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SRX Series

QFX Series

EX Series (Except EX4300)


M320, MX Series, T Series, and PTX Series

Hierarchy Level


Command used to associate forwarding classes with class names and queues with queue numbers.

SRX Series Firewalls

All traffic traversing the SRX Series Firewall is passed to an SPC to have service processing applied. Junos OS provides a configuration option to enable packets with specific Differentiated Services (DiffServ) code points (DSCP) precedence bits to enter a high-priority queue, a medium-priority queue, or a low-priority queue on the SPC. The Services Processing Unit (SPU) draws packets from the highest priority queue first, then from the medium priority queue, and last from the low priority queue. The processing of the queue is weighted-based not strict-priority-based. This feature can reduce overall latency for real-time traffic, such as voice traffic.

Initially, the spu-priority queue options were "high" and "low". Then, these options (depending on the devices) were expanded to "high", "medium-high", "medium-low", and "low". The two middle options ("medium-high" and "medium-low") have now been deprecated (again, depending on the devices) and replaced with "medium". So, the available options for spu-priority queue are "high", "medium", and "low".

We recommend that the high-priority queue be selected for real-time and high-value traffic. The other options would be selected based on user judgement on the value or sensitivity of the traffic.

M320, MX Series, and T Series Routers and EX Series Switches

For M320, MX Series, and T Series routers, and EX Series switches only, you can configure fabric priority queuing by including the priority statement. For Enhanced IQ PICs, you can include the policing-priority option.


The priority and policing-priority options are not supported on PTX Series routers.

EX Series Switches

For the EX Series switches, this statement associates the forwarding class with a class name and queue number. It can define the fabric queuing priority as high, medium-high, medium-low, or low.

Map one or more forwarding classes to a single output queue. Also, when configuring DSCP-based priority-based flow control (PFC), map a forwarding class to a PFC priority value to use in pause frames when traffic on a DSCP value becomes congested (see Configuring DSCP-based PFC for Layer 3 Untagged Traffic for details).

Switches that use different forwarding classes for unicast and multidestination (multicast, broadcast, and destination lookup fail) traffic support 12 forwarding classes and 12 output queues (0 through 11). You map unicast forwarding classes to a unicast queue (0 through 7) and multidestination forwarding classes to a multidestination queue (8 through 11). The queue to which you map a forwarding class determines if the forwarding class is a unicast or multidestination forwarding class.

Switches that use the same forwarding classes for unicast and multidestination traffic support eight forwarding classes and eight output queues (0 through 7). You map forwarding classes to output queues. All traffic classified into one forwarding class (unicast and multidestination) uses the same output queue.

You cannot configure weighted random early detection (WRED) packet drop on forwarding classes configured with the no-loss packet drop attribute. Do not associate a drop profile with lossless forwarding classes.


If you map more than one forwarding class to a queue, all of the forwarding classes mapped to the same queue must have the same packet drop attribute (all of the forwarding classes must be lossy, or all of the forwarding classes mapped to a queue must be lossless).


On switches that do not use the Enhanced Layer 2 Software (ELS) CLI, if you are using Junos OS Release 12.2, use the default forwarding-class-to-queue mapping for the lossless fcoe and no-loss forwarding classes. If you explicitly configure the lossless forwarding classes, the traffic mapped to those forwarding classes is treated as lossy (best effort) traffic and does not receive lossless treatment.


On switches that do not use the ELS CLI, if you are using Junos OS Release 12.3 or later, the default configuration is the same as the default configuration for Junos OS Release 12.2, and the default behavior is the same (the fcoe and no-loss forwarding classes receive lossless treatment). However, if you explicitly configure lossless forwarding classes, you can configure up to six lossless forwarding classes by specifying the no-loss option. If you do not specify the no-loss option in an explicit forwarding class configuration, the forwarding class is lossy. For example, if you explicitly configure the fcoe forwarding class and you do not include the no-loss option, the fcoe forwarding class is lossy, not lossless.


class class-name

Define the forwarding class name.

queue-num queue-number

Output queue number to associate with forwarding class.

  • Range: 0 through 7.


Fabric priority value:


Forwarding class fabric queuing has high priority.


Forwarding class fabric queuing has low priority.

The default priority is low.


SPU priority queue, high, medium, or low. The default spu-priority is low.


The spu-priority option is supported only on the SRX5000 line of firewalls.

The remaining statements are explained separately. See CLI Explorer for details.

Required Privilege Level

interface—To view this statement in the configuration.

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

Release Information

The policing-priority option was introduced in Junos OS Release 9.5.

Statement updated in Junos OS Release 11.4.

The spu-priority option was introduced in Junos OS Release 11.4R2.

The no-loss option was introduced in Junos OS Release 12.3.

Change from two to four queues made in Junos OS Release 12.3X48-D40 and in Junos OS Release 15.1X49-D70.

The pfc-priority statement was introduced in Junos OS Release 17.4R1.

The medium-high and medium-low priorities for spu-priority were deprecated and medium priority was added in Junos OS Release 19.1R1.