Slow throughput due to network device or client marking a majority of packets with ECN-Echo
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), 0b11
- 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