Cisco Systems QC-29 Configuring Low-Latency Queueing with Strict Priority Queueing, Restrictions

Configuring Modular Quality of Service Congestion Management on Cisco IOS XR Software

How to Configure QoS Congestion Management on Cisco IOS XR Software

	Command or Action	Purpose
Step 13
	service-policy {input output} policy-map	Attaches a policy map to an input or output interface to be
		used as the service policy for that interface.
	Example:	• The traffic policy evaluates all traffic leaving that
	RP/0/RP0/CPU0:router(config-if)# service-policy	interface.
	output policy1
Step 14
	end	Saves configuration changes.
	or	• When you issue the end command, the system prompts
	commit	you to commit changes:
		Uncommitted changes found, commit them before
	Example:	exiting(yes/no/cancel)?
	RP/0/RP0/CPU0:router(config-if)# end	[cancel]:
	or	– Entering yes saves configuration changes to the
	RP/0/RP0/CPU0:router(config-if)# commit
		running configuration file, exits the configuration
		session, and returns the router to EXEC mode.
		– Entering no exits the configuration session and
		returns the router to EXEC mode without
		committing the configuration changes.
		– Entering cancel leaves the router in the current
		configuration session without exiting or
		committing the configuration changes.
		• Use the commit command to save the configuration
		changes to the running configuration file and remain
		within the configuration session.
Step 15
	show policy-map interface type instance [input	(Optional) Displays policy configuration information for all
	output]	classes configured for all service policies on the specified
		interface.
	Example:
	RP/0/RP0/CPU0:router# show policy-map interface
	POS 0/2/0/0

Configuring Low-Latency Queueing with Strict Priority Queueing

The priority command configures low-latency queueing (LLQ), providing strict priority queueing (PQ). Strict PQ allows delay-sensitive data, such as voice, to be dequeued and sent before packets in other queues are dequeued. When a class is marked as high priority using the priority command, we recommend that you configure a policer to limit the priority traffic. This configuration ensures that the priority traffic does not starve all of the other traffic on the line card, which protects low priority traffic from starvation. Use the police command to explicitly configure the policer.

Restrictions

Within a policy map, you can give one or more classes priority status. When multiple classes within a single policy map are configured as priority classes, all traffic from these classes is queued to the same single priority queue.

The bandwidth, priority, and shape average commands should not be configured together in the same class.

Cisco IOS XR Modular Quality of Service Configuration Guide

QC-40