Reference Guide

Congure egress buer
Default settings
All port queues are allocated with reserved buers and when the reserved buers are consumed, each queue starts using the shared buer
from the default pool.
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
value 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 Congestion Experienced (CE) bit of ECN eld in a packet as ECN-
capable trac (ECT).
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
Quality of service
679