Quality of Service (QOS): 642-642 Exam
- 642-642 Questions & Answers
- Exam Code: 642-642
- Exam Name: Quality of Service (QOS)
- Updated: February 2, 2012
- Q & A: 100 Q&As
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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 class.
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 highest priority.
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 full.
Correct Answers: A E
4: LAB
Correct Answers: R1>en
R1#conf t
R1(config)#policy-map llq-policy
R1(config-pmap)#class VOICE
R1(config-pmap-c)#priority 168
R1(config-pmap-c)#exit
R1(config-pmap)#class interactive
R1(config-pmap-c)#bandwidth 30
R1(config-pmap-c)#exit
R1(config-pmap)#class bulk
R1(config-pmap-c)#bandwidth 16
R1(config-pmap-c)#shape average 24000
R1(config-pmap-c)#exit
R1(config-pmap)#class class-default
R1(config-pmap-c)#fair-queue
R1(config-pmap-c)#exit
R1(config)#int s0/0
R1(config-if)#service-policy output llq-policy
R1(config-if)#end
R1#copy run start
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?
A.A
B.B
C.C
D.D
Correct Answers: B
8: Which technology is required when configuring FRF.12 on a Cisco device?
A.FRF11.c
B.FRF.8
C.VoFR
D.MLP with interleaving
E.FRTS
F.WRED
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 BECN bit.
E.The interactive traffic class will have a min-rate (min-cir) of 128 kbps.
Correct Answers: D E
11: Refer to the exhibit. Which three statements are true about the configuration? (Choose three.)
A.Traffic that is subject to shaping can burst up to 32,000 bps.
B.IP traffic (DSCPs 5, 6, and 7) that is sent on fastethernet 0/0 will be traffic policed.
C.RTP traffic (ports 2024 and 1000) that is sent on fastethernet 0/0 will be traffic shaped.
D.Traffic that is subject to policing will have the DCSP set to 0 if the rate exceeds 1000 bps.
E.IP traffic (DSCPs 1, 2, 3, and 4) that is sent on fastethernet 0/0 are considered to have a violate status and are dropped.
F.IP traffic (DSCP 0) that is sent on fastethernet 0/0 will be subject to fair queuing.
Correct Answers: A B F
12: Which command is needed to correct the following configurations in order to enable ppp multilink LFI on the s0/0 interface?
interface Serial0/0
ip address 10.1.1.1 255.255.255.0
encapsulation ppp
no fair-queue
ppp multilink
multilink-group 2001100114
!
interface Multilink2001100114
bandwidth 384
ip address 10.1.1.1 255.255.255.0
service-policy output AutoQoS-Policy-UnTrust
ppp multilink
ppp multilink fragment-delay 10
ppp multilink interleave
A.the no ip address command on the s0/0 interface
B.the multilink-group 2001100114 command on the Multilink2001100114 interface
C.the ppp multilink load-threshold command on the s0/0 interface
D.the ppp multilink load-threshold command on the Multilink2001100114 interface
E.the ppp multilink interleave command on the s0/0 interface
Correct Answers: A
15: Which three characteristics are drawbacks to the use of a best-effort with over-provisioning backbone design? (Choose three.)
A.The design costs more to implement than a DiffServ backbone.
B.Denial of Service attacks on one service can affect all network traffic.
C.The design uses a different over-provisioning ratio for the different traffic classes.
D.It requires complex QoS mechanisms at the network edge.
E.It requires complex QoS mechanisms at the network core.
F.Unplanned network failures can cause unexpected congestion in the network.
Correct Answers: A B F
16: In a managed CE scenario, the customer’s network is supporting VoIP and bulk file transfers. According to the best practices, which QoS mechanisms should be applied on the WAN edge CE-PE 56-kbps Frame Relay link on the CE outbound direction?
A.WRR, FRTS, FRF.12, and CB-RTP header compression
B.WRR, CB-WRED, CB-Marking, FRF.12, and CB-RTP header compression
C.CBWFQ, CB-WRED, CB-Marking, CB-Policing, and FRTS
D.CBWFQ, FRTS, FRF.12, and CB-RTP header compression
E.LLQ, CB-WRED, CB-Marking, FRTS, FRF.12, and CB-RTP header compression
F.LLQ, CB-WRED, CB-Policing, and CB-TCP and CB-RTP header compressions
Correct Answers: E
17: Which QoS mechanism adds IP Precedence information for prefixes into the FIB table?
A.QoS pre-classify
B.AutoQoS
C.QPPB
D.Class-Based Marking
E.LLQ
F.Class-Based WRED
Correct Answers: C
18: LAB
Correct Answers: Please click console
2950-SWITCH>en
2950-SWITCH#config terminal
2950-SWITCH(config)#int fa0/1
2950-SWITCH(config-if)#mls qos trust dscp
2950-SWITCH(config-if)#exit
2950-SWITCH(config)#int fa0/11
2950-SWITCH(config-if)#mls qos trust cos
2950-SWITCH(config-if)#exit
2950-SWITCH(config)#int fa0/10
2950-SWITCH(config-if)#mls qos trust cos
2950-SWITCH(config-if)#mls qos trust device cisco-phone
2950-SWITCH(config-if)#exit
19: What does the following command accomplish?
router(config-pmap-c)# shape fecn-adapt
A.enables the router to lower the shaping rate when BECN bits are received
B.enables the router to lower the shaping rate when FECN bits are received
C.enables the router to respond to FECN bits by creating test frames in the opposite direction with the BECN bit set
D.enables the router to respond to BECN bits by creating test frames in the opposite direction with the FECN bit set
E.enables the router to increase the shaping rate when BECN bits are received
F.enables the router to increase the shaping rate when FECN bits are received
Correct Answers: C
20: What will be the peak shape rate based on the configuration that follows?
policy-map setpeak
class all-traffic
shape peak 32000
A.16000 bps
B.32000 bps
C.48000 bps
D.64000 bps
E.80000 bps
F.96000 bps
Correct Answers: D