Overview Of Multiple Qos Policy Support - Cisco ASR 9000 Series Configuration Manual

Overview of Multiple QoS Policy Support

Overview of Multiple QoS Policy Support
In Cisco Common Classification Policy Language (C3PL), the order of precedence of a class in a policy is
based on the position of the class in the policy, that is, the class-map configuration which appears first in a
policy-map has higher precedence. Also, the actions to be performed by the classified traffic are defined inline
rather than using action templates. As a result of these two characteristics, aggregated actions cannot be applied
to traffic that matches different classes.
In order to overcome this limitation, the "Multiple QoS Policy Support" feature is introduced. This feature
enables the users to apply aggregated actions to various classes of traffic and apply multiple QoS policies on
an interface.
Use Case — Multiple QoS Policy Support
Consider a scenario where:
• The classification rules must be applied at different precedence levels.
• Each classification rule must be associated with non-queueing actions (that is, policing/marking).
• Multiple classification rules at different precedence levels must be mapped to a traffic-class.
• Each traffic-class or a group of traffic-classes must be associated with a single queue.
The figure below provides a detailed explanation of the above explained scenario—
In this example, if the traffic packet matches 2.2.2.10 or 1.1.1.0/24, then the traffic packet is forwarded to the
queue that is associated with traffic-class 1. And if the traffic packet matches 1.1.1.10 or 2.2.2.0/24, then the
traffic packet is forwarded to the queue that is associated with traffic class 2.
With the existing Modular Quality of Service, we have the following limitations in order to achieve the above
mentioned requirement—
1 Packets are matched in the order of precedence that is defined based on the position of the class-maps.
There is no way to explicitly specify precedence for a class-map.
2 A queuing action under a class-map in a policy-map, creates a queue for that class.
3 Queues cannot be shared across class-maps.
These limitations can be overcome by separating classification from queuing. By doing this, it is possible to
reorder the class-map from higher precedence to lower precedence and also share queues with multiple
class-maps.
The example below depicts the implementation—
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
156
Configuring Modular QoS Service Packet Classification