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Slow throughput due to network device or client marking a majority of packets with ECN-Echo

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Category:
ontap-9
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nas
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Applies to

  • ONTAP 9.6+
  • TCP Explicit Congestion Notification (ECN) in use by client/network

Issue

  • Slow throughput/performance, usually on read
  • Possible application layer timeouts reported by clients
  • “netstat -s -p tcp” shows a high number of packets with CE compared to the total packets received: “packets with ECN CE bit set” / “packets received” > 0.005
  • Packet trace shows all or a majority of packet received by a client or ONTAP with the IP ECN field set to “Congestion Expirienced” (CE), 0b11Slow throughput due to network device
  • Packet trace shows all or a majority of packets marked with the “Congestion Window Reduced” (CWR) TCP Flag; Simultaneously, the “Explicit Congestion Expirienced” (ECE) Flag remains set for more than one TCP window Slow throughput due to network device

 

 

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