CCNP Voice FAQ: Congestion Management and Queuing
Q1. Which of the following is not a common reason for congestion?
A. Speed mismatch
Q2. Which of the following is a congestion management tool?
D. Fast Reroute
Q3. Which of the following is not a function within a queuing system?
A. Creating one or more queues
C. Assigning arriving packets to queues
D. Scheduling departure of packets from queues
Q4. How many queuing subsystems exist in an interface queuing system?
B. Two: a software queue and a hardware queue
C. Three: a software, a transmit, and a hardware queue
D. Four: a software, a hold, a transmit, and a hardware queue
Q5. What is the default queuing discipline on all but slow serial interfaces?
Q6. How many queues does PQ have?
B. Two: High and Low
C. Three: High, Medium, and Low
D. Four: High, Medium, Normal, and Low
Q7. Custom queuing is a modified version of which queuing discipline?
Q8. Which of the following is not a goal or objective of WFQ?
A. Provide high bandwidth to high-volume traffic
B. Divide traffic into flows
C. Provide fair bandwidth allocation to the active flows
D. Provide faster scheduling to low-volume interactive flows
Q9. Which of the following is not used to recognize and differentiate flows in WFQ?
A. Source and destination IP address
B. Packet size
C. Source and destination TCP/UDP port number
D. Protocol number and type of service
Q10. Which of the following is an advantage of WFQ?
A. WFQ does not starve flows and guarantees throughput to all flows.
B. WFQ drops/punishes packets from most aggressive flows first.
C. WFQ is a standard queuing mechanism that is supported on most Cisco platforms.
D. All of the above.
Q11. Which of the following is not a disadvantage of WFQ?
A. WFQ does not offer guarantees such as bandwidth and delay guarantees to traffic flows.
B. FQ classification and scheduling are not configurable and modifiable.
C. You must configure flow-based queues for WFQ, and that is a complex task.
D. Multiple traffic flows may be assigned to the same queue within the WFQ system.
Q12. Which of the following is not true about CBWFQ?
A. CBWFQ allows creation of user-defined classes.
B. CBWFQ allows minimum bandwidth reservation for each queue.
C. CBWFQ addresses all of the shortcomings of WFQ.
D. Each of the queues in CBWFQ is a FIFO queue that tail drops by default.
Q13. Which of the following is not true about LLQ?
A. LLQ includes a strict-priority queue.
B. The LLQ strict priority queue is given priority over other queues.
C. The LLQ strict-priority queue is policed.
D. LLQ treats all traffic classes fairly.
Q14. Why does congestion occur?
Q15. Define queuing.
Q16. What are three main tasks that congestion management/queuing mechanisms might perform?
Q17. What is the default queuing algorithm on Cisco router interfaces?
Q18. In what situation might FIFO be appropriate?
Q19. Describe priority queuing.
Q20. Cisco custom queuing is based on which queuing mechanism?
Q21. What are the Cisco router queuing components?
Q22. List the steps that a packet takes when it goes through an interface queuing system.
Q23. Describe WRR queuing.
Q24. Describe WFQ and its objectives.
Q25. How does WFQ define traffic flows?
Q26. Describe WFQ early dropping and aggressive dropping.
Each flow-based queue within WFQ has a congestive discard threshold (CDT). If a packet arrives and the hold queue is not full but the CDT of that packet flow queue is reached, the packet is dropped. This is called WFQ early dropping.
Q27. What are the benefits and drawbacks of WFQ?
Benefits: Configuring WFQ is simple and requires no explicit classification, WFQ does not starve flows and guarantees throughput to all flows, and WFQ drops packets from most aggressive flows and provides faster service to nonaggressive flows.
Drawbacks: WFQ classification and scheduling are not configurable and modifiable, WFQ does not offer guarantees such as bandwidth and delay guarantees to traffic flows, and multiple traffic flows might be assigned to the same queue within the WFQ system.
Q28. What are the default values for CDT, dynamic queues, and reservable queues?
Q29. How do you adjust the hold queue size?
Q30. List at least two problems associated with PQ/CQ/WFQ.
Q31. Describe CBWFQ.
Q32. What are the three options for bandwidth reservation within CBWFQ?
Q33. How is available bandwidth calculated?
Available bandwidth = (interface bandwidth x maximum reserved bandwidth) × (sum of all existing reservations)
Q34. What are the benefits and drawbacks of CBWFQ?
Q35. How is CBWFQ configured?
Q36. Describe low-latency queuing.
Q37. What are the benefits of LLQ?
Q38. How do you configure LLQ?
queue(s), instead of using the keyword/command bandwidth, you use the keyword/command priority within the desired class of the policy map.