Reference Guide

qos-policy-output
2. After you configure an output QoS policy, do one or more of the following:
Strict-Priority Queuing
Configuring Policy-Based Rate Shaping
Allocating Bandwidth to Queue
Specifying WRED Drop Precedence
Strict-Priority Queuing
You can configure strict-priority queueing in an output QoS policy. Strict-priority means that the system de-queues all packets
from the assigned queue before servicing any other queues.
Strict-priority queueing is performed using the Scheduler Strict feature. When scheduler strict is applied to multiple queues, the
higher queue number takes precedence. For more information, see Enabling Strict-Priority Queueing.
Configuring Policy-Based Rate Shaping
To configure policy-based rate-shaping, use the rate-shape command.
● Configure rate-shaping on egress traffic.
QOS-POLICY-OUT mode
rate-shape {kbps | pps} peak-rate {burst-kbps | burst-packets} [committed {kbps | pps}
committed-rate {burst-kbps | burst-packets}]
In a QoS output policy, you can configure rate-shaping on egress traffic:
● In either kilobits per second (kbps) or packets per second (pps)
● By specifying peak rate and the peak burst, and (optionally) committed rate and committed burst size
You must configure the peak rate and peak burst size using the same value: kilobits or packets per second. Similarly, you must
configure the committed rate and committed burst size with the same measurement.
Peak rate refers to the maximum rate for traffic arriving or exiting an interface under normal traffic conditions. Peak burst size
indicates the maximum size of unused peak bandwidth that is aggregated. This aggregated bandwidth enables brief durations of
burst traffic that exceeds the peak rate and committed burst.
Committed rate refers to the guaranteed bandwidth for traffic entering or leaving the interface under normal network
conditions. When traffic propagates at an average rate that is less than or equal to the committed rate, it is considered to be
green-colored or coded. When the transmitted traffic falls below the committed rate, the bandwidth, which is not used by any
traffic that is traversing the network, is aggregated to form the committed burst size. Traffic is considered to be green-colored
up to the point at which the unused bandwidth does not exceed the committed burst size.
Allocating Bandwidth to Queue
The switch schedules packets for egress based on Deficit Round Robin (DRR). This strategy offers a guaranteed data rate.
Allocate bandwidth to queues only in terms of percentage in 4-queue and 8-queue systems. The following table shows the
default bandwidth percentage for each queue.
Table 51. Default Bandwidth Weights
Queue Default Bandwidth Percentage for 4–
Queue System
Default Bandwidth Percentage for 8–
Queue System
0 6.67% 1%
1 13.33% 2%
2 26.67% 3%
3 53.33% 4%
4 — 5%
5 — 10%
Quality of Service (QoS) 611