A network administrator configures a Cisco router WAN egress interface with a Modular QoS … — Cisco CCNA

A network administrator configures a Cisco router WAN egress interface with a Modular QoS CLI (MQC) policy map. The policy assigns real-time Voice over IP (VoIP) traffic to a class using the `priority 512` command, while transactional data is assigned to a class using the `bandwidth 2048` command. During a period of interface congestion, incoming voice traffic spikes to $768\text{ kbps}$ . Which statement accurately describes how the router handles the voice traffic that exceeds the $512\text{ kbps}$ allocated threshold?

A
The router buffers the excess $256\text{ kbps}$ of voice packets in memory and delays their transmission until link congestion clears.
The router drops the excess $256\text{ kbps}$ of voice traffic using a built-in strict priority policer to prevent starving other bandwidth-guaranteed queues.Answer
C
The router transmits all $768\text{ kbps}$ of voice traffic immediately because strict priority queues override all configured bandwidth limits during congestion.
D
The router automatically remarks the excess $256\text{ kbps}$ of voice traffic to a lower DSCP value and forwards it into the default class queue.

Answer

The router drops the excess voice traffic exceeding the

512\text{ kbps}

threshold using a built-in policing mechanism to protect other queues from bandwidth starvation during congestion.

Low Latency Queuing (LLQ) uses the `priority` command to create a strict priority queue for delay-sensitive traffic such as voice. To prevent a rogue stream or burst of voice traffic from starving other queues (configured via `bandwidth` statements) during link congestion, LLQ applies a built-in policer to the priority queue. Traffic offered to the priority queue up to the configured limit (

512\text{ kbps}

) is serviced ahead of all other queues. Any excess traffic beyond

512\text{ kbps}

during congestion is dropped by the policer.

Step-by-Step Solution

Identify the QoS queuing feature configured by the `priority` command.

The `priority` command configures Low Latency Queuing (LLQ), creating a strict priority queue alongside Class-Based Weighted Fair Queuing (CBWFQ) classes.

LLQ provides strict priority servicing for delay-sensitive traffic like voice.

Analyze how LLQ behaves when traffic in the priority queue exceeds its allocated bandwidth during interface congestion.

To prevent strict priority traffic from monopolizing the interface and starving CBWFQ classes, LLQ implements an implicit policer built into the priority queue.

Without policing, priority traffic could burst endlessly and cause complete packet drop/starvation in other classes.

Determine the action taken on the

256\text{ kbps}

burst exceeding the

512\text{ kbps}

limit.

The internal policer drops all incoming voice traffic that exceeds

512\text{ kbps}

while congestion persists.

Policing drops out-of-profile packets immediately rather than buffering them.

Key Concept

Low Latency Queuing (LLQ) Priority Queue Policing

Estimated Time:2m 0s

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