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Priority Flow Control (PFC) is a mechanism used in data center networks to ensure lossless transmission for high-priority traffic by pausing traffic when congestion is detected. While PFC helps in managing traffic congestion, it can potentially lead to a situation known as a PFC deadlock. To address this issue, network devices employ a PFC watchdog mechanism to detect and mitigate PFC deadlocks.
Understanding PFC Deadlock
A PFC deadlock occurs when multiple devices in a network are continuously sending PFC pause frames to each other, leading to a situation where traffic is indefinitely paused, causing a complete halt in data transmission. This deadlock can severely impact network performance and application availability.
PFC Watchdog Mechanism
The PFC watchdog is designed to detect and resolve PFC deadlocks. It monitors the duration of PFC pause frames and takes corrective actions if a potential deadlock is detected.
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Deadlock Detection: When the duration of a PFC pause frame surpasses the timeout threshold, the PFC watchdog triggers a deadlock detection process. This process identifies the ports and priority classes involved in the deadlock.
Restore Actions: Once a potential deadlock is detected, the PFC watchdog takes restore actions to break the deadlock. These actions typically include:
Forward: During the PFC deadlock recovery process, the received PFC PAUSE frame will be ignored, and the internal scheduler will resume forwarding the traffic.
Drop: drops Drops received data packets.
The restore actioncan be configured by the following commands:
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set class-of-service pfc-watchdog code-point <cos> restore-interval <restore-interval>
Restrictions and Guidelines
When you configure PFC watchdog, follow these restrictions and guidelines:
PFC should be enabledon the interface before enabling PFC watchdog.
PFC watchdog is only supported on Trident3-X5, Trident3-X7 and Tomahawk3 platforms.
Configuring PFC Watchdog
Procedure
Step 1 Enable PFC on the interface before enabling PFC watchdog.
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Step 5 Commit the configuration.
commit
Verifying the Configuration
After the configuration, use command run show pfc-watchdog config to view the configuration information about PFC watchdog.
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