About Priority Flow Control
Priority-based flow control (PFC) pause frames are used in lossless ethernet to pause the link partner from sending packets. These PFC pause frames can propagate throughout the entire network and can cause the traffic on the PFC streams to halt.
About Priority Flow Control Watchdog
The PFC watchdog is a mechanism designed to detect and resolve any PFC storms (queue-stuck condition) in the network. You can configure a PFC watchdog interval to detect whether packets in a no-drop queue are drained within a specified time period. When this time period is exceeded, all outgoing packets are dropped on interfaces that match the PFC queue that is not being drained.
![]() Note |
The PFC watchdog feature is supported only for no-drop queue. |
Workflow of Priority Flow Control Watchdog
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Monitors the PFC-enabled queues to identify the reception of an excessive number of PFC pause frames in a given interval (Watchdog interval).
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Monitors when an excessive number of PFC frames are received and traffic on the corresponding queues is halted for a specified time interval (auto + fixed multiplier).
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Initiates the shutdown timer and changes the queue's state to wait-to-shutdown.
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Drops all data packets when the queue transitions to a shut state if interface multiplier time exceeds (if the interface multiplier is configured) or shutdown multiplier timer expire exceeds (if the interface multiplier is not configured).
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Checks the queue for PFC frames and whether the traffic in the queue is still stuck at regular intervals (poll timer of 100ms) during the shutdown interval.
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If traffic is stuck in the queue as PFC packets continue to arrive, the queue stays in the drop or shutdown state.
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If the traffic is not stuck because the queue didn't receive any PFC frames, the queue reverts to the monitored state.
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Checks if the queue is stuck because of PFC frames when the traffic is no longer stuck at regular intervals, the auto-restore timer starts.
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If the queue receives PFC frames during the last auto-restore interval (poll timer * auto-restore multiplier), the auto-restore timer (secs) is reset at its expiration.
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If the queue receives no PFC frames during the last auto-restore interval, the watchdog module restores the queue, and traffic resumes.
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