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Cisco IOS Cookbook, 2nd Edition by Ian Brown, Kevin Dooley

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QoS over MPLS

Problem

You want to use the Quality of Service (QoS) features of MPLS.

Solution

For this example, we will take a relatively simple view that the PE router will trust the CE router’s DSCP/IP Precedence settings and map them to the MPLS EXP traffic priority field in a simple way. So we will focus on the configuration required on the PE and P routers to make use of this information.

First, the PE routers have the dual function of converting DSCP or IP Precedence values to MPLS EXP values and then using this information appropriately when forwarding the packets into the MPLS cloud. In this example, we will do both of these functions in a single policy map.

This MPLS network supports four categories of user traffic: low, medium, and high priority plus a real-time queue, which is indicated with the Expedited Forwarding (EF) DSCP value:

Router-PE1#configure terminal
Router-PE1(config)#class-map match-any med-priority
Router-PE1(config-cmap)#match precedence 1
Router-PE1(config-cmap)#match precedence 2
Router-PE1(config-cmap)#exit
Router-PE1(config)#class-map match-any high-priority
Router-PE1(config-cmap)#match precedence 3
Router-PE1(config-cmap)#match precedence 4
Router-PE1(config-cmap)#match precedence 5
Router-PE1(config-cmap)#exit
Router-PE1(config)#class-map match-any realtime-priority
Router-PE1(config-cmap)#match precedence 6
Router-PE1(config-cmap)#match dscp ef
Router-PE1(config-cmap)#exit
Router-PE1(config)#policy-map MPLS-priority
Router-PE1(config-pmap)#class realtime-priority ...

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