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Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 24 Configuring QoS
Understanding QoS
Note Effective with Cisco IOS Release 15.2(2)SNI, the lower limit of the committed burst size (bc) is 1 ms.
Class-Based Shaping
Class-based shaping uses the shape average policy-map class configuration command to limit the rate
of data transmission as the number of bits per second to be used for the committed information rate for
a class of traffic. The router supports separate queues for three classes of traffic. The fourth queue is
always the default queue for class class-default, unclassified traffic.
Note In the Cisco ASR 901 router, configuring traffic shaping automatically sets the minimum bandwidth
guarantee or committed information rate (CIR) of the queue to the same value as the PIR.
This example shows how to configure traffic shaping for outgoing traffic on a gigabitethernet port so that
outclass1, outclass2, and outclass3 get a maximum of 50, 20, and 10 Mbps, respectively, of the available
port bandwidth. The class class-default at a minimum gets the remaining bandwidth.
Router(config)# policy-map out-policy
Router(config-pmap)# class classout1
Router(config-pmap-c)# shape average 50000000
Router(config-pmap-c)# exit
Router(config-pmap)# class classout2
Router(config-pmap-c)# shape average 20000000
Router(config-pmap-c)# exit
Router(config-pmap)# class classout3
Router(config-pmap-c)# shape average 10000000
Router(config-pmap-c)# exit
Router(config-pmap)# exit
Router(config)# interface gigabitethernet 0/1
Router(config-if)# service-policy output out-policy
Router(config-if)# exit
Port Shaping
To configure port shaping (a transmit port shaper), create a policy map that contains only a default class,
and use the shape average command to specify the maximum bandwidth for a port.
This example shows how to configure a policy map that shapes a port to 90 Mbps, allocated according
to the out-policy policy map configured in the previous example. The service-policy policy map class
command is used to create a child policy to the parent:
Router(config)# policy-map out-policy-parent
Router(config-pmap)# class class-default
Router(config-pmap-c)# shape average 90000000
Router(config-pmap-c)# service-policy out-policy
Router(config-pmap-c)# exit
Router(config-pmap)# exit
Router(config)# interface gigabitethernet0/1
Router(config-if)# service-policy output out-policy-parent
Router(config-if)# exit
Parent-Child Hierarchy
The router also supports parent policy levels and child policy levels for traffic shaping. The QoS
parent-child structure is used for specific purposes where a child policy is referenced in a parent policy
to provide additional control of a specific traffic type.