Modular QoS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

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Modular QoS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

QoS marking for IP-to-MPLS traffic

Updated: June 9, 2026

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Details QoS marking for IP-to-MPLS traffic, including DSCP-to-EXP mapping, ingress remarking, platform support, limitations, benefits, and configuration requirements for consistent service differentiation.

QoS marking for IP-to-MPLS traffic is a QoS traffic differentiation feature that

transfers the DSCP value into the MPLS experimental (EXP) field when IP packets are encapsulated into MPLS
maintains end-to-end service differentiation across the IP and MPLS domains by aligning per-hop behaviors between IP and label-switched segments, and
enables consistent QoS treatment for customer traffic traversing MPLS networks through DSCP-to-EXP mapping configured in QoS policies.

This feature ensures that traffic classified at the IP layer retains its intended QoS behavior as it transits an MPLS-enabled core, preserving prioritization and congestion-handling characteristics across heterogeneous domains.

Table 1. Feature History Table
Feature Name	Release Information	Feature Description
Mark IP DSCP and MPLS EXP Values for IP to MPLS Traffic	Release 7.5.4	We’ve provided you with more granular control for IP to MPLS traffic, so you can collect billing information for your customers upstream at the MPLS core and correlate them with subsequent next-hop IP nodes. This helps you accurately bill your customers as they pay for specific services based on their network requirements. Such control is possible because we’ve enabled the remarking of IP DSCP values in the inner IP header—that remain even after the POP tag removes the outer header—along with the existing ability to remark MPLS EXP values on the outer MPLS header. There’s no action required for you to enable this functionality, and there are no changes to command options.

QoS behavior for DSCP and EXP marking in IP-to-MPLS encapsulation

In earlier software releases, remarking the DSCP value in an ingress QoS policy for IP-to-MPLS traffic resulted in incomplete propagation of the marked value.

The inner IP header retained its original DSCP value, preventing the intended QoS action from being applied across the network.
The outer MPLS header, however, received the remarked value through the EXP bits that reflected the QoS policy action.

Starting from Cisco IOS XR Release 7.5.4, the QoS marking behavior for IP packets transiting an MPLS core has been enhanced.

During MPLS imposition, the inner IP header now receives the remarked DSCP value from the ingress QoS policy, ensuring that the IP packet carries consistent QoS intent across the network.
The top MPLS label continues to receive the remarked EXP value, derived from the three most significant bits of the DSCP field.

Benefits of QoS marking for IP-to-MPLS traffic

The ability to remark IP DSCP and MPLS EXP values at the ingress provides:

Granular QoS control across multiple hops, ensuring consistent per-hop behavior and prioritization across both IP and MPLS domains.
Improved service visibility, enabling correlation between traffic treatment in the IP edge and forwarding performance in the MPLS core.
Enhanced operational efficiency, allowing service providers to collect and align customer-specific billing or usage data with the QoS policies applied at different network layers.

Limitations for configuring QoS marking for IP-to-MPLS traffic

This feature is supported only on Cisco Silicon One Q200–based ASICs, available in both fixed and distributed systems.
In distributed systems, you can use a Cisco Silicon One Q100–based ASIC line card for ingress classification; however, the egress line card must be equipped with a Q200 ASIC.

Configure QoS marking for IP-to-MPLS encapsulated traffic

Before you begin

Complete these prerequisites before you begin:

Ensure MPLS forwarding and label imposition are enabled on the PE router interfaces.
Verify that class maps and policy maps required for ingress DSCP remarking and egress classification are defined in your configuration plan.
Confirm that the platform uses Cisco Silicon One Q200–based ASICs for egress functionality.

Procedure

Create an ingress class map and policy map to remark DSCP values for IP packets before MPLS encapsulation.

This configuration sets the DSCP value to AF41 for traffic originally marked as AF31 to define a higher assured forwarding PHB.

Example:


Router(config)#class-map AF31
Router(config-cmap)#match dscp AF31
Router(config-cmap)#end-class-map
Router(config)#
Router(config)#policy-map INGRESS_REMARK
Router(config-pmap)#class AF31
Router(config-pmap-c)#set dscp AF41
Router(config-pmap-c)#end-policy-map
Router(config)#
Router(config)#interface FourHundredGigE0/0/0/0
Router(config-if)#service-policy input INGRESS_REMARK
Router(config-if)#commit

Create an egress class map and policy map to classify packets based on remarked DSCP values.

This configuration classifies incoming traffic as AF31 or AF41 and maps it to the appropriate traffic-class values for forwarding decisions.

Example:


Router(config)#class-map AF31
Router(config-cmap)#match dscp AF31
Router(config-cmap)#end-class-map
Router(config)#
Router(config)#class-map AF41
Router(config-cmap)#match dscp AF41
Router#end-class-map
Router(config)#
Router(config)#policy-map INGRESS_CLASSIFY
Router(config-pmap)#class AF31
Router(config-pmap-c)#set traffic-class 3
Router(config-pmap-c)#exit
Router(config-pmap)# 
Router(config-pmap)#class AF41
Router(config-pmap-c)#set traffic-class 4
Router(config-pmap-c)#exit
Router(config-pmap)#end-policy-map
Router(config)#
Router(config)#int FourHundredGigE0/0/0/1
Router(config-if)#service-policy input INGRESS_CLASSIFY
Router(config-if)#commit

Verify DSCP remarking and classification at the egress PE router.

Use the show policy-map interface command to verify that traffic marked as AF41 at ingress is now being classified and counted correctly at egress.

Example:

Router#show policy-map interface FourHundredGigE0/0/0/1 input
 
FourHundredGigE0/0/0/1 input: INGRESS_CLASSIFY
 
Class AF31
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0
Class AF41
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :             9813350/13738690000          936847
    Transmitted         :             9813350/13738690000          936847
    Total Dropped       :                   0/0                    0
Class class-default
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0

The nonzero counters for Class AF41 confirm that the ingress DSCP remarking has been applied successfully and is recognized at the egress PE router.

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