet processing) when a GRE tunnel traverses the switch (source and dest elsewhere) and Vxlan is enabled
Symptoms
  • High CPU ( Switch Packet Processing task runs up to the max of 60% )
  • Large number of flows on port where GRE tunnel enters the switch ( up to 500,000 )
  • potential dropped frames
Environment
  • S-Series
  • Firmware 8.63.01
  • GRE Tunnel traverses through the switch
  • Vxlan enabled on the switch
Cause
The issue can happen if there is a GRE tunnel traversing the switch toward Purview and a lot of customer traffic mirrored within that tunnel. It may or may not show symptoms dependent on the amount of traffic in the tunnel.

When enabling Vxlan on a chassis this leads to the system (in the background ) enabling parsing of GRE headers and hence creating flows on the port of ingress of the gre tunnel for all the contents of the tunnel where there should just be one flow for the tunnel.

In some environments that may lead negative consequences like exceeding flow limits, high CPU usage, and dropped packets.
Resolution
Upgrade to Firmware 8.63.06

 
Additional notes
See also the following article whic has exactly the same symptoms for a similar reason but with a different root cause and a different fix in fimrware
S-Series: High CPU (switch packet processing) when a GRE tunnel traverses the switch (source and dest elsewhere) and netflow is enabled

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