642-785 Maintaining Cisco Service Provider Quality of Service

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Question 1

Refer to the exhibit.

Which two statements are correct? (Choose two.)

  • A. The policy map cust-policy specifies an average traffic shaping rate of 384 kb/s for the cust1 class and assigns the service policy cust1-classes to the cust1 class.
  • B. This example is a hierarchical MQC example, and the cust-policy is the child policy.
  • C. This example queues the traffic into different CBWFQ classes before the aggregate traffic is shaped.
  • D. Within the cust1-classes policy, the gold class is guaranteed 50 percent of the bandwidth. Silver is guaranteed 20 percent of the bandwidth, and bronze is guaranteed 15 percent of the bandwidth.
  • E. The traffic class cust2 is ensured a bandwidth of 51.2 kb/s.
  • F. Within the cust2-classes policy, the gold class is guaranteed 30 percent of the S3/2 interface bandwidth. Silver is guaranteed 15 percent of the S3/2 interface bandwidth. Bronze is guaranteed 10 percent of the S3/2 interface bandwidth.

Answer : A,D

Question 2

Which two statements about IP SLA are correct? (Choose two.)

  • A. Cisco IOS IP SLA is Layer 2 transport independent.
  • B. IOS IP SLA uses active traffic monitoring which allows users to analyze service levels for IP applications.
  • C. IOS IP SLA is a traffic monitoring mechanism that gathers statistics about traffic based on packet headers and fields.
  • D. Cisco IOS IP SLA can be used to help detail billing information for each defined class of service.
  • E. IP SLA uses NBAR to provide the reporting engine for statistics that it collects.

Answer : A,B

Question 3

When the customer LAN is managed by the service provider and the network is
oversubscribed, what is the best location for use of congestion avoidance mechanisms?

  • A. on output interfaces from the customer LAN leading into the service provider network
  • B. in interfaces in the service provider network incoming from the customer LAN
  • C. in the service provider core
  • D. on output interfaces from the service provider network leading to the customer LAN

Answer : A

Question 4

When troubleshooting a QoS problem, which two key statistics should you look for?
(Choose two.)

  • A. queue utilization
  • B. interface utilization
  • C. queue priority
  • D. queue drops
  • E. queue depth

Answer : D,E

Question 5

The provider you work for supports a wide range of Cisco router models and Cisco IOS
Software releases. You are in the process of moving to a SNMP-based tool to monitor QoS
configurations and statistics. What are some of the challenges to this approach?

  • A. The SNMP MIB provides direct access into the QoS configuration parameters. Poor configuration could lead to changes that are difficult to track.
  • B. Some models of Cisco routers do not have full support for the class-based QoS MIB, which results in a number of elements that cannot be managed.
  • C. Older versions of Cisco IOS Software do not maintain index persistency, which results in significant changes in the information that is collected unless properly configured.
  • D. SNMP should be used in conjunction only with Cisco IP SLA to ensure that the information gathered is reported properly.

Answer : C

Question 6

Refer to the exhibit.

You have implemented RFC 3270 Pipe mode in your MPLS network. A customer packet
with the DSCP value of AF31 has been sent to the ingress PE router. The PE router has
set the MPLS experimental bits per policy, but the policer has remarked the experimental
bits of the top label. What will the DSCP value of the packet be when it leaves the egress
PE router?

  • A. BE
  • B. CS1
  • C. CS3
  • D. CS4
  • E. AF31

Answer : E

Question 7

What can be used to provide read-only access to QoS configuration information and
statistics from a network management station?

  • A. NetFlow
  • D. NBAR
  • E. IP SLA

Answer : B

Question 8

Refer to the exhibit.

A customer's policy profile was updated to increase the minimum bandwidth to 256 kb/s for
mission critical data, but reports indicate that the policy now has an error. What change
should be made to the policy to correct this error?

  • A. The bandwidth statement should read 256000.
  • B. Set the shape rate to a CIR that is higher than 256 kb/s.
  • C. Use the shape peak command instead of the shape average command.
  • D. Increase the maximum queue size to 128 to compensate for the mission critical data.
  • E. The priority command should have been used, not the bandwidth command.

Answer : B

Question 9

Refer to the exhibit.

A service provider moved from a three-class service provider QoS model to a four-class
service provider QoS model. A new class of service called CRITICAL-B was created to
support traffic with a DSCP marking of AF31. A customer reports that the traffic in the
CRITICAL-B class is having problems. What step should the service provider take to
correct this issue?

  • A. The class map for CRITICAL-B should have a DSCP value of 28.
  • B. The max-reserved-bandwidth command must be used to allocate more bandwidth than allowed by default.
  • C. The policy map should be updated to move the BULK class to the bottom of the policy.
  • D. The CRITICAL-A class should change from match-all to match-any.

Answer : C

Question 10

When the RFC 3270 Pipe mode is used, the PHB at the egress router is based on which of

  • A. The topmost MPLS label EXP value.
  • B. The MPLS VPN label EXP value.
  • C. The Differentiated Services field value in the IP packet header.
  • D. The packet is re-evaluated, remarked, and the PHB is based on this new marking.

Answer : A

Question 11

Refer to the exhibit.

Which two statements about the SP-REALTIME traffic class are true? (Choose two.)

  • A. Traffic is queued using LLQ.
  • B. Traffic is policed to 35 percent of the interface bandwidth.
  • C. The priority configuration command is missing the maximum guaranteed bandwidth rate.
  • D. The police configuration command is missing the violate-action option.
  • E. Traffic conforming to the police rate will be transmitted and all the markings on the packets will be cleared.

Answer : A,B

Question 12

You have deployed IP SLA in your network to monitor VoIP. You want to be notified on
network delay before it affects voice quality. What threshold should be set?

  • A. 150 ms one-way
  • B. 150 ms round trip
  • C. 50 ms round trip
  • D. 250 ms one-way
  • E. 200 ms round trip

Answer : A

Question 13

A service provider recently changed from RFC 3270 Uniform mode to Pipe mode. Which
three considerations about this change are true? (Choose three.)

  • A. If the provider moved to a Short Pipe mode model, it would allow them to implement customer-specific QoS policy on the PE egress.
  • B. The Pipe mode provides the isolation between the customer and provider DiffServ domains, while maintaining a simpler support model.
  • C. The Short Pipe mode derives the outbound classification of the WRED and WFQ based on the DiffServ policy of the provider.
  • D. In Uniform mode, when the topmost EXP value is changed, the changed EXP value will propagate to the original IP precedence or DSCP.

Answer : A,B,D

Question 14

Which statement about the MQC configuration shown here for the class-default traffic class
is true?
policy-map CE-EDGE-4CLASS-OC3-POS-1
class class-default
bandwidth percent 25

  • A. The maximum number of packets the queue for the class-default class can hold is 64 packets using the default queue-limit.
  • B. The bandwidth percent is referenced to the reserved bandwidth on the interface.
  • C. This configuration is invalid, because the class-default traffic class does not support the bandwidth command.
  • D. The class-default class will use WFQ instead of FIFO queueing.

Answer : A

Question 15

Refer to the exhibit.

Which statement is correct?

  • A. This policy map is applied to the FastEthernet0/0 interface in the input direction.
  • B. No traffic matched the SP-REALTIME class.
  • C. A total of 133836 packets have been transmitted out of the FastEthernet0/0 interface.
  • D. Packets marked with both DSCP EF and MPLS EXP 5 markings will not be classified into the SP-REALTIME traffic class.
  • E. The FastEthernet0/0 interface is using CBWFQ egress queueing.

Answer : C

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