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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 37 Configuring Quality of Service
Configuring QoS on Supervisor Engine 6-E, Supervisor Engine 6L-E, Catalyst 4900M, and Catalyst 4948E
Dynamic resizing of queues (queue limit class-map action) is supported using the use of the queue-limit
command. Based on the chassis and line card type, all eight queues on a port are configured with equal
queue size.
Shaping
Shaping enables you to delay out-of-profile packets in queues so that they conform to a specified profile.
Shaping is distinct from policing. Policing drops packets that exceed a configured threshold. Shaping
buffers packets so that traffic remains within a given threshold and offers greater smoothness in handling
traffic than policing. You enable average-rate traffic shaping on a traffic class with the policy map class
configuration command.
Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and Supervisor Engine 6L-E support a range
of 32 kbps to 10 gbps for shaping, with a precision of approximately with a precision of approximately
+/- 0.75 percent.
When a queuing class is configured without any explicit shape configuration, the queue shape is set to
the link rate.
To configure class-level shaping in a service policy, perform this task:
Command Purpose
Step 1
Switch# configure terminal
Enters global configuration mode.
Step 2
Switch(config)# policy-map
policy-map-name
Creates a policy map by entering the policy-map name, and enters
policy-map configuration mode.
By default, no policy maps are defined.
Step 3
Switch(config-pmap)# class class-name
Specifies the name of the class whose traffic policy you want to
create or change, and enters policy-map class configuration mode.
By default, no traffic classes are defined.
Step 4
Switch(config-pmap-class)# shape
average {cir-bps kbps | percent
percent}
Enables average-rate traffic shaping.
You can specify the bandwidth in kbps or as a percentage:
• For cir-bps, specify the committed information rate, the bit rate
that traffic is shaped to, in bps. The range is 32000 to
10000000000 bps.
• For percent, specify the percentage of link rate to shape the class
of traffic. The range is 1 to 100.
By default, average-rate traffic shaping is disabled.
Step 5
Switch(config-pmap-class)# exit
Returns to policy-map configuration mode.
Step 6
Switch(config-pmap)# exit
Returns to global configuration mode.
Step 7
Switch(config)# interface interface-id
Specifies a physical port and enter interface configuration mode.
Step 8
Switch(config-interface)#
service-policy output policy-map-name
Specifies the policy-map name, and apply it a physical interface.
Step 9
Switch(config-interface)# end
Returns to privileged EXEC mode.
