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flow-control-queue (Output Congestion Notification)

 

Syntax

Hierarchy Level

Release Information

Statement introduced in Junos OS Release 12.3 for the QFX Series.

Description

Specify one or more output queues to pause, to support priority-based flow control (PFC). The specified queues pause when the interface receives a PFC frame with a matching IEEE 802.1p code point.

Default

Queue 3 (mapped to the fcoe forwarding class) and queue 4 (mapped to the no-loss forwarding class) are programmed as flow control queues to pause. No other output queues are programmed to pause by default.

If you configure flow control queues explicitly, only the queues that you specify are programmed to pause. The explicit flow control queue to pause configuration overrides the default setting, so the queues paused in the default configuration are no longer paused by default.

For example, if you configure queue 2 as a flow control queue, then queue 2 pauses when congestion occurs, but queues 3 and 4 do not pause because they were not explicitly specified. To enable pause on output queues 2, 3, and 4, you must explicitly configure all three of the queues as flow control queues.

The same behavior applies to the IEEE 802.1p code points (priorities) on which PFC is enabled. By default, priorities 3 (011) and 4 (100) are enabled for PFC pause. If you explicitly configure flow control queues to pause, you must also explicitly configure pause for each priority (code point) that you want to pause, because the explicit configuration overrides the default configuration.

Options

[ queue | list-of-queues]—The output queue or a list of output queues to pause.

Required Privilege Level

interfaces—To view this statement in the configuration.

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