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Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
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Chapter 36 Configuring QoS
Configuring Standard QoS
Configuring SRR Shared Weights on Egress Queues
In shared mode, the queues share the bandwidth among them according to the configured weights. The
bandwidth is guaranteed at this level but not limited to it. For example, if a queue empties and does not
require a share of the link, the remaining queues can expand into the unused bandwidth and share it
among them. With sharing, the ratio of the weights controls the frequency of dequeuing; the absolute
values are meaningless.
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.
Beginning in privileged EXEC mode, follow these steps to assign the shared weights and to enable
bandwidth sharing on the four egress queues mapped to a port. This procedure is optional.
To return to the default setting, use the no srr-queue bandwidth share interface configuration
command.
This example shows how to configure the weight ratio of the SRR scheduler running on an egress port.
Four queues are used, and the bandwidth ratio allocated for each queue in shared mode is 1/(1+2+3+4),
2/(1+2+3+4), 3/(1+2+3+4), and 4/(1+2+3+4), which is 10 percent, 20 percent, 30 percent, and 40
percent for queues 1, 2, 3, and 4. This means that queue 4 has four times the bandwidth of queue 1, twice
the bandwidth of queue 2, and one-and-a-third times the bandwidth of queue 3.
Switch(config)#
interface gigabitethernet2/0/1
Switch(config-if)#
srr-queue bandwidth share 1 2 3 4
Configuring the Egress Expedite Queue
You can ensure that certain packets have priority over all others by queuing them in the egress expedite
queue. SRR services this queue until it is empty before servicing the other queues.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the port of the outbound traffic, and enter interface configuration
mode.
Step 3
srr-queue bandwidth share weight1
weight2 weight3 weight4
Assign SRR weights to the egress queues.
By default, all four weights are 25 (1/4 of the bandwidth is allocated to
each queue).
For weight1 weight2 weight3 weight4, enter the weights to control the
ratio of the frequency in which the SRR scheduler sends packets. Separate
each value with a space. The range is 1 to 255.
Step 4
end
Return to privileged EXEC mode.
Step 5
show mls qos interface interface-id
queueing
Verify your entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
