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Home Documentation Junos OS Evolved AI-ML Data Center Feature Guide Traffic Management

AI-ML Data Center Feature Guide

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AI-ML Data Center Feature Guide
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PFC Watchdog

date_range 12-Nov-24
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Overview

In a lossless AI Ethernet fabric, priority-based flow control (PFC) allows independent flow control for each class of service to ensure that congestion does not result in frame loss. PFC pause frames instruct the link partner to halt packet transmission. These frames can propagate through the network, causing traffic on the PFC streams to stop in what is known as a PFC pause storm. Use the PFC watchdog to detect and to resolve PFC pause storms.

The PFC watchdog monitors PFC-enabled ports for PFC pause storms. The PFC watchdog intervenes when a PFC-enabled port receives PFC pause frames for an extended period of time and is unable to schedule any of the data packets on PFC-enabled queues. The PFC watchdog mitigates the situation by disabling the queue where the PFC pause storm was detected for a set length of time. This length of time, called the recovery time, is configurable. After the recovery time passes, the PFC watchdog reenables the affected queue.

The PFC watchdog plays a critical role with its three key functions: detection, mitigation, and restoration.

Benefits

  • Quickly detect and resolve PFC pause storms.

  • Maintain lossless traffic links.

  • Improve link quality.

Configuration

The watchdog recovery is a global setting, so it requires the same action on all ports to function. When you configure the PFC watchdog on multiple ports, make sure all ports are configured with the same type of action (drop or forward). By default, all ports use the drop action.

You can enable the PFC watchdog on all PFC-enabled queues.

The device logs PFC watchdog detection and recovery events in the system log with a timestamp.

  1. Enable PFC watchdog.
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    set class-of-service congestion-notification-profile cnp-name pfc-watchdog
  2. The PFC watchdog checks the status of PFC queues at regular intervals. Configure this interval in milliseconds.
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    set class-of-service congestion-notification-profile cnp-name pfc-watchdog watchdog-interval <1/10/100>
  3. Configure how many polling intervals the PFC watchdog waits before it mitigates the stalled traffic.
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    set class-of-service congestion-notification-profile cnp-name pfc-watchdog detection polling-interval
  4. Specify the action that the PFC watchdog takes to mitigate the traffic congestion.
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    set class-of-service congestion-notification-profile cnp-name pfc-watchdog watchdog-action <drop/forward>
  5. Configure how long the PFC watchdog disables the affected queue for before it restores PFC.
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    set class-of-service congestion-notification-profile cnp-name pfc-watchdog recovery time in milliseconds
  6. Verify you have configured the PFC watchdog correctly.
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    show class-of-service congestion-notification-profile cnp-name
  7. Monitor the number of PFC pause storms that have been detected and recovered, as well as the number of packets that have been dropped, on a particular interface.
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    show interfaces interface-name extensive

Platform Support

See Feature Explorer for platform and release support.

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