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Configuring Strict High Priority for Queuing

On a Services Router, you can configure one queue per interface to have strict high priority, which causes delay-sensitive traffic, such as voice traffic, to be dequeued and forwarded with minimum delay. Packets that are queued in a strict-priority queue are dequeued before packets in other queues, including high-priority queues.

The strict high-priority queuing feature allows you to configure traffic policing that prevents lower-priority queues from being starved. The strict-priority queue does not cause starvation of other queues because the configured policer allows the queue to exceed the configured bandwidth only when other queues are not congested. If the interface is congested, the software polices strict-priority queues to the configured bandwidth.

To prevent queue starvation of other queues, you must configure an output (egress) policer that defines a limit for the amount of traffic that the queue can service. The software services all traffic in the strict-priority queue that is under the defined limit. When strict-priority traffic exceeds the limit, the policer marks the traffic in excess of the limit as out-of-profile. If the output port is congested, the software drops out-of-profile traffic.

The out-of-profile limit does not work when you configure shaping on the interface.

You can also configure a second policer with an upper limit. When strict-priority traffic exceeds the upper limit, the software drops the traffic in excess of the upper limit, regardless of whether the output port is congested. This upper-limit policer is not a requirement for preventing starvation of the lower-priority queues. The policer for the lower limit, which marks the packets as out-of-profile, is sufficient to prevent starvation of other queues.

The sample strict-high priority queuing configuration does the following:

  1. Uses a behavior aggregate (BA) classifier to classify traffic based on the IP precedence of the packet. The classifier defines IP precedence value 101 as voice traffic and 000 as data traffic.
  2. To minimize delay, assigns all delay-sensitive packets to the strict-priority queue.
  3. Configures two policers on the output interface that identify excess voice traffic belonging to the voice-class forwarding class. If the traffic exceeds 1 Mbps, a policer marks the traffic in excess of 1 Mbps as out-of-profile. If the traffic exceeds 2 Mbps, the second policer discards the traffic in excess of 2 Mbps.

To configure strict-priority queuing and prevent starvation of other queues:

  1. Navigate to the top of the configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 138.
  3. If you are finished configuring the router, commit the configuration.

Table 138: Configuring Strict-High Priority Queuing and Starvation Prevention

Task

J-Web Configuration Editor

CLI Configuration Editor
Configuring a BA Classifier

Use a BA classifier to classify traffic based on the IP precedence of the packet. The classifier defines IP precedence value 101 as voice traffic and 000 as data traffic.

  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Class of service, click Configure or Edit.
  3. Next to Classifiers, click Configure or Edit.
  4. Next to Inet precedence, click Add new entry.
  5. Enter corp-traffic in the Name box.
  6. Next to Forwarding class, click Add new entry.
  7. Enter voice-class in the Class name box.
  8. Next to Loss priority, click Add new entry.
  9. Enter low in the Loss val box.
  10. Next to Code points, click Add new entry.
  11. Enter 101 in the Value box.
  12. Click OK three times.
  13. In the Inet precedence forwarding class page, enter voice-class in the Class name box.
  14. Next to Loss priority, click Add new entry.
  15. Enter high in the Loss val box.
  16. Next to Code points, click Add new entry.
  17. Enter 000 in the Value box.
  18. Click OK five times.

From the [edit] hierarchy level, enter

edit Class of service classifiers inet-precedence corp-traffic forwarding-class voice-class loss-priority low

Enter set code-points 101

From the [edit] hierarchy level, enter

edit class-of-service classifiers inet-precedence corp-traffic forwarding-class data-class loss-priority high

Enter set code-points 000

Configuring the Forwarding Classes

Assign priority queuing to voice and data traffic.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Class of service, click Configure or Edit.
  3. Next to Forwarding classes, click Configure or Edit.
  4. Next to Queue, click Add new entry.
  5. Enter 0 in the Queue num box.
  6. Enter voice-class in the Class name box.
  7. Click OK to return to the Forwarding Classes page.
  8. Next to Queue, click Add new entry.
  9. Enter 1 in the Queue num box.
  10. Enter data-class in the Class name box.
  11. Click OK three times.

From the [edit] hierarchy level, enter

edit class-of-service forwarding-classes queue 0 voice-class

enter

edit class-of-service forwarding-classes queue 1 data-class

Configuring the Scheduler Map and Schedulers

Configure the scheduler map and voice scheduler.

  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Class of service, click Configure or Edit.
  3. Next to Scheduler maps, click Add new entry.
  4. In the Map name box, type corp-map.
  5. Next to Forwarding class, click Add new entry.
  6. In the Class name box, type voice-class.
  7. In the Scheduler name box, type voice-sched.
  8. Click OK three times.

From the [edit] hierarchy level, enter

edit class-of-service scheduler-maps corp-map forwarding-class voice-class

Enter

set scheduler voice-sched

Define the voice and data traffic schedulers, and set the priority.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Class of service, click Configure or Edit.
  3. Next to Schedulers, click Add new entry.
  4. In the Scheduler name box, type voice-sched.
  5. In the Priority box, type strict-high.
  6. Click OK.
  7. Next to Schedulers, click Add new entry.
  8. In the Scheduler name box, type data-sched.
  9. In the Priority box, type low.
  10. Click OK twice.

From the [edit] hierarchy level, enter

edit class-of-service schedulers voice-sched

Enter

set priority strict-high

From the [edit] hierarchy level, enter

edit class-of-service schedulers data-sched

Enter

set priority low

Applying the BA Classifier to an Input Interface and Scheduler Map to an Output Interface

Apply the BA classifier to an input interface—for example, fe-0/0/0.

Apply the scheduler map to and output interface—for example, e1-1/0/0.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Interfaces, click Configure or Edit.
  3. Next to Interface, click Add new entry.
  4. In the Interface name box, type fe-0/0/0.
  5. Click OK three times.
  6. In the Edit Configuration page, next to Class of service, click Configure or Edit.
  7. Next to Classifiers, click Edit.
  8. Next to Inet precedence, click Add new entry.
  9. In the Name box, type corp-traffic.
  10. Click OK three times.
  11. In the Edit Configuration page, next to Interfaces, click Configure or Edit.
  12. Next to Interface name, type e1-1/0/1.
  13. Click OK twice.
  14. In the Edit Configuration page, next to Class of service, click Configure or Edit.
  15. Next to Scheduler maps, click Add new entry.
  16. In the Map name box, type corp-map.
  17. Click OK twice.

From the [edit] hierarchy level, enter

edit interfaces fe-0/0/0 unit 0

From the [edit] hierarchy level, enter

edit class of service classifiers inet-precedence corp-traffic

From the [edit] hierarchy level, enter

edit interfaces e1-1/0/0 unit 0

From the [edit] hierarchy level, enter

edit class-of-service scheduler-maps corp-map

Configuring Two Policers

Configure two policers: one as voice-drop and second as voice-excess.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Firewall, click Configure or Edit.
  3. Next to Policer, click Add new entry.
  4. In the Policer name box, type voice-drop.
  5. Next to If Exceeding, select the check box and click Configure.
  6. In the Burst size limit box, type 200000.
  7. In the Bandwidth list, select Bandwidth limit.
  8. In the Bandwidth limit box, type 2000000.
  9. Click OK.
  10. On the Policer page, next to Then, click Configure.
  11. Next to Discard, select the check box.
  12. Click Ok twice.
  13. In the Firewall Configuration page next to Policer, click Add new entry.
  14. In the Policer name box, type voice-excess.
  15. Next to If Exceeding, select the check box and click Configure.
  16. In the Burst size limit box, type 200000.
  17. In the Bandwidth list, select Bandwidth limit.
  18. In the Bandwidth limit box, type 1000000.
  19. Click OK.
  20. On the Policer page, next to Then, click Configure.
  21. Next to Out of profile, select the check box.
  22. Click OK twice.

From the [edit] hierarchy level, enter

edit firewall policer voice-drop if-exceeding

Enter

set burst-size-limit 200000 bandwidth-limit 2000000

Enter

set then discard

From the [edit] hierarchy level, enter

edit firewall policer voice-excess if-exceeding

Enter

set burst-size-limit 200000 bandwidth-limit 1000000

Enter

set then out-of-profile

Create a firewall filter voice-term that includes the new policers
  1. In the Firewall Configuration page next to Filter, click Add new entry.
  2. In the Filter name box, type voice-term.
  3. Next to Term click Add new entry.
  4. In the Rule name box, type term 01.
  5. Next to Term, click Add new entry.
  6. Next to From, click Configure.
  7. Next to Forwarding class choice, select forwarding-class.
  8. Next to Forwarding class, click Add new entry.
  9. In the String box, type voice-class.
  10. Click OK twice.
  11. In the Term Filter page, next to Then, click Configure.
  12. Next to Policer choice, select policer.
  13. In the Policer box, type voice-drop.
  14. Next to Designation, select Next.
  15. In the Next box, select term.
  16. Click OK twice.
  17. In the Firewall Filter page, next to Term, click Add new entry.
  18. In the Rule name box, type term 02.
  19. Next to From, click Configure.
  20. Next to Forwarding class choice, select forwarding-class.
  21. Next to Forwarding class, click Add new entry.
  22. In the String box, type voice-class.
  23. Click OK twice.
  24. In the Term Filter page, next to Then, click Configure.
  25. Next to Policer choice, select policer.
  26. In the Policer box, type voice-excess.
  27. Next to Designation, select Accept.
  28. Click OK four times.

From the [edit] hierarchy level, enter

edit firewall filter voice-term term 01 from forwarding-class voice-class then policer voice-drop next term

Enter

edit firewall filter voice-term term 02 from forwarding-class voice-class then policer voice-excess accept

Applying the Filter to the Output Interface

Apply filter voice-term to e1-1/0/0 using the CLI.

  

From the [edit] hierarchy level, enter

edit interfaces e1-1/0/1 unit 0 family inet filter output voice-term

Enter

set family inet address 11.1.1.1/24

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