Tài liệu Classification and Marking docx

Classification and

Marking

Overview

This module describes the mechanisms that are used to classify and mark IP

packets. This module builds on the knowledge acquired from the introductory

module where classification and marking is discussed. Theoretical knowledge is

supplemented by detailing Policy-based routing (PBR) and QoS Policy Propagation

through BGP (QPPB) mechanisms.

Objectives

Upon completion of this module, you will be able to:

n Describe Policy-based routing and how it is used to classify and mark IP

packets

n Describe QoS Policy Propagation through BGP and how it is used to classify

and mark IP packets

n List other mechanisms that also support classification and marking capabilities

(Committed Access Rate, Class-based Policing and Class-based Marking)

2-2 IP QoS Classification and Marking Copyright ” 2001, Cisco Systems, Inc.

© 2001, Cisco Systems, Inc. Classification and Marking-3

Traffic Classification and Marking

Classification

• Most QoS mechanisms in the Cisco IOS

include some type of classification

• Some mechanisms classify packets

automatically, some require manual

configuration

Marking

• Only a small number of mechanisms also

include a marking capability

This module focuses on the QoS mechanisms that are used for classification and

marking purposes only. Most QoS mechanisms include some type of classification

but only a small number of mechanisms also include marking capability.

Classification is the term used for identifying a Behavior Aggregate to which a

packet belongs. A Behavior Aggregate is a collection of flows requiring the same

quality of service.

Marking is the term used for coloring packets by applying a class-identifying

value to one of the following markers: IP precedence, DSCP, QoS group (value is

local to a router), MPLS experimental bits (can be used only in MPLS-enabled

networks), ATM CLP bit (value can be used only within ATM networks), Frame

Relay DE bit (value can be used only within Frame Relay networks), IEEE 802.1q

or ISL cos/priority bits (value can be used on within LAN-switched networks).

Copyright ” 2001, Cisco Systems, Inc. IP QoS Classification and Marking 2-3

© 2001, Cisco Systems, Inc. Classification and Marking-4

Traffic Classification and Marking

• This module describes the two mechanisms

that are used for classification and marking

only:

– Policy-based Routing (PBR)

– QoS Policy Propagation through BGP (QPPB)

• Other classification and/or marking

mechanisms are described in other QoS

modules

This module describes the two QoS mechanisms that are used purely for

classification and marking purposes:

n Policy-based Routing (PBR)

n QoS Policy Propagation through BGP (QPPB)

There are other QoS mechanisms that also support classification and marking:

n Committed Access Rate (CAR) – this mechanism is described in the “IP

QoS – Traffic Shaping and Policing” module

n Class-based Policing (CB-Policing) – this mechanism is described in the

“IP QoS – Modular QoS CLI (Chapter 2)” module

n Class-based Marking (CB-Marking) – this mechanism is described in the

“IP QoS – Modular QoS CLI (Chapter 2)” module

2-4 IP QoS Classification and Marking Copyright ” 2001, Cisco Systems, Inc.

Policy-based Routing

Objectives

Upon completion of this lesson, you will be able to:

n Describe Policy Based Routing (PBR)

n Configure PBR on Cisco routers

n Monitor and troubleshoot PBR

Copyright ” 2001, Cisco Systems, Inc. IP QoS Classification and Marking 2-5

© 2001, Cisco Systems, Inc. Classification and Marking-7

Policy-based Routing

• Policy-based Routing (PBR) is a mechanism

that can be used to bypass the default

destination-based forwarding functionality of

routers

• PBR is implemented using a route map

where match commands are used to classify

packets and set commands are used to

process packets

• Route maps are applied to interfaces for

processing of inbound packets (forwarding

and/or marking)

The primary function of Policy-based Routing (PBR) is to bypass the

destination-based forwarding functionality of routers by using a route map to make

a forwarding decision based on other information.

One additional feature of Policy Based Routing is the ability to modify IP packets

by marking them with IP precedence or QoS group.