792 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections

Example 4-10 Exhibit for CBWFQ Configuration Questions (Continued)

class class1 priority 60 policy-map pmap2 class class2 priority 60 policy-map pmap3 class class3 priority 60 policy-map pmap4 class class4 priority 60 policy-map pmap5 class class5 priority 60

!

interface Serial0/0 service-policy output ?????

!

access-list 101 permit udp any gt 16383 any gt 16383

access-list 102 permit udp any range 16383 32767 any range 16383 32767

!

All the policy maps except pmap4 would perform LLQ on voice payload. In some cases, the policy map would match more than just voice payload. Only pmap1 would match just RTP voice payload traffic.

30Using the same exhibit as in the preceding example, describe what must also be true for pmap4 to queue voice payload traffic successfully, and only voice payload traffic, in a lowlatency queue.

If some other classification and marking tool were configured, and it marked all voice payload traffic as DSCP EF, pmap4 would match all voice packets in the lowlatency queue.

Comparing Queuing Tool Options

31Which of the following queuing tools allows for WRED inside a single queue? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

CBWFQ.

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32Which of the following queuing tools can always service a particular queue first, even when other queues have packets waiting? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

PQ, LLQ, and IP RTP Priority.

33Which of the following queuing tools allows for a percentage bandwidth to be assigned to each queue? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

CBWFQ and LLQ. CQ effectively does this as well, but you cannot specify the exact percentage.

34Which queuing tools could be configured to provide the lowest possible latency for voice traffic? Of these, which does Cisco recommend as the best option for voice queuing today?

PQ, IP RTP Priority, and LLQ. PQ would probably not be a good option in many networks today, but it could provide the lowest possible latency for voice. Cisco currently recommends LLQ.

35Which of the following queuing tools can use flow-based classification? First-In, FirstOut Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

WFQ and CBWFQ in the class-default queue.

36Which of the following queuing tools uses the Modular QoS CLI? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

CBWFQ, LLQ.

37Which of the following queuing tools allows for a value to be configured, which then results in a specific number of bytes being taken from each queue during a round-robin pass through the queues? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

CQ.

38Which of the following queuing tools allow the largest number of queues for a flow-based tool? For a class-based tool? What are the maximum values? First-In, First-Out Queuing (FIFO); Priority Queuing (PQ); Custom Queuing (CQ); Weighted Fair Queuing (WFQ); Class-Based WFQ (CBWFQ); Low Latency Queuing (LLQ); and IP RTP Priority.

WFQ allows 4096 (flow based), and CBWFQ allows 64 queues (class based).

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Policing with CAR and CB Policer

5List the command, with the correct syntax, that sets a policed rate of 512 kbps, a Bc of 1 second’s worth of traffic, and a Be of an additional 0.5 second’s worth of traffic, when using CAR. Do not assume any defaults; explicitly set the values in the command. You can choose any other settings needed for the command.

rate-limit input 512000 64000 96000 conform-action transmit exceed-action drop

6Which policing tools allow for three categories of actions to take?

CB policer.

7Explain the concept behind re-marking policed packets versus discarding the packets.

By re-marking the packets, you can increase the packet’s likelihood of being dropped later. For instance, WRED reacts to the precedence or DSCP value, discarding certain marked values more aggressively. By re-marking, if no congestion occurs, the packet may still get through the network. If congestion does occur, the packet that the policer marked down has a greater chance of being dropped.

8CB policing has been configured under subinterface s0/0.1. What show command lists statistics for CB policing behavior just for that subinterface?

show policy-map interface s0/0.1

Shaping with FRTS, GTS, DTS, and CB Shaping

9Along with the class-map, policy-map, and service-policy commands, CB shaping requires one specific command that actually sets values used for the shaping function. List the command, with the correct syntax, that sets a shaped rate of 128 kbps, a Bc of 8000, and a Be of 8000, when using CB shaping. Do not assume any defaults; explicitly set the values in the command.

shape 128000 8000 8000

10Compare and contrast the use of the class-map and map-class commands in terms of how each is used by FRTS and CB shaping.

FRTS uses map-class to create a common set of shaping parameters, which are then applied to an interface, subinterface, or VC. FRTS does not use the class-map command for shaping. Likewise, CB shaping does not use the map-class command. It does, however, use the class-map command for defining classification options. Interestingly, FRTS can use the class-map command indirectly, when using CBWFQ or LLQ. (See Example 5-9 later in the book for a sample configuration.)

11DTS has been configured under subinterface s0/0.1. What show command displays statistics for DTS behavior just for that subinterface?

show policy-map interface s0/0.1