Users Guide

● Destination MAC address—6 bytes
● Source MAC address—6 bytes
● Ethernet type/length—2 bytes
● Payload—variable
● Cyclic redundancy check—4 bytes
● Inter-frame gap—variable
The rate adjustment feature is disabled by default. To enable rate adjustment, use the qos-rate-adjust
value_of_rate_adjust command. For example:
qos-rate-adjust 8
If you have configured WDRR and shaping on a particular queue, the queue can become congested. You should configure the
QoS rate adjust value considering the overhead field size to avoid traffic drops on uncongested queues.
If you have multiple streams within a queue, you must find the overhead size for the different streams and the QoS rate adjust
value should be the highest overhead size from among the various streams within that queue.
Consider the example where you have configured WDRR and shaping on a queue that has two different traffic streams, TS1 and
TS2, that uses preamble, SFD, and IFG overhead fields:
● If the IFG in TS1 uses 16 bytes, QoS rate adjust value should be 24 (preamble + SFD requires 8 bytes and IFG 16 bytes).
● If the IFG in TS2 uses 12 bytes, QoS rate adjust value should be 20 (preamble + SFD requires 8 bytes and IFG 12 bytes).
In this case, the highest QoS rate adjust value between the two streams is 24 bytes. Hence, you must configure the QoS rate
adjust value as 24.
NOTE: This feature is not supported on the S4200-ON Series platforms.
Configure quality of service
Configuring QoS is a three-step process:
1. Create class-maps to classify the traffic flows. The following are the different types of class-maps:
● qos (default)—Classifies ingress data traffic.
● queuing—Classifies egress queues.
● control-plane—Classifies control-plane traffic.
● network-qos—Classifies traffic-class IDs for ingress buffer configurations.
● application—Classifies application-type traffic. The reserved policy-map policy-iscsi defines the actions for class-iscsi
traffic.
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Quality of service