37-50
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 37 Configuring Quality of Service
Configuring QoS on Supervisor Engines II-Plus, II+10GE, IV, V, V-10GE, 4924, 4948, and 4948-10GE
This example shows how to configure the DSCP 5 as the default on Fast Ethernet interface 5/24:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface fastethernet 5/24
Switch(config-if)# qos dscp 5
Switch(config-if)# end
Switch#
This example shows how to verify the configuration:
Switch# show qos interface fastethernet 6/1
QoS is enabled globally
Port QoS is enabled
Port Trust State:CoS
Default DSCP:0 Default CoS:0
Tx-Queue Bandwidth ShapeRate Priority QueueSize
(bps) (bps) (packets)
1 31250000 disabled N/A 240
2 31250000 disabled N/A 240
3 31250000 disabled normal 240
4 31250000 disabled N/A 240
Switch#
Configuring Transmit Queues
The following sections describe how to configure transmit queues:
• Mapping DSCP Values to Specific Transmit Queues, page 37-51
• Allocating Bandwidth Among Transmit Queues, page 37-51
• Configuring Traffic Shaping of Transmit Queues, page 37-52
• Configuring a High Priority Transmit Queue, page 37-53
Depending on the complexity of your network and your QoS solution, you might need to perform all of
the procedures in the following sections. However, you will first need to answer the following questions:
• Which packets are assigned (by DSCP value) to each queue?
• What is the size of a transmit queue relative to other queues for a given port?
• How much of the available bandwidth is allotted to each queue?
• What is the maximum rate and burst of traffic that can be transmitted out of each transmit queue?
Independent of the QoS state of an interface, a switch ensures that all the transmit queues are enabled.
Because the DSCP values are trusted by default, a switch uses the appropriate transmit queues based on
the DSCP to map them. This queue selection is based on the internal DSCP to transmit queue mapping
table.