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priority (Schedulers)


Hierarchy Level


Specify the packet bandwidth-scheduling priority value.


On QFabric systems, the priority statement is valid only for Node device queue scheduling. The priority statement is notallowed for Interconnect device queue scheduling. If you map a schedulerthat includes a priority configuration to a fabric forwardingclass at the [edit class-of-service scheduler-map-fcset] hierarchylevel, the system generates a commit error. (On the Interconnect device,fabric fc-sets are not user-definable. Only the fabric_fcset_strict_high fabric fc-set is configured with high priority, and this configurationcannot be changed.)


priority—It can be one of the following:

  • low—Scheduler has low priority.

  • medium-low—Scheduler has medium-low priority. (QFX10000 Series switches only)

  • medium-high—Scheduler has medium-high priority. (QFX10000 Series switches only)

  • high—Scheduler has high priority. Assigning high priority to a queue prevents the queue from being underserved. (QFX10000 Series switches only)

  • strict-high—Scheduler has strict high priority. On QFX5100, EX4600, QFX3500, and QFX3600 switches, and on QFabric systems, you can configure only one queue as a strict-high priority queue. On QFX10000 switches, you can configure as many strict-high priority queues as you want. However, because strict-high priority traffic takes precedence over all other traffic, too much strict-high priority traffic can starve the other output queues.

    Strict-high priority allocates the scheduled bandwidth to the packets on the queue before any other queue receives bandwidth. Other queues receive the bandwidth that remains after the strict-high queue has been serviced.


    On QFX10000 switches, we strongly recommend that you apply a transmit rate to strict-high priority queues to prevent them from starving other queues. A transmit rate configured on a strict-high priority queue limits the amount of traffic that receives strict-high priority treatment to the amount or percentage set by the transmit rate. The switch treats traffic in excess of the transmit rate as best-effort traffic that receives bandwidth from the leftover (excess) port bandwidth pool. On strict-high priority queues, all traffic that exceeds the transmit rate shares in the port excess bandwidth pool based on the strict-high priority excess bandwidth sharing weight of “1”, which is not configurable. The actual amount of extra bandwidth that traffic exceeding the transmit rate receives depends on how many other queues consume excess bandwidth and the excess rates of those queues.

    On QFX5100, EX4600, QFX3500, and QFX3600 switches, and on QFabric systems, we recommend that you always apply a shaping rate to strict-high priority queues to prevent them from starving other queues. A shaping rate (shaper) sets the maximum amount of bandwidth a queue can consume. (Unlike using the transmit rate on a QFX10000 switch to limit traffic that receives strict-high priority treatment, traffic that exceeds the shaping rate is dropped, and is not treated as best-effort traffic that shares in excess bandwidth.) 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.

Required Privilege Level

interface—To view this statement in the configuration.

interface-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 11.1.

medium-low and medium-low options introduced for QFX10000 Series switches in Junos OS 19.2R3.