Configuring Egress Queue Characteristics; Configuration Guidelines; Allocating Buffer Space To And Setting Wtd Thresholds For An Egress Queue-Set - Cisco WS-C3750-48PS-S Software Configuration Manual

Configuring Standard QoS

Configuring Egress Queue Characteristics

Depending on the complexity of your network and your QoS solution, you might need to perform all of
the tasks in the next sections. You will need to make decisions about these characteristics:
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These sections describe how to configure egress queue characteristics:
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Configuration Guidelines

Follow these guidelines when the expedite queue is enabled or the egress queues are serviced based on
their SRR weights:
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Allocating Buffer Space to and Setting WTD Thresholds for an Egress Queue-Set

You can guarantee the availability of buffers, set WTD thresholds, and configure the maximum memory
allocation for a queue-set by using the mls qos queue-set output qset-id threshold queue-id
drop-threshold1 drop-threshold2 reserved-threshold maximum-threshold global configuration command.
Each threshold value is a percentage of the queue's allocated memory, which you specify by using the
mls qos queue-set output qset-id buffers allocation1 ... allocation4 global configuration command.
The queues use WTD to support distinct drop percentages for different traffic classes.
The egress queue default settings are suitable for most situations. You should change them only when
Note
you have a thorough understanding of the egress queues and if these settings do not meet your QoS
solution.
Catalyst 3750 Switch Software Configuration Guide
32-60
Which packets are mapped by DSCP or CoS value to each queue and threshold ID?
What drop percentage thresholds apply to the queue-set (four egress queues per port), and how much
reserved and maximum memory is needed for the traffic type?
How much of the fixed buffer space is allocated to the queue-set?
Does the bandwidth of the port need to be rate limited?
How often should the egress queues be serviced and which technique (shaped, shared, or both)
should be used?
Configuration Guidelines, page 32-60
Allocating Buffer Space to and Setting WTD Thresholds for an Egress Queue-Set, page 32-60
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Mapping DSCP or CoS Values to an Egress Queue and to a Threshold ID, page 32-62
Configuring SRR Shaped Weights on Egress Queues, page 32-64
Configuring SRR Shared Weights on Egress Queues, page 32-65
Configuring the Egress Expedite Queue, page 32-66
Limiting the Bandwidth on an Egress Interface, page 32-66
If the egress expedite queue is enabled, it overrides the SRR shaped and shared weights for queue 1.
If the egress expedite queue is disabled and the SRR shaped and shared weights are configured, the
shaped mode overrides the shared mode for queue 1, and SRR services this queue in shaped mode.
If the egress expedite queue is disabled and the SRR shaped weights are not configured, SRR
services this queue in shared mode.
Chapter 32
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Configuring QoS
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