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2013 Latest Cisco 350-001 Exam Section 2: Congestion Management (9 Questions)

QUESTION NO: 1
The following are 3 separate queues for a router configured to prioritize traffic: Queue 2 is a low-latency queue running in alternate-priority mode. The interface MTU is 1500. The queue weights are as follows:
Weight of 1 for Queue 2 Weight of 2 for Queue 1 Weight of 1 for Queue 0
Assume that all the default counters are currently zero (0) and Queue 2 will be serviced first, how many packets will be left in Queue 2 after both of the other queues have been serviced once?
A. 0
B. 1
C. 3
D. 500
E. 1500
Answer: B
Explanation:
Since the example states that Q2 is serviced alternately with Q1 and Q0, the order goes Q2, Q1, Q2, Q0, Q2, etc. The quantum values calculated as MTU + (weight-1)*512 per queue are: Q2 = 1500, Q1= 2012 (MTU + (weight-1)*512) & Q0 = 1500. Therefore immediately after Q0 is serviced there is still a single packet in Q2.
Further clarification (step by step):
MTU is 1500.
Weight of1 for Queue 0 => 1500 bytes will be de-queued in first round
Weight of2 for Queue 1 =>1500 +(2-1)*512 =2012 bytes will be de-queued per round
Weight of1 for Queue 2=> 1500 bytes will be de-queued in first round
Sequence of de queuing operation…
Q2 first (500 byte) and second (1500 byte) packet offloaded. Deficit 1500-2000= –500
Q1 first (500 byte) second (1500 byte) third (500 byte packet offloadedDeficit2012-2500=-488
Q2 1500 -500 = 1000 bytes can be off loaded third (500 byte) and fourth (500 byte) packet are removed.

last packet 1500 byte still remains.
Q0 First (1500 byte) packet is off loaded.
Q 2 Is being served after both the other queues have had their initial pass.
How many packets remain in Q 2 after first runis what the question is asking.
The answer is 1.

QUESTION NO: 2
Which of the following is FALSE regarding differences between Generic Traffic Shaping (GTS) and Frame Relay Traffic Shaping (FRTS)?
A. GTS supports the traffic group command while FRTS does not.
B. For GTS, the shaping queue is weighted fair queue (WFQ). FRTS does not support WFQ. With FRTS, the queue can be a CQ, PQ or FIFO.
C. FRTS supports shaping on a per-DLCI basis, while GTS is configurable per interface or subinterface.
D. GTS works with a variety of Layer 2 technologies, including Frame Relay, ATM, Switched Multimegabit Data Service, and Ethernet. FRTS is supported only on Frame Relay interfaces.
Answer: B
Explanation:
B. For FRTS, the queue can indeed be a weighted fair queue (configured by the frame-relay fair-queue command), a strict priority queue with WFQ (configured by the frame-relay ip rtp priority command in addition to the frame-relay fair-queue command), custom queuing (CQ), priority queuing (PQ), or first-in, first-out (FIFO). Differences Between Traffic-Shaping Mechanisms Generic traffic shaping (GTS), class-based shaping, distributed traffic shaping (DTS), and Frame Relay traffic shaping (FRTS) are similar in implementation, share the same code and data structures, but differ in regard to their CLIs and queue types used. Following are some examples in which these mechanisms differ:
1.
For GTS, the shaping queue is a weighted fair queue. For FRTS, the queue can be a
weighted fair queue (configured by the frame-relay fair-queue command), a strict priority
queue with WFQ (configured by the frame-relay ip rtp priority command in addition to
the frame-relay fair-queue command), custom queuing (CQ), priority queuing (PQ), or
first-in, first-out (FIFO).

2.
For class-based shaping, GTS can be configured on a class, rather than only on an access control list (ACL). To do so, you must first define traffic classes based on match criteria including protocols, access control lists (ACLs), and input interfaces. Traffic shaping can be applied to each defined class.
3.
subinterface.
Incorrect Answers:
A, C, D. These statements are all true. For more on FRTS and GTS see the following
URL (towards the bottom):
Reference:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800bd8e

QUESTION NO: 3 The TestKing router shown in the following exhibit has a frame relay link with a port speed of 256K and a PVC CIR speed of 64K. The Testking router is receiving a notification form the Frame Relay provider that there is congestion in the network.
You want the router to react dynamically to this notification from the Frame relay provider.
What command should you issue to do this?
A. traffic-shape adaptive 64000
B. fair-queue 64000
C. shape peak 256000 64000
D. frame-relay class Testking
Answer: A
When the provider is sending messages to the frame relay customer that there is congestion notifications, they send Backward Explicit Congestion Notification messages (BECNs). As you can see from the definition below, the traffic shape adaptive command enables the router to react to this:
traffic-shape adaptive [bit-rate] configures minimum bit rate to which traffic is shaped when backward explicit congestion notifications (BECNs) are received on an interface.
With adaptive GTS, the router uses backward explicit congestion notifications (BECNs) to estimate the available bandwidth and adjust the transmission rate accordingly. The actual maximum transmission rate will be between the rate specified in the traffic-shape adaptive command and the rate specified in the traffic-shape rate command.
As you can see this fulfills the requirement of the question about the Frame Relay network sending information about congestion.
Incorrect Answers:
B, C. These commands will not enable the router to dynamically react to the BECN messages.
D. The Frame-relay class is command is setting up a map class. When a map class is applied to the main interface all the VC gets the traffic shaping from the main interface. This command needs too much assuming while the traffic-rate command does not.

QUESTION NO: 4 In the Testking Frame Relay network, Class Based Shaping is being used to increase network performance. Which of the following is a true statement regarding Class Based Shaping?
A. CB shaping allows to rate-limit traffic in both incoming and outgoing directions.
B. CB shaping provides a rate-limiting functionality with an associated amount of buffers, to store temporary out of profile traffic.
C. CB shaping can only be configured in a child policy in a hierarchical policy map.
D. CB shaping is a versatile feature which allows to both queue and remark traffic in input.
E. None of the above
F. All of the above
Answer: B
Explanation:
Traffic shaping allows you to control the traffic going out an interface in order to match its transmission to the speed of the remote, target interface and to ensure that the traffic conforms to policies contracted for it. Traffic adhering to a particular profile can be shaped to meet downstream requirements, thereby eliminating bottlenecks in topologies with data-rate mismatches. This is done with the use of buffers, which are used to temporarily store traffic that is queued. An optional Class Based Shaping command allows for the maximum number of buffers to be adjusted.
Incorrect Answers:
A, D. Class Based Shaping is used for rate limiting outgoing traffic only. It does not provide for any mechanism to shape of mark incoming traffic.
C. Class Based Shaping uses class-map statements. A set of hierarchical policy maps are not required for configuring CBS.

QUESTION NO: 5
The Testking network is using FRTS to optimize the data flows within the network.
In frame-relay traffic shaping (FRTS), what is the Committed burst (Bc)
parameter?

A. The Bc is optional, and can be 0. It tells IOS how much extra bandwidth can be used on top of the CIR.
B. The Bc is a parameter which needs to be negotiated with the provider of the frame-relay circuit. It defines the percentage of the frame-relay circuit IOS will use to send bursty traffic.
C. Bc is a mandatory parameter when configuring FRTS. It defines a traffic rate up to which IOS will send traffic.
D. Bc defines the amount of token added to the token bucket at each interval. The token bucket algorithm is used in FRTS. If not configured, it defaults to 56000 bits.
E. Bc is total size of the token bucket. This includes the excess burst and conform burst.
F. None of the above are true.
Answer: A
Explanation:
Bc (Committed Burst) is defined as the Maximum number of bits the frame relay network commits to transfer over a Committed Rate Measurement Interval (Tc). Tc = Bc / CIR. It is an optional parameter that defaults to 7000 bits, but it can indeed be set to 0, which means that no traffic will be able to burst above the CIR.
Incorrect Answers:
B. The Bc is a value specified in bits per interval, not in a percentage.
C. Bc is optional, not mandatory. The only mandatory configuration guidelines for FRTS is to specify the interface with frame-relay encapsulation, and to enable FRTS with the “frame-relay traffic-shaping” interface command.
D. The default committed burst size is 7000 bits, when no value is specified. The default Bc value for priority queuing on frame relay links is 56000, but it is 7000 for regular FRTS.
E. Bc is the committed burst rate, not the total burst.

QUESTION NO 6:
In weighted fair queuing (WFQ), one can configure a ‘congestive-discard-threshold’
(CDT). What is the CDT value used for?

A. This threshold specifies from which point on IOS should start using WFQ.
B. The CDT specifies the number of messages allowed in each queue.
C. The CDT specifies the maximum amount of messages to be used by WFQ for high bandwidth traffic, dropping packets from the most aggressive flow.
D. The CDT defines a value from when IOS starts to account all messages in the WFQ system in conjunction with Netflow.
E. CDT refers to the maximum amount of dynamic flows IOS will allow for WFQ.
F. None of the above
Answer: C
Explanation:
WFQ provides traffic priority management that automatically sorts among individual traffic streams without requiring that you first define access lists. WFQ can also manage duplex data streams such as those between pairs of applications, and simplex data streams such as voice or video. There are two categories of WFQ sessions: high bandwidth and low bandwidth. Low-bandwidth traffic has effective priority over high-bandwidth traffic, and high-bandwidth traffic shares the transmission service proportionally according to assigned weights. Example: The following example requests a fair queue with a congestive discard threshold of 64 messages, 512—dynamic queues, and 18 RSVP queues:
interface Serial 3/0
ip unnumbered Ethernet 0/0
fair-queue 64 512 18
When WFQ is enabled for an interface, new messages for high-bandwidth traffic streams are discarded after the configured or default congestive messages threshold has been met. However, low-bandwidthconversations, which include control message conversations, continue to enqueue data. As a result, the fair queue may occasionally contain more messages than its configured threshold number specifies.

QUESTION NO: 7
What is true about Class based Weighted Fair Queuing (CBWFQ)?

A. CBWFQ provides delay, jitter and bandwidth guarantees to traffic.
B. CBWFQ can be configured on any interface in either input or output.
C. CBWFQ has to be configured with the Modular QoS CLI. The resulting service-policy has to be applied on output.
D. CBWFQ can only be configured in a hierarchical policy-map. The parent policy-map does policing and the child policy-map does CBWFQ.
E. All of the above
F. None of the above
Answer: C
Explanation:
To configure CBWFQ, there are 3 required steps: Defining class maps, configuring class policy in the policy map, and attaching the service policy and enabling CBWFQ. This is done using the new IOS syntax called Modular QoS. You must use the Modular QoS CLI to configure class based marking.
Incorrect Answers:
A. There is no way to specify traffic guarantees for jitter and delay, as the underlying network that is used for transport will have the greatest impact on these values.
B. The CBWFQ service policy can only be applied to outbound interfaces.
D. Although CBWFQ is typically configured using this method, it not not required for all implementations. Reference: Distributed QoS, Odom/Cavanaugh, Cisco Press, page 176.

QUESTION NO: 8 CAR has been configured on router TK1. What best defined Committed Access Rate (CAR)?
A. CAR allows metering of traffic for traffic shaping.
B. CAR is a feature that allows the rate limiting of traffic in either the incoming or outgoing direction.
C. CAR is part of a set of features to be used in conjunction with queuing to form a hierarchical policy. CAR must always be applied in a parent policy-map, whereas CBWFQ should be applied in a child policy-map.
D. CAR is a queuing feature.
E. CAR matches only on UDP port range {16384 – 32767}.
Answer: B

Explanation:
The Committed Access Rate (CAR) and Distributed CAR (DCAR) services limit the input or output transmission rate on an interface or subinterface based on a flexible set of criteria. The rate-limiting feature of CAR provides the network operator with the means to define Layer 3 aggregate or granular access, or egress bandwidth rate limits, and to specify traffic handling policies when the traffic either conforms to or exceeds the specified rate limits. Aggregate access or egress matches all packets on an interface or subinterface. Granular access or egress matches a particular type of traffic based on precedence. You can designate CAR rate-limiting policies based on physical port, packet classification, IP address, MAC address, application flow, and other criteria specifiable by access lists or extended access lists. CAR rate limits may be implemented either on input or output interfaces or subinterfaces including Frame Relay and ATM subinterfaces. An example of use of CAR’s rate-limiting capability is application-based rates limiting HTTP World Wide Web traffic to 50 percent of link bandwidth, which ensures capacity for non-Web traffic including mission-critical applications.

QUESTION NO: 9 QoS mechanisms have been put in place within the TestKing network using IP precedence. This IP precedence can be defined as:
A. The ToS byte is the IP precedence
B. The middle 4 bits of the ToS byte
C. The 3 left most bits of the ToS byte
D. The 3 right most bits of the ToS byte
E. The right most bit of the ToS byte
Answer: C
Explanation:
Within the Type of Service (TOS) byte, the three most significant bits are the IP precedence bits. The TOS byte is displayed below:
ToS Byte
P2 P1 P0 T2 T1 T0 CU1 CU0
IP precedence-three bits (P2 to P0)
2.
Delay, Throughput and Reliability-three bits (T2 to T0)
3.
CU (Currently Unused)-two bits(CU1-CU0)
Reference: http://www.cisco.com/warp/public/105/dscpvalues.html Leading the way in IT testing and certification tools, www.testking.com
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