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Defining CoS Queue Scheduling Priority

You can configure the scheduling priority of individual queues by specifying the priority in a scheduler, and then associating the scheduler with a queue by using a scheduler map.

Note:

By default, all queues are low priority queues.

The switch services low priority queues after servicing any queue that has strict-high priority traffic or high priority traffic. Strict-high priority queues receive preferential treatment over all other queues and receive all of their configured bandwidth before other queues are serviced. Low-priority queues do not transmit traffic until strict-high priority queues are empty, and receive the bandwidth that remains after the strict-high queues have been serviced. High priority queues receive preference over low priority queues.

  • To configure queue priority using the CLI:

Platform-Specific Behavior

Use the following table to review platform-specific behaviors for your platforms.

Table 1: Platform-Specific Behavior

Platform

Difference

QFX5000 Series and EX4600

  • On QFX5100 and EX4600 switches, you can configure only one forwarding-class-set (priority group) as strict-high priority. All queues which are part of that strict-high forwarding class set then act as strict-high queues.

  • On QFX5200 switches, it is not possible to support multiple queues with strict-high priority because QFX5200 doesn’t support flexible hierarchical scheduling. When multiple strict-high priority queues are configured, all of those queues are treated as strict-high priority but the higher number queue among them is given highest priority.

  • On QFX5200, QFX5100, and EX4600 switches, apply a shaping rate to strict-high priority queues to prevent those queues from starving other queues on the port.

QFX10000 Series

  • On QFX10000 switches, you can configure as many queues as you want as strict-high priority queues.

  • On QFX10000 switches, apply a transmit rate to strict-high priority queues to prevent those queues from starving other queues on the port.

  • QFX10000 switches treat traffic in excess of the transmit rate as best-effort traffic that receives bandwidth from the leftover (excess) port bandwidth pool.

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