Dell MX5108n OS10 Enterprise Edition User Guide for PowerEdge MX IO Modules Re - Page 590

You can override the default priority group settings when LLFC or PFC is enabled. 1 Create network-qos type class-map to match the traffic classes. For LLFC match all the traffic classes(0-7) and for PFC, match the required traffic class. OS10(config)# class-map type network-qos tc OS10 (config-cmap-nqos)# match qos-group 0-7 2 Create network-qos type policy-map to define the actions for traffic classes, like buffer configuration and thresholds. OS10(config)# policy-map type network-qos buffer OS10(config-pmap-network-qos)# class tc OS10 (config-pmap-c-nqos)# pause buffer-size 300 pause-threshold 200 resume-threshold 100 OS10 (config-pmap-c-nqos)# queue-limit thresh-mode dynamic 5 Configure egress buffer Default settings All port queues are allocated with reserved buffers and when the reserved buffers are consumed, each queue starts using the shared buffer from the default pool. The reserved buffer per queue is 1664 bytes for the speed of 10G, 25G, 40G, 50G, and 100G. The default dynamic shared buffer threshold value is 8. Configure queue buffer settings 1 Create queuing type class-map to match the queue. OS10(config)# class-map type queuing q1 OS10(config-cmap-queuing)# match queue 1 2 Create queuing type policy-map to define the actions for queues, like buffer configuration and thresholds. OS10(config)# policy-map type queuing q-buffer OS10(config-pmap-queuing)# class q1 OS10(config-pmap-c-que)# queue-limit queue-len 200 thresh-mode dynamic 5 Congestion avoidance Congestion avoidance is a predictive method to anticipate and take necessary action to avoid congestion. The following are the different mechanisms used to avoid congestion: • Tail drop-Packets are buffered at traffic queues. When the buffers are exhausted or reach the configured threshold, excess packets are dropped. By default, OS10 uses tail drop for congestion avoidance. • Random early detection (RED)-In tail drop mechanism, different flows are not considered in buffer utilization. When multiple hosts start retransmission, tail drop causes TCP global re-synchronization. Instead of waiting for the queue to get filled up completely, RED starts dropping excess packets with a certain drop-probability, when the average queue length exceeds the configured minimum threshold. The early drop ensures that only some of TCP sources slow down, which avoids global TCP re-synchronization. • Weighted random early detection (WRED)-This mechanism allows different drop-probabilities and thresholds for each color (red, yellow, green) of traffic. You can configure the drop characteristics for 3 different flows by assigning the colors to the flow. You can assign colors to a particular flow or traffic by various methods, like ingress policing, qos input policy-maps, and so on. • Explicit congestion notification (ECN)-This is an extension of WRED. Instead of dropping the packets when the average queue length crosses the minimum threshold values, ECN marks the CE bit of ECN field in a packet as ECN-capable traffic. Configure congestion avoidance 1 Configure WRED profile in the CONFIGURATION mode. OS10(config)# wred wred_prof_1 2 Configure WRED threshold parameters for different colors in the WRED CONFIGURATION mode. OS10(config-wred)# random-detect color yellow minimum-threshold 100 maximum-threshold 300 drop-probability 40 590 Quality of service