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Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-09
Chapter 29 Configuring QoS
Configuring Standard QoS
To disable WRED, use the no wrr-queue random-detect max-threshold queue-id interface
configuration command. To return to the default DSCP-to-threshold map, use the no wrr-queue
dscp-map [threshold-id] interface configuration command.
This example shows how to configure the WRED queue threshold values for queue 1 to 50 percent
and 100 percent, for queue 2 to 70 percent and 100 percent, for queue 3 to 50 percent and 100 percent,
and for queue 4 to 70 percent and 100 percent on the egress interface (Gigabit Ethernet 0/1). The ingress
interface (Gigabit Ethernet 0/2) is configured to trust the DSCP in the incoming packets, to map DSCPs
0, 8, 16, 24, 32, 40, 48, and 56 to threshold 1, and to map DSCPs 10, 20, 30, 40, 50, and 60 to threshold 2.
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# wrr-queue random-detect max-threshold 1 50 100
Switch(config-if)# wrr-queue random-detect max-threshold 2 70 100
Switch(config-if)# wrr-queue random-detect max-threshold 3 50 100
Switch(config-if)# wrr-queue random-detect max-threshold 4 70 100
Switch(config-if)# exit
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# mls qos trust dscp
Switch(config-if)# wrr-queue dscp-map 1 0 8 16 24 32 40 48 56
Switch(config-if)# wrr-queue dscp-map 2 10 20 30 40 50 60
As a result of this configuration, when the queues 1 and 3 are filled above 50 percent, packets with
DSCPs 0, 8, 16, 24, 32, 40, 48, and 56 are randomly dropped. The same packets are randomly dropped
when queues 2 and 4 are filled above 70 percent. When the second threshold (100 percent) is exceeded,
all queues randomly drop packets with DSCPs 10, 20, 30, 40, 50, and 60.
Configuring the Egress Expedite Queue
You can ensure that certain packets have priority over all others by queuing them in the egress expedite
queue. WRR services this queue until it is empty before servicing the other queues.
Beginning in privileged EXEC mode, follow these steps to enable the egress expedite queue:
Step 8
show running-config
or
show mls qos interface interface-id
queueing
Verify the DSCP-to-threshold map.
Step 9
show mls qos interface buffers
Verify the thresholds.
Step 10
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Command
Purpose
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
mls qos
Enable QoS on the switch.
Step 3
interface interface-id
Enter interface configuration mode, and specify the egress
Gigabit-capable Ethernet interface.