Question 1,646 of 1,420
mediumMultiple ChoiceObjective-mapped
CBWFQ and LLQ Queue Servicing Order and Configuration
Examine the following configuration:
policy-map QUEUE
class GOLD
bandwidth percent 25 queue-limit 64 packets
class SILVER
bandwidth percent 25 queue-limit 128 packets
class class-default
fair-queue
interface GigabitEthernet0/2
service-policy output QUEUE
Which statement about this configuration is true?
Quick Answer
The answer is that the GOLD class has a smaller queue limit than SILVER, which may cause more packet drops for GOLD traffic under congestion. This is true because while both classes are allocated the same bandwidth percentage of 25%, the GOLD class is configured with a queue-limit of only 64 packets, whereas SILVER can hold up to 128 packets. When congestion occurs, the smaller queue depth for GOLD means it will exhaust its buffer space sooner, leading to tail drops even though it is intended to be a higher-priority service. On the ENCOR 350-401 exam, this scenario tests your understanding of CBWFQ and LLQ queue servicing order and configuration, specifically that bandwidth allocation and queue limits are independent parameters—a common trap is assuming equal bandwidth guarantees equal drop behavior. Remember the memory tip: "Bandwidth shares the pie, queue limits define the plate size."
⚠ Common exam trap
Cisco often tests the misconception that a larger queue-limit implies more bandwidth, when in fact queue-limit only affects buffer depth and drop behavior, not bandwidth allocation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The GOLD class has a smaller queue limit than SILVER, which may cause more packet drops for GOLD traffic under congestion.
The GOLD class has a queue-limit of 64 packets, while the SILVER class has a queue-limit of 128 packets. Under congestion, the smaller queue for GOLD will fill up faster, leading to more tail drops for GOLD traffic, even though both classes are allocated the same bandwidth percentage. This demonstrates that queue-limit directly affects drop probability, not bandwidth allocation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The GOLD class has a smaller queue limit than SILVER, which may cause more packet drops for GOLD traffic under congestion.
Why this is correct
Correct. A smaller queue limit means fewer packets can be buffered, increasing the likelihood of drops when the queue is full.
- ✗
The SILVER class will always receive more bandwidth than GOLD because of its larger queue limit.
Why it's wrong here
Incorrect. Bandwidth allocation is determined by the 'bandwidth percent' command, not queue limit.
- ✗
The configuration is invalid because 'queue-limit' cannot be used with 'bandwidth percent' in the same class.
Why it's wrong here
Incorrect. They can be used together; 'queue-limit' sets the maximum number of packets in the queue.
- ✗
The 'fair-queue' command in class-default will override the bandwidth allocation for GOLD and SILVER.
Why it's wrong here
Incorrect. 'fair-queue' only applies to the default class and does not affect other classes.
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Same concept, more angles
2 more ways this is tested on 350-401
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Drag and drop the steps of CBWFQ and LLQ queue servicing order into the correct order, from first to last.
medium- ✓ A.Service the strict priority LLQ queue
- ✓ B.Check if LLQ queue is empty
- ✓ C.Service the next CBWFQ queue in WRR
- ✓ D.Apply bandwidth weight to each CBWFQ queue
- ✓ E.Drop packets from tail of congested queues
Why A: The correct queue servicing order for CBWFQ with LLQ is: first check if the LLQ queue is empty to determine if there is priority traffic; if the LLQ is not empty, service the strict priority LLQ queue to guarantee low latency. After servicing LLQ, apply bandwidth weights to each CBWFQ queue, then service the next CBWFQ queue in weighted round-robin (WRR). Finally, if congestion occurs, drop packets from the tail of congested queues. This order ensures priority traffic is handled first and other queues are serviced fairly.
Variation 2. Drag and drop the steps of CBWFQ and LLQ queue servicing order into the correct order, from first to last.
medium- ✓ A.Service the LLQ (priority queue)
- ✓ B.Service the first CBWFQ queue (highest bandwidth)
- ✓ C.Service the second CBWFQ queue (next bandwidth)
- ✓ D.Service the third CBWFQ queue (lower bandwidth)
- ✓ E.Service the default class queue
Why A: LLQ is serviced before any CBWFQ queues to ensure low-latency traffic. Within CBWFQ, queues are serviced in a weighted round-robin fashion based on bandwidth allocation. The default queue is serviced last.
Last reviewed: Jul 4, 2026
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