Reference Guide

The reserved buer per queue is 1664 bytes for the speed of 10G, 25G, 40G, 50G, and 100G. The default dynamic shared buer threshold
is 8.
Congure queue buer 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 dene the actions for queues, like buer conguration 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 dierent
mechanisms used to avoid congestion:
• Tail drop—Packets are buered at trac queues. When the buers are exhausted or reach the congured threshold, excess packets
are dropped. By default, OS10 uses tail drop for congestion avoidance.
• Random early detection (RED)—In tail drop mechanism, dierent ows are not considered in buer utilization. When multiple hosts
start retransmission, tail drop causes TCP global re-synchronization. Instead of waiting for the queue to get lled up completely, RED
starts dropping excess packets with a certain drop-probability, when the average queue length exceeds the congured 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 dierent drop-probabilities and thresholds for each color (red,
yellow, green) of trac. You can congure the drop characteristics for 3 dierent ows by assigning the colors to the ow. You can
assign colors to a particular ow or trac by various methods, like ingress policing, qos input policy-maps, and so on.
• Explicit congestion notication (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 eld in a packet as ECN-capable trac.
Congure congestion avoidance
1 Congure WRED prole in the CONFIGURATION mode.
OS10(config)# wred wred_prof_1
2 Congure WRED threshold parameters for dierent colors in the WRED CONFIGURATION mode.
OS10(config-wred)# random-detect color yellow minimum-threshold 100 maximum-threshold 300
drop-probability 40
3 Congure the exponential weight value for the WRED prole in the WRED CONFIGURATION mode.
OS10(config-wred)# random-detect weight 4
4 Enable ECN.
OS10(config-wred)# random-detect ecn
5 Enable WRED/ECN on a queue.
OS10(config)# class-map type queuing c1
OS10(config-cmap-queuing)# match queue 2
OS10(config-cmap-queuing)# exit
OS10(config)# policy-map type queuing p1
OS10(config-pmap-queuing)# class c1
OS10(config-pmap-c-que)# random-detect wred_prof_1
6 Enable WRED/ECN on a port.
OS10(config)# interface ethernet 1/1/1
OS10(conf-if-eth1/1/1)# random-detect wred_prof_1
7 Enable WRED/ECN on a service-pool.
OS10(config)# system qos
OS10(config-sys-qos)# random-detect pool 0 wred_prof_1
Quality of service
563