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24-22
Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 24 Configuring QoS
Understanding QoS
• When you use the bandwidth policy-map class configuration command to configure a class of
traffic as a percentage of total bandwidth, it represents the portion of the excess bandwidth of the
port that is allocated to the class. This means that the class is allocated bandwidth only if there is
excess bandwidth on the port, and if there is no minimum bandwidth guarantee for this traffic class.
Note You can configure bandwidth as percentage of remaining bandwidth only when strict priority
(priority without police) is configured for another class in the output policy map.
Note You cannot configure bandwidth and traffic shaping (shape average) or priority queuing (priority) for
the same class in an output policy map.
This example shows how the classes outclass1, outclass2, and outclass3 and class-default get a
minimum of 40%, 20%, 10%, and 10% of the total bandwidth. Any excess bandwidth is divided among
the classes in the same proportion as rated in the CIR.
Router(config)# policy-map out-policy
Router(config-pmap)# class outclass1
Router(config-pmap-c)# bandwidth percent 40
Router(config-pmap-c)# exit
Router(config-pmap)# class outclass2
Router(config-pmap-c)# bandwidth percent 20
Router(config-pmap-c)# exit
Router(config-pmap)# class outclass3
Router(config-pmap-c)# bandwidth percent 10
Router(config-pmap-c)# exit
Router(config-pmap)# class class-default
Router(config-pmap-c)# bandwidth percent 10
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
Note When you configure CIR bandwidth for a class as a percentage of the total bandwidth, any excess
bandwidth remaining after servicing the CIR of all the classes in the policy map, is divided among the
classes in the same proportion as the CIR rates. If the CIR rate of a class is configured as 0, that class is
also not eligible for any excess bandwidth and as a result receives no bandwidth.
This example shows how to allocate the excess bandwidth among queues by configuring bandwidth for
a traffic class as a percentage of remaining bandwidth. The class outclass1 is given priority queue
treatment. The other classes are configured to get percentages of the excess bandwidth if any, after
servicing the priority queue; outclass2 is configured to get 20 percent, outclass3 to get 30 percent, and
the class class-default to get the remaining 50 percent.
Router(config)# policy-map out-policy
Router(config-pmap)# class outclass1
Router(config-pmap-c)# priority
Router(config-pmap-c)# exit
Router(config-pmap)# class outclass2
Router(config-pmap-c)# bandwidth remaining percent 20
Router(config-pmap-c)# exit
Router(config-pmap)# class outclass3
Router(config-pmap-c)# bandwidth remaining percent 30
Router(config-pmap-c)# exit
Router(config-pmap)# exit