Queue Drops Alert

The Queue Drops alert is generated when packets are dropped from one or more queues on a switch interface due to congestion. Classic Central continuously monitors queue utilization and packet drop rates to detect traffic handling issues that may impact application performance.

By default, the alert is triggered when 5% or more packets are dropped in a specific queue and the overall port utilization exceeds 5% for at least 5 minutes. The alert is raised with Major severity. Queue drops typically indicate congestion, improper traffic distribution, or QoS misconfiguration.

Alert Triggering and Clearing Conditions

• Triggering Condition—Queue packet drops are ≥ 5%, and Overall port utilization is > 5% for at least 5 minutes.

• Clearing Condition—The alert automatically clears when the packet drop percentage falls below the configured threshold.

Common Causes

Queue drops may occur due to the following reasons:

• Traffic not being evenly distributed across queues.

• Missing or incorrect DSCP/PCP-to-queue mappings.

• Interface oversubscription.

• Microbursts or sudden traffic spikes.

• Inadequate or misconfigured QoS policies.

• Multiple ingress ports forwarding traffic to a lower-bandwidth egress port.

• Excessive broadcast or multicast traffic.

Alert Behavior

When a Queue Drops alert is triggered:

• Classic Central evaluates queue-level statistics on the affected interface.

• The alert is integrated with Switch Health for centralized visibility.

• Impacted interfaces are highlighted in the Wired Interfaces card and Faceplate view.

• Queue utilization, packet pass or drop statistics, and throughput data are available in the expanded alert view.

• The Root Cause and Action section provides configuration-based recommendations to mitigate congestion.

• Summary Card

  The Summary card provides a concise overview of the alert, including:

  • Affected device, interface, and queue number.

  • Packet drop percentage observed during the evaluation window.

  • First occurred, last occurred, and duration of the alert.

  • Number of occurrences Priority of the alert Interface properties such as speed, duplex, MTU, VLAN, and connector type.

    This information helps quickly assess the scope, severity, and persistence of the issue.

• Action Card (Root Cause and Actions)

  The Action card provides probable root causes and recommended remediation steps, such as:

  • Possible root causes.

  • Traffic directed to a single queue due to missing or incorrect QoS configuration.

  • Interface over subscription or micro-bursts.

  • Multiple ingress ports forwarding traffic to a lower-bandwidth egress port.

  • Excessive broadcast or multicast traffic.

Recommended Actions

When you receive a Port Flap alert:

• Verify that traffic is evenly distributed across queues and that DSCP/PCP-to-queue mappings are correctly configured.

• Review and adjust QoS policies to ensure appropriate queue assignment.

• Configure an appropriate queue profile to allocate sufficient buffer space.

• Review queuing and scheduling behavior (for example, WRR or strict priority) and adjust as needed.

• Check for network loops or traffic flooding that may lead to oversubscription.

• Monitor queue statistics after changes to confirm that packet drops are reduced.

Related Events

The alert is associated with queue-level packet drop events observed on the affected interface.

Additional Notes

Queue Drops alerts are generated per interface. Alerts may automatically clear once packet drops fall below the threshold. Sustained queue drops can degrade application performance and user experience and should be addressed promptly.