Cisco Catalyst 3560-X Series, Software Configuration Manual

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring QoS
Configuring Standard QoS
These sections contain this configuration information:
• Configuration Guidelines, page 1-84
•
Allocating Buffer Space to and Setting WTD Thresholds for an Egress Queue-Set, page 1-84
(optional)
• Mapping DSCP or CoS Values to an Egress Queue and to a Threshold ID, page 1-86 (optional)
•
Configuring SRR Shaped Weights on Egress Queues, page 1-88 (optional)
• Configuring SRR Shared Weights on Egress Queues, page 1-89 (optional)
•
Configuring the Egress Expedite Queue, page 1-89 (optional)
• Limiting the Bandwidth on an Egress Interface, page 1-90 (optional)
Configuration Guidelines
Follow these guidelines when the expedite queue is enabled or the egress queues are serviced based on
their SRR weights:
• 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.
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
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 buffers, 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.
Note
The egress queue default settings are suitable for most situations. You should change them only when
you have a thorough understanding of the egress queues and if these settings do not meet your QoS
solution.