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QUESTION 124
What is a notable problem with weighted round-robin (WRR) queuing?
A. improper bandwidth allocation
B. no traffic prioritization
C. queue starvation
D. difficult implementation
Correct Answer: A Section: (none) Explanation Explanation/Reference:
Explanation: Keep in mind that each port has a finite amount of buffer space to support the buckets. One queue will take all of the buffer space, for instance, two queues will divide the buffer space into two parts, three queues divide the buffer space into three parts, and so on. If the buffer space is too small, it will not be effective in momentarily holding the traffic before transport. Because nonpriority queues are serviced in either a round-robin or a Weighted Round-Robin manner, there is no guearantee that the traffic in the buffer is transported next. This limitation can lead to instaneous buffer overrun.
QUESTION 125
In most VPN tunneling, what is the classic QoS problem?
A. VPN overhead eliminates QoS processing time.
B. VPN adds too much delay to be used for voice.
C. The QoS information is encrypted in the packet being tunneled.
D. The QoS information is removed in the encryption process.
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
QUESTION 126
How does explicit congestion notification (ECN) work with Weighted Random Early Detection (WRED)?
A. ECN provides an additional marking option to WRED when the number of packets in queue is between the minimum and maximum thresholds.
B. ECN is an extension to WRED that provides support non-WRED devices.
C. ECN removes the tail-drop mechanism form WRED and replaces it with a dual leaky-bucket, congestion-management mechanism.
D. ECN applies the mark probability denominator to all packets identified in the class-map.
Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: As with RED, WRED monitors the average queue depth in the router and determines when to begin packet drops based on the queue depth. When the average queue depth crosses the user-specified “minimum threshold, ” WRED begins to drop packets (both TCP and UDP) with a certain probability. If the average queue depth ever crosses the user-specified” maximum threshold, ” then WRED reverts to “tail drop, ” where all incoming packets might be dropped. The idea behind using WRED is to maintain the queue depth at a level somewhere between the minimum and maximum thresholds, and to implements different drop policies for different classes of traffic. Reference: Introduction to IP QoS p.5-15
QUESTION 127
How does NBAR differ from traditional TCP/UDP packet recognition?
A. NBAR queries each application directly
B. NBAR uses different port numbers than TCP/UDP
C. NBAR builds a database of packet types
D. NBAR looks into the payload for application clues
Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Page 185, IP Telephony Self-Study Cisco DQOS Exam Certification Guide, http//www.ciscopress.com/ title/1587200589
QUESTION 128
DRAG DROP
Drag the correct description to the correct implementation model.
A.
B.
C.
D.
Correct Answer: Section: (none) Explanation
Explanation/Reference:
Explanation: 1) Best-effort. The Internet was designed for best-effort, no-guarantee delivery of packets. This behavior is still predominant in today’s Internet. 2) Integrated Services model. Introduced to supplement the best-effort delivery by setting aside some bandwidth for application that require bandwidth and delay guarantees. The Integrated Services model expects application to signal their requirements to the network. Resource Reservation Protocol (RSVP) is used to signal QoS requirements to the network. 3) Differentiated Services model. Added to provide more scalability in providing QoS to IP packets. The main difference is that the network recognizes packets (no signalling is needed) and provides the appropriate services to them. Reference: Introduction to IP QoS p.18
QUESTION 129
Compressed Real-time Transport Protocol compresses the 40 byte IP/UDP/RTP header down to what size?
A. Usually 1 or 2 bytes
B. Usually 2 or 4 bytes
C. Usually 4 or 8 bytes
D. Usually 8 or 16 bytes E. It varies based on the information contained in the header.
Correct Answer: B Section: (none) Explanation
Explanation/Reference:
QUESTION 130
Which RED packet drop mode is used when the average queue size has reached or exceeded its maximum?
A. no drop
B. tail drop
C. random drop
D. full drop
Correct Answer: B Section: (none) Explanation
Explanation/Reference:
Page 435, IP Telephony Self-Study Cisco DQOS Exam Certification Guide, http//www.ciscopress.com/ title/1587200589
QUESTION 131
Which of the tools mentioned below will you find most helpful when designing or managing QoS? (Choose all that apply.)
A. CPC
B. QDM
C. IPM
D. CAC
E. QPM
F. SMS
G. All of the above
Correct Answer: BCEF Section: (none) Explanation
Explanation/Reference:
Explanation:
These four are management tools which Cisco provides to assist in managing the QoS policies and
configuration in a network.
Reference: DQOS Exam Certification Guide p.102, 103
QUESTION 132
The QoS design and implementation process comprises of the following steps:
1.
characterize network
2.
implement policy
3.
determine customer priorities/QoS policy
4.
monitor network
What is the correct order for these steps?
A. 4, 1, 3, 2
B. 1, 3, 2, 4
C. 3, 1, 2, 4
D. 1, 2, 3, 4
E. 4, 3, 1, 2
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: The process begins with determining priorities – what traffic should get more bandwidth? Less loss, jitter, and delay? The policies, however, typically define classes of traffic in general terms; you need to know the specific of the traffic patterns so that you can configure the QoS tools to classify the traffic correctly. At Step 2, you characterize the traffic, which enables you to know how to configure the various classification features of the QoS tools. Then you can proceed with Step3, where you actually configure the QoS tools. Finally, you ceed to monitor the network (Step 4) to determine whether you met the stated policy goals you determined in Step 1. The process continues over time, with the quality of the QoS implementation improving with each cycle. Reference: DQOS Exam Certification Guide p.669
QUESTION 133
Within a distributed call processing environment, what can you use to achieve call admission control across the WAN?
A. You can use a 720VXR to diversify the IPN1 traffic.
B. You can use a CiscoWorks RME package to keep lines clear.
C. You can use a gatekeeper.
D. You can use a H.333 Line card.
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
QUESTION 134
Which features can be used to police traffic according to the Cisco QoS Framework?
A. CQ
B. LLQ
C. CAR
D. NBAR
E. WRED
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: Only a few remaining mechanisms have marking capabilities: 1) Committed Access Rate (CAR), which is used for traffic policing 2) Class-based Policing, which is also used for traffic policing 3) Class-based Marking, which is used for classification and marking purposes only. It may however be combined with other mechanisms available with the Modular QoS CLI Reference: Introduction to IP QoS
QUESTION 135
What are the advantages of making use of NBAR as part of a classification and marking design? (Choose all that apply.)
A. It is able to match any TCP or UDP port number.
B. It is able to match packets based on application layer information
C. It has the ability to match QoS, Precedence, pr DSCP using NBAR.
D. It has the ability to match packets that are difficult to match with access lists.
E. All of the above.
Correct Answer: BD Section: (none) Explanation
Explanation/Reference:
Explanation:
NBAR can be used to look beyond layer 4 port numbers and inspect the actual payload. Also NBAR can
be used to easily identify data which can be hard to configure access lists.
DQOS course notes:
NBAR can classify static port protocols. Although access control lists (ACL’s) can also be used for this
purpose, NBAR is easier to configure and can provide classification statistics that are not available when
using ACL’s.
Reference:
http://www.cisco.com/en/US/products/sw/iosswrel/ps5012/products_feature_guide09186a0080134add
QUESTION 136
Which two interface commands will enable precedence-based WRED when configuring WRED without using the MQC?
A. wred
B. random-detect prec-based
C. service-policy random-detect
D. random-detect
E. wred prec-based
Correct Answer: BD Section: (none) Explanation
Explanation/Reference:
Explanation:
Random-detect command:
1) Enables IP precedence basid WRED
2) Default service profile is used
3) Non-distributed WRED cannot be combined with fancy queuing – FIFO queuing has to be used.
4) WRED can run distributed on VIP-based interfaces (dWRED)
5) dWRED can be combined with dWFQ
Random-detect precedence command:
1) Changes RED profile for specified IP precedence value
2) Packet drop probability at maximum threshold is 1/mark-prob/dominator
3) Non-wieghted RED is achieved by using the same RED profile for all precedence values.
Reference: Introduction to IP QoS p.5-22, 5-23
QUESTION 137
Which IOS features will you advice the new Certkiller trainee technician to use to combat the effects of global synchronization? (Choose all that apply.)
A. GTS
B. LLQ
C. FRED
D. WRED
E. RSVP F. WFQ
Correct Answer: CD Section: (none) Explanation
Explanation/Reference:
Explanation:
Weighted RED (WRED) and Flow-Based WRED (FRED) are the two congestion-avoidance tools available
in IOS.
QUESTION 138
The newly appointed Certkiller trainee wants to know which Cisco IOS congestion avoidance features use IP Precedence to affect the probability of whether or not a packet will be dropped. What will your reply be? (Choose all that apply.)
A. CAR
B. RED
C. FRED
D. WRED
E. NBAR
F. WFQ
Correct Answer: CD Section: (none) Explanation
Explanation/Reference:
QUESTION 139
The newly appointed Certkiller trainee wants to know which Cisco IOS congestion avoidance features specifically penalizes flows (such as UDP) that does not respond to drops. What will your reply be?
A. IP RTP priority
B. RED
C. WFQ
D. FRED
E. NBAR
F. WRED
Correct Answer: AD Section: (none) Explanation
Explanation/Reference:
Not D: WRED is not sensitive to flows.
QUESTION 140
Which of the following show commands will list the settings and counters for WRED behavior when you configure WRED using MQC?
A. show wred
B. show policy
C. show interface s0 random
D. show wred interface policy
E. show policy wred
F. show wred policy
Correct Answer: B Section: (none) Explanation
Explanation/Reference:
Not C: There is no command show interface s0 random
QUESTION 141
Exhibit: interface Fddi2/1/0 rate-limit input access-group rate-limit 100 8000000 80000 conform-action transmit exceed-action drop ip address 200.200.6.1 255.255.255.0 ! access-list rate-limit 100 00e0.34b0.7777 What is the result of the configuration shown in the exhibit on input traffic to the FDDI interface?
A. All input traffic on the FDDI interface is rate limited to 80 Mbps.
B. Traffic from MAC address 00e0.34b0.7777 is rate limited to 80 Mbps.
C. Traffic sent to the FDDI interface is dropped if it exceeds a rate of 512,000 bps.
D. Traffic sent from the MAC address 00e0.34.b0.7777 is dropped if it exceeds a rate of 512,000 bps
E. All traffic sent to the FDDI interface is accepted at 100 Mbps as long as it conforms to the excessive burst parameter.
Correct Answer: B Section: (none) Explanation
Explanation/Reference:
QUESTION 142
Which command is used on Cisco IOS routers to enable Flow based WRED (FRED)?
A. router#(config)flow enable
B. router#(config)random detect
C. router#(config-if)flow enable
D. router#(config)random detect flow
E. router#(config-if)random detect flow
Correct Answer: E Section: (none) Explanation
Explanation/Reference:
Explanation:
To enable flow-based WRED, use the ramdom-detect flow interface configuration command.
You must use this command to enable flow-based WRED before you can use the random-detect flow
average-depth-factor and ramdom-detect flow count commands to further configure the parameters of low-
based WRED.
Reference: Introduction to IP QoS p.5-44
QUESTION 143
How do you enable PGM on Cisco routers?
A. Router#(config) ip pgm
B. Router#(config) set pgm
C. Router#(config) ip pgm router
D. Router#(config-if) ip pgm router
E. Router#(config-if) ip pgm enable
Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation: To enable Pragmatic General Multicast (PGM) Router Assist and thereby allow PGM to operate more efficiently on the router, use the ip pgm router interface configuration command. To disable PGM Router Assist for the interface, use the no form of the command. ip pgm router no ip pgm router Reference: http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/ products_command_reference_chapter09186a00
QUESTION 144
What is the main purpose of the Cisco IOS QPPB feature?
A. It provides flow-based WRED support to External BGP peers.
B. QPPB enables traffic shaping on BGP enabled WAN interfaces.
C. It conveys IP Precedence or QoS Group to destinations using BGP communities.
D. It allows non-CEF enabled routers to support QoS and BGP by tagging routes in the BGP table.
E. It provides QoS policy in BGP networks by allowing centralized QoS configuration confederations.
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
QoS Policy Propagation through BGP is a mechanism that can be split into two parts:
1) Policy propagation via BGP, where a QoS policy is encoded into a BGP attribute. BGP Communities are
typically used to encode a QoS policy.
2) Marking of packets with IP precedence or QoS group based on the QoS policy learned via BGP.
BGP Policy is usually set on ingress routers (ingress for route propagation, egress for packet forwarding)
in an Autonomous System. BGP then carries the information to other routers in the AS and translates
(using a route map) this information into IP precedence or QoS group. Marking is then enabled on per-
interface basis.
Reference: Introduction to IP QoS p.2-23
QUESTION 145
What is the purpose of shaping traffic conditioners in IP QoS?
A. Shaping reorders transmit queues to offer priority service to specific traffic flows.
B. Shaping is a non-buffer based solution that drops packets above a specified burst rate.
C. Shaping techniques monitor network traffic loads in an effort to anticipate and avoid congestion.
D. Shaping uses packet re-write capabilities to sort traffic and maintain specific data rates for classified traffic.
E. Shaping avoids delays by smoothing out speed mismatches in the network and by limiting transmission rates.
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
If the traffic exceeds the contract, one option is to shape the traffic. Shaping just means to buffer or queue
the traffic, slowing it down, so that the resulting sending rate is withing the contract. Reference: DQOS Exam Certification Guide p.130
QUESTION 146
When configuring Weighted Random Early Detection (WRED), what is a potential problem that could arise if the difference between the maximum threshold and the minimum threshold is too small?
A. Too many packets could be dropped resulting in global synchronization.
B. The network could become overly congested because not enough packets are dropped as traffic levels increase.
C. The only effect of these settings is that traffic utilization peaks are greatly reduced as smaller amounts of traffic are offered to the network.
D. This condition could never occur as the Cisco IOS forces users to configure a minimum distance setting between both the minimum and maximum threshold.
E. The WRED mechanism might not recognize the maximum threshold has been hit if it is configured too close to the minimum threshold. The result would be unmanaged congestion.
Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: The probability of a packet being dropped is based on three configurable parameters: 1) Minimum threshold – When the average queue depth is above the minimum threshold, RED starts dropping packets. The rate of packet drop increases linearly as the average queue size increases, until the average queue size reaches the maximum threshold. 2) Maximum threshold – When the average queue size is above the maximum threshold, all packets are dropped. If the difference between the maximum threshold and the minimum threshold is too small, many packets might be dropped at once, resulting in global synchronization. 3) Mark probability denominator – This is the fraction of packets dropped when the average queue depth is at the maximum threshold. Reference: Introduction to IP QoS p.5-9
QUESTION 147
What are two features that allow AutoQos to recognize voice traffic? (choose two)
A. a new QoS tag unique to phones
B. trust boundaries to allow the switch to track IP phones on the network
C. CallManager device table queries
D. IP phone registration with each AutoQoS server
E. automatic configuartion of an MQC class for voice signalling traffic
Correct Answer: BE Section: (none) Explanation
Explanation/Reference:
Page 2,12, Cisco AutoQoS White Paper,
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