Prerequisites For Configuring Modular Qos Packet Classification On Cisco Asr 9000 Series Routers; Information About Configuring Modular Qos Packet Classification On Cisco Asr 9000 Series Routers; Packet Classification Overview - Cisco ASR 9000 Series Configuration Manual

Prerequisites for Configuring Modular QoS Packet Classification on Cisco ASR 9000 Series Routers

Prerequisites for Configuring Modular QoS Packet
Classification on Cisco ASR 9000 Series Routers
The following prerequisites are required for configuring modular QoS packet classification on your
network:
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Information About Configuring Modular QoS Packet
Classification on Cisco ASR 9000 Series Routers
To implement QoS packet classification features in this document, you must understand the following
concepts:
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Packet Classification Overview

Packet classification involves categorizing a packet within a specific group (or class) and assigning it a
traffic descriptor to make it accessible for QoS handling on the network. The traffic descriptor contains
information about the forwarding treatment (quality of service) that the packet should receive. Using
packet classification, you can partition network traffic into multiple priority levels or classes of service.
The source agrees to adhere to the contracted terms and the network promises a quality of service. Traffic
policers and traffic shapers use the traffic descriptor of a packet to ensure adherence to the contract.
Traffic policers and traffic shapers rely on packet classification features, such as IP precedence, to select
packets (or traffic flows) traversing a router or interface for different types of QoS service. For example,
by using the three precedence bits in the type of service (ToS) field of the IP packet header, you can
categorize packets into a limited set of up to eight traffic classes. After you classify packets, you can use
other QoS features to assign the appropriate traffic handling policies including congestion management,
bandwidth allocation, and delay bounds for each traffic class.
On Cisco IOS XR software, methods of classification may consist of the logical combination of any
fields in the packet header, where a packet header may be a Layer 2, a Layer 3, or a Layer 4 header; or
classification based on the incoming or outgoing physical or virtual interface.
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-8
Configuring Modular Quality of Service Packet Classification on Cisco ASR 9000 Series Routers
D r a f t — C i s c o C o n f i d e n t i a l
You must be in a user group associated with a task group that includes the proper task IDs. The
command reference guides include the task IDs required for each command. If you suspect user
group assignment is preventing you from using a command, contact your AAA administrator for
assistance.
You must be familiar with Cisco IOS XR QoS configuration tasks and concepts.
Packet Classification Overview, page 8
Traffic Class Elements, page 9
Traffic Policy Elements, page 9
Default Traffic Class, page 10
Class-based Unconditional Packet Marking Feature and Benefits, page 10
Specification of the CoS for a Packet with IP Precedence, page 11
IP Precedence Compared to IP DSCP Marking, page 12
Hierarchical Ingress Policing, page 13
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