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Example: Configuring Queue Scheduling Priority

Requirements

• A Juniper Networks QFX3500 Switch
• Junos OS Release 11.1 or later for the QFX Series

Overview

Queues can have one of two bandwidth priorities:

• strict-high—You can configure only one queue as a strict-high or high-priority queue. Strict-high priority allocates the scheduled bandwidth to the queue before any other queue receives bandwidth. Other queues receive the bandwidth that remains after the strict-high queue has been serviced.

  Note: If you configure strict-high priority queues, you must create an fc-set that is dedicated only to strict-high priority traffic. Only one fc-set can contain strict-high priority queues. Queues that are not strict-high priority cannot belong to the same fc-set as strict-high priority queues. The multidestination fc-set cannot contain strict-high priority queues.

  We recommend that you always apply a shaping rate to strict-high priority queues to prevent them from starving other queues. If you do not apply a shaping rate to limit the amount of bandwidth a strict-high priority queue can use, then the strict-high priority queue can use all of the available port bandwidth and starve other queues on the port.

• low—Low priority. Traffic with this priority is serviced after any queue that has a strict-high priority.

Table 1 shows the configuration components for this example.

This example describes how to set the queue priority for two forwarding classes (queues) named fcoe and no-loss. Both queues have a priority of low. The scheduler for the fcoe queue is named fcoe-sched and the scheduler for the no-loss queue is named nl-sched. One scheduler map, schedmap1, associates the schedulers to the queues.

Configuring Queue Scheduling Priority

1. Create the FCoE scheduler with low priority:
   [edit class-of-service]
user@switch# set schedulers fcoe-sched priority low
2. Create the no-loss scheduler with low priority:
   [edit class-of-service]
user@switch# set schedulers nl-sched priority low
3. Associate the schedulers with the desired queues in the scheduler map:
   [edit class-of-service]
user@switch# set scheduler-maps schedmap1 forwarding-class fcoe scheduler fcoe-sched
user@switch# set scheduler-maps schedmap1 forwarding-class no-loss scheduler nl-sched

Verification

To verify that you configured the queue scheduling priority for bandwidth and mapped the schedulers to the correct forwarding classes, perform these tasks:

• Verifying the Queue Scheduling Priority
• Verifying the Scheduler-to-Forwarding-Class Mapping

Verifying the Queue Scheduling Priority

Purpose

Verify that you configured the queue schedulers fcoe-sched and nl-sched with low queue scheduling priority.

Action

Display the fcoe-sched scheduler priority configuration using the operational mode command show configuration class-of-service schedulers fcoe-sched priority:

priority low;

Display the nl-sched scheduler priority configuration using the operational mode command show configuration class-of-service schedulers nl-sched priority:

priority low;

Verifying the Scheduler-to-Forwarding-Class Mapping

Purpose

Verify that you configured the scheduler map schedmap1 to map scheduler fcoe-sched to forwarding class fcoe and schedule nl-sched to forwarding class no-loss.

Action

Display the scheduler map schedmap1 using the operational mode command show configuration class-of-service scheduler-maps schedmap1:

forwarding-class fcoe scheduler fcoe-sched;
forwarding-class no-loss scheduler nl-sched;