Cisco Systems 3750E manual Configuring SRR Shared Weights on Egress Queues, 36-79

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.

	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	Assign SRR weights to the egress queues.
	weight2 weight3 weight4	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	Verify your entries.
	queueing
Step 6
	copy running-config startup-config	(Optional) Save your entries in the configuration file.

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.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		36-79