Quality of Service (QOS): 642-642 Exam
642-642 Questions & Answers
Exam Code: 642-642
Exam Name: Quality of Service (QOS)
Q & A: 100 Q&As
1: In an unmanaged CE router implementation, how does the service provider enforce the SLA?
A.by using class-based policing on the CE to PE link to limit the customer’s input rate
B.by marking on the CE to PE link and using CBWFQ and CB-WRED on the PE to P link
C.by marking on the CE to PE link and using class-based policing on the PE to P link
D.by using class-based random discard on the CE to PE link to limit the customer’s input rate
Correct Answers: A
2: In a typical converged campus network, which two of the following are considered QoS best
practices? (Choose two.)
A.Traffic classification and marking is performed as close to the traffic source as possible.
B.Traffic classification and marking is performed at the high speed core layer.
C.Ensure voice traffic is serviced by a weighted fair queue.
D.Only a reasonable number of applications should be classified into the mission-critical traffic
E.NBAR is used at the high speed core layer to discover and classify network applications.
F.Catalyst switches should use weighted round robin (WRR) queuing giving the voice traffic the
Correct Answers: A D
3: What are two benefits of WFQ? (Choose two.)
A.WFQ is very easy to configure, and no manual traffic classification is necessary.
B.WFQ can provide fixed-bandwidth and fixed-delay guarantees.
C.WFQ can provide fixed-bandwidth guarantees.
D.WFQ can provide fixed-delay guarantees.
E.WFQ prevents the large-volume flows with large packet size from starving out the low-volume
flows with small packet size.
F.Based on DSCP, WFQ allows weighted, random dropping of packets when the WFQ system is
Correct Answers: A E
6: Based on the following 2950 switch configurations, which statement is correct?
no wrr-queue cos-map
wrr-queue bandwidth 20 10 70 1
wrr-queue cos-map 4 5
wrr-queue cos-map 1 0 1 2 3
wrr-queue cos-map 3 6 7
A.Queue 1 is setup as the expedite queue.
B.Queue 2 is setup as the expedite queue.
C.Queue 3 is setup as the expedite queue.
D.Queue 4 is setup as the expedite queue.
E.No queue is setup as the expedite queue.
Correct Answers: E
7: Refer to the exhibit. A typical configuration involving an IP phone with an attached PC is
shown. According to QoS recommendations, at which demarcation line (shown as dotted lines)
would the trust boundary normally exist?
Correct Answers: B
8: Which technology is required when configuring FRF.12 on a Cisco device?
D.MLP with interleaving
Correct Answers: E
9: The following commands have been configured under the fa0/1 interface on the 2950 switch:
wrr-queue bandwidth 20 1 80 0
mls qos trust cos
mls qos trust device cisco-phone
Voice traffic from the IP phone that is directly connected to the fa0/1 interface is experiencing
excessive delays. What could be the cause of this problem?
A.The wrr-queue bandwidth weightings are not correct.
B.The default wrr-queue cos-map is being used.
C.The default cos-to-dscp map is being used.
D.The default dscp-to-cos map is being used.
E.The trust boundary configuration is not correct.
Correct Answers: B
10: Based on the configuration, which two statements are true? (Choose two.) A.The interactive traffic class will have a minimum bandwidth guarantee of 256 kbps.
B.The interactive traffic class will have a maximum bandwidth guarantee of 256 kbps.
C.If the interactive traffic class exceeds an average rate of 256 kbps, the traffic rate will be
throttled down to 128 kbps.
D.This configuration allows class-based traffic shaping to lower the traffic rate in response to the
E.The interactive traffic class will have a min-rate (min-cir) of 128 kbps.
Correct Answers: D E
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