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

PDF

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

Traffic shaping

Updated: June 9, 2026

Want to summarize with AI?

Log in

Explains traffic shaping for regulating outbound traffic rates, including main interface shaping, subinterface class-level shaping, configuration guidelines, and verification of policy behavior.

Traffic shaping is a QoS congestion management feature that

  • regulates the flow of outbound traffic to match the speed or bandwidth profile of the downstream interface

  • buffers excess packets during congestion instead of dropping them, and

  • ensures traffic conforms to contracted or expected rate profiles to prevent bottlenecks in topologies with data-rate mismatches.

Key functions of traffic shaping

  • Buffering: is a key function of traffic shaping in which excess packets are temporarily stored instead of being dropped, allowing the system to release them later at a controlled rate when bandwidth becomes available.

  • Rate profiling: is a traffic-control concept that defines the maximum transmission rate a flow must conform to so that it matches the expected bandwidth or contract of the downstream interface.

Guidelines for configuring traffic shaping

Supported traffic direction

Only egress traffic shaping is supported.

Class and policy requirements

  • You must configure all eight qos-group classes—including class-default—in the egress QoS policy.

  • You can configure the shape average command together with the priority command when shaping traffic.

  • We recommended that you configure all eight traffic-class classes—including class-default—in the egress policies.

  • Only a limited set of traffic-class class combinations is supported.

Traffic-type considerations

Egress interfaces that carry both unicast and multicast traffic may handle traffic classes inconsistently when shaping is enabled. Therefore, configure shaping primarily on ports that carry only unicast traffic.

Configure traffic shaping

This procedure applies only to configuring traffic shaping on main interfaces.

Before you begin

Ensure that you have an existing QoS class map for the traffic class you intend to shape.

Follow these steps to configure traffic shaping on a main interface.

Procedure

1.

Create or modify a policy-map to configure traffic shaping for a specific class.

This policy-map defines the shaping rate applied to the outbound traffic class.

Example:

Router# configure
Router(config)# policy-map egress_policy1
Router(config-pmap)# class c5
Router(config-pmap-c)# shape average percent 40
Router(config-pmap-c)# exit
Router(config-pmap)# exit

The policy-map now includes a shaping configuration for the selected traffic class.
2.

Attach the shaping policy-map to the egress interface.

Applying the service policy activates traffic shaping for outbound traffic on that interface.

Example:

Router(config)# interface HundredGigE 0/1/0/0
Router(config-if)# service-policy output egress_policy1
Router(config-if)# commit

The traffic shaping configuration is now active on the selected output interface.

Running Configuration

policy-map egress_policy1
 class c5
  shape average percent 40
 !
 class class-default
 !
 end-policy-map
!

interface HundredGigE0/6/0/18
 service-policy input 100g-s1-1
 service-policy output egress_policy1
!
3.

Verify the shaping configuration on the interface.

Check that the class displays the expected shaping rate and queue behavior.

Example:

Router# show qos interface HundredGigE 0/6/0/18 output
            
 NOTE:- Configured values are displayed within parentheses
Interface HundredGigE0/6/0/18 ifh 0x3000220  -- output policy
NPU Id:                        3
Total number of classes:       2
Interface Bandwidth:           100000000 kbps
VOQ Base:                      11176
VOQ Stats Handle:              0x88550ea0
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   c5
Egressq Queue ID                         =   11177 (LP queue)
Queue Max. BW.                           =   40329846 kbps (40 %)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 (BWR not configured)
Guaranteed service rate                  =   40000000 kbps
TailDrop Threshold                       =   50069504 bytes / 10 ms (default)
WRED not configured for this class

Level1 Class                             =   class-default
Egressq Queue ID                         =   11176 (Default LP queue)
Queue Max. BW.                           =   101803495 kbps (default)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 (BWR not configured)
Guaranteed service rate                  =   50000000 kbps
TailDrop Threshold                       =   62652416 bytes / 10 ms (default)
WRED not configured for this class

The interface output shows that shaping is applied with the configured rate and class behavior.

Egress class-level traffic shaping on subinterfaces

Egress class-level traffic shaping on subinterfaces is a QoS traffic shaping feature that

  • provides class-level rate limiters or shaping on each traffic class in an egress subinterface queuing policy map

  • provides granular control of outbound traffic on individual classes, and

  • enables efficient bandwidth allocation when multiple services share the same physical link or LAG.

Table 1. Feature History Table

Feature Name

Release Information

Feature Description

Egress class-level traffic shaping for subinterfaces

 Release 26.1.1

Introduced in this release on: Centralized Systems (8400 [ASIC: K100])(select variants only*)

* This feature is now supported on Cisco 8404-SYS-D routers.

Egress class-level traffic shaping for subinterfaces

Release 25.4.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100], 8700 [ASIC: K100])

*This feature is supported on:

  • 8011-32Y8L2H2FH

  • 8011-12G12X4Y-A/D

  • 8711-48Z-M

Egress class-level traffic shaping for subinterfaces

 Release 25.1.1

Introduced in this release on: Fixed Systems (8700 [ASIC: K100], 8010 [ASIC: A100])(select variants only*)

Egress class-level traffic shaping for subinterfaces is now supported on the fixed systems using K100 and A100 Silicon One ASICs.

This feature is supported on:

  • 8712-MOD-M

  • 8011-4G24Y4H-I

Egress class-level traffic shaping for subinterfaces

Release 24.3.1

Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100])(select variants only*); Modular Systems (8800 [LC ASIC: P100])(select variants only*)

You can now granularly control the traffic flow on each class in the egress queuing policy map ensuring optimal bandwidth allocation and improved network performance.

This is achieved by introducing support for enabling class-level rate limiting traffic shapers for each class in the egress subinterface-level (main and LAG) queuing policy maps.

*This feature is enabled by default and supported on:

  • 8212-48FH-M

  • 8711-32FH-M

  • 88-LC1-36EH

  • 88-LC1-12TH24FH-E

  • 88-LC1-52Y8H-EM

Guidelines for configuring egress class-level traffic shaping on subinterfaces

Traffic-type considerations

Shaping of multicast traffic is not supported on egress subinterfaces configured in the non-ETM mode.