Maintaining Cisco Service Provider Quality of … · Maintaining Cisco Service Provider Quality of ... is easy to design and ... 6/qos/configuration/guide/qc36over.pdf QUESTION 26

Cisco.Actualtests.642.785.v2012-9-17.byDD.91q

Number: 642-785Passing Score: 800Time Limit: 120 minFile Version: 1.0

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Maintaining Cisco Service Provider Quality of Servi ce Version: 5.1

91 questions version June 22,2012

I did not yet sanitize all the answers or compare against any other dumps - DD 9-17--2012

Exam A

QUESTION 1Within a QoS policy-map configuration, one of the traffic classes is configured with the random detectdscp-based configuration command. What will that command accomplish?

A. provides congestion management by queueing the traffic using CBWFQB. provides congestion management by queueing the traffic using LLQC. decreases the probability of congestion by selectively dropping TCP packets before the queue

is fullD. provides congestion avoidance by selectively delaying the delivery of packets with lower DSCP

prioritE. decreases congestion by avoiding global UDP synchronization

Correct Answer: CSection: (none)Explanation

Explanation/Reference:

QUESTION 2What are three benefits of IntServ and RSVP? (Choose three.)

A. RSVP helps network devices identify dynamic port numbers.B. IntServ networks will reject or downgrade new RSVP sessions if all reservable bandwidth is

booked somewhere in a path.C. RSVP signaling is a scalable way to ensure all devices maintain an accurate picture of the

network state.D. They enable the network to guarantee necessary QoS to individual data flows.E. The IntServ class-based approach is easy to design and implement.

Correct Answer: ABDSection: (none)Explanation


QUESTION 3Which statement about the rates and statistics (such as match, transmit, drop, and police) shownin the show policy-map interface output is true?

A. The rates are computed as a moving average of instantaneous rates.B. The rates are displayed in real time, which matches the actual traffic rate.C. The matched statistics of the packet can be cleared only when the router rebootsD. The matched statistics of the packet are displayed in real time.E. The traffic policing statistics are displayed in real time.

Correct Answer: ASection: (none)Explanation


QUESTION 4Which four factors can be used for packet classification in a QoS-aware network device? (Choosefour.)

A. source addressB. destination addressC. DSCPD. TTLE. MQCF. IP precedence

Correct Answer: ABCFSection: (none)Explanation


QUESTION 5What are the three primary types of faults associated with QoS fault management? (Choosethree.)


A. classification faultsB. buffer faultsC. queue faultsD. marking faultsE. assurance faultsF. physical faults

Correct Answer: ADESection: (none)Explanation


QUESTION 6Which are the two locations where the SP network device always trusts the QoS markings from itsupstream neighbor? (Choose two.)

A. at the ingress PEB. at the egress PEC. in the SP coreD. at the ingress CEE. at the egress CE

Correct Answer: BCSection: (none)Explanation


QUESTION 7Which of these correctly describes traffic classification using qos-group?

A. qos-group marking is automatically mapped to MPLS EXP marking.B. qos-group is only applicable to an MPLS-enabled router.C. qos-group marking value ranges from 0 to 7.D. qos-group is local to the router.

Correct Answer: DSection: (none)Explanation

Explanation/Reference:https://supportforums.cisco.com/thread/190450

QUESTION 8Which two IP SLA Probe types can be used to measure voice quality? (Choose two.)

A. HTTPB. ICMP Path JitterC. UDP EchoD. UDP JitterE. UDP DelayF. UDP MOS

Correct Answer: BDSection: (none)Explanation


QUESTION 9Refer to the exhibit.

Traffic in CLASS-B is not getting a minimum bandwidth of 192 kb/s in this policy map. What canbe done to correct this?

A. No changes are needed, the site is already correct.B. The shape peak command should be used instead of the shape average command.C. Set the shape rate to a CIR higher than 192 kb/s.

D. Decrease the maximum queue size.



QUESTION 10Which of these describes Short Pipe mode in QoS for MPLS VPN service providers?

A. Service provider can remark customer DSCP values.B. Service provider does not remark customer DSCP values. (Service provider uses independent

MPLS EXP markings.) Final PE-to-CE policies are based on service provider markings.C. The customer and service provider share the same DiffServ domain.D. Service provider does not remark customer DSCP values. (Service provider uses independent

MPLS EXP markings.) Final PE-to-CE policies are based on customer markings.


Explanation/Reference:http://www.cisco.com/en/US/tech/tk436/tk428/technologies_tech_note09186a008022ad7e.shtml#shortpipe


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 cust1class 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 guaranteed10 percent of the S3/2 interface bandwidth.

Correct Answer: ADSection: (none)Explanation



A customer's policy profile was updated to increase the minimum bandwidth to 256 kb/s formission critical data, but reports indicate that the policy now has an error. What change should bemade 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.

Correct Answer: BSection: (none)Explanation


QUESTION 13Which 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.

Correct Answer: ABSection: (none)Explanation


QUESTION 14You have deployed IP SLA in your network to monitor VoIP. You want to be notified on networkdelay before it affects voice quality. What threshold should be set?

A. 150 ms one-wayB. 150 ms round tripC. 50 ms round tripD. 250 ms one-way

E. 200 ms round trip



QUESTION 15When troubleshooting a QoS problem, which two key statistics should you look for? (Choose two.)

A. queue utilizationB. interface utilizationC. queue priorityD. queue dropsE. queue depth

Correct Answer: DESection: (none)Explanation


QUESTION 16Which three NetFlow versions are supported by Cisco NetFlow Analyzer? (Choose three.)

A. 1B. 5C. 6D. 7E. 8F. 9

Correct Answer: ABFSection: (none)Explanation


QUESTION 17Which command shows real traffic statistics on each class map on the 10 Gigabit interface0/10/0/0 at the egress direction?

A. show service-policy interface tenGigE 0/10/0/0 outputB. show service-policy interface tenGigE 0/10/0/0 egressC. show policy-map interface tenGigE 0/10/0/0 outputD. show policy-map interface tenGigE 0/10/0/0 egressE. show qos interface tenGigE 0/10/0/0 outputF. show qos interface tenGigE 0/10/0/0 egress

Correct Answer: C

Section: (none)Explanation

Explanation/Reference:http://www.cisco.com/en/US/tech/tk543/tk760/technologies_tech_note09186a0080108e2d.shtml

QUESTION 18When is a best-effort QoS policy most appropriate?

A. when the customer has high bandwidth access to the networkB. when the customer will only transport delay-tolerant dataC. when the CE is self-managed and the customer provides adequate QoS markingD. when the customer plans to transport data from no more than one multimedia application



QUESTION 19Which Cisco IOS command will show a summary of probes?

A. show ip sla statisticsB. show ip sla responderC. show ip sla monitorsD. show ip sla monitors



QUESTION 20Where do service providers apply policy when traffic is leaving the customer network? (Choosetwo.)

A. Apply input policy on the CE interface toward PE, if CE is unmanaged.B. Apply input policy on the PE interface toward CE, if CE is unmanaged.C. Apply input policy on the PE interface toward CE, if CE is managed.D. Apply output policy on the PE interface toward CE, if CE is managed.E. Apply output policy on the CE interface toward PE, if CE is managed.

Correct Answer: BESection: (none)Explanation


QUESTION 21Which two methods can be used to monitor QoS performance? (Choose two.)

A. SNMPB. SYSLOGC. TFTPD. RMONE. NetFlow

Correct Answer: AESection: (none)Explanation

Explanation/Reference:https://supportforums.cisco.com/thread/2051010

Netflow is based on RMON/RMON2


Voice quality is poor on calls placed between the two sites. What change would you recommendto solve this problem?

A. Set up WRED to help avoid link congestion.B. Increase the bandwidth of the voice priority queue.C. Change the voice class map to match DSCP EF or CS5.D. Lower the total bandwidth allocated for the video, critical, and class-default queues, because

they are starving the voice queue.



QUESTION 23Which two items can be obtained from the CISCO-NETFLOW-MIB? (Choose two.)

A. buffer hitsB. CEF tablesC. signal-to-noise ratioD. cache configurationE. protocol statistics

Correct Answer: DESection: (none)Explanation

Explanation/Reference:http://www.cisco.com/en/US/docs/ios/12_3t/12_3t7/feature/guide/nflowmib.html

QUESTION 24Where would you apply WRED to avoid congestion and poor QoS from oversubscription of thenetwork?

A. wherever there is a potential bottleneckB. wherever there is a potential bottleneck and most traffic is TCPC. wherever there is a potential bottleneck and traffic is delay-intolerantD. wherever there is a potential bottleneck and most traffic is UDPE. wherever there is a potential bottleneck and most traffic is voice



QUESTION 25Which MQC capabilities are unique to Cisco IOS XR Software?

A. classification and markingB. congestion management

C. congestion avoidanceD. policing and shapingE. fabric qos

Correct Answer: ESection: (none)Explanation

Explanation/Reference:http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.6/qos/configuration/guide/qc36over.pdf

QUESTION 26An MPLS VPN customer reports that their DSCP markings from one CE to another CE are beingremarked by the service provider. What can cause customer packets to be remarked?

A. The MPLS VPN service provider is using Penultimate Hop Popping.B. The service provider is using Uniform mode as the MPLS QoS tunnel mode.C. The service provider is using the Short Pipe mode as the MPLS QoS tunnel mode.D. The service provider is using Pipe mode as the MPLS QoS tunnel mode.


Explanation/Reference:http://www.cisco.com/en/US/tech/tk436/tk428/technologies_tech_note09186a008022ad7e.shtml

QUESTION 27A customer reports that the packets from their custom TCP application, which is currently markedas DSCP AF43, is being dropped more frequently than desired. All of the links in service providernetwork are using DSCP-based WRED. What can be changed to best improve the drop rate of thecustomer's custom application without causing major problems for the other traffic classes?

A. Remove WRED on all the links.B. Mark the custom application traffic to DSCP EF instead.C. Mark the custom application traffic to DSCP AF41 instead.D. Use a different queuing method for the AF43 traffic class.E. Allocate more bandwidth to the AF43 traffic class.


Explanation/Reference:http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800949f2.shtml#dscpcompliantwred

DSCP-Compliant WRED Weighted Random Early Detection (WRED), selectively discards lower-priority traffic when the interface beginsto get congested. WRED can provide differentiated performance characteristics for different CoS.

QUESTION 28Which Cisco IOS XR command will help troubleshoot why a policy map fails to apply on aninterface?

A. show service-policy interface tenGigE 0/0/0/0B. show service-policy interface tenGigE 0/0/0/0C. show policy mgr qos trace allD. show qos interface tenGigE 0/0/0/0E. show qos interface tenGigE 0/0/0/0


Explanation/Reference:original answer was C show policy mgr qos trace all

I could not find that one command for any Cisco IOS but there is:

show qos ea traceTo display the processing information of the QoS component on the line card, use the show qos ea tracecommand in EXEC mode.show qos ea trace [all] [file name original location node-id] [hexdump] [last entries] [location node-id][tailf] [misc] [reverse] [stats] [unique] [verbose] [wrapping] [internal] [external] [errors] [qfifo]

and

show policy-map targetsTo display information about the interfaces on which policy maps are applied, use the show policy-maptargets command in EXEC mode.show policy-map targets [location node-id| pmap-name name| type performance-traffic [location node-id|

pmap-name name]| type qos [location node-id| pmap-name name]]

http://www.cisco.com/en/US/docs/routers/crs/software/crs_r4.0/qos/command/reference/b_qr40crs.pdf

QUESTION 29Which Cisco IOS command lists all traffic classifications?

A. show class-mapB. show policy-mapC. show service-policyD. show qos




Your MPLS network is using RFC 3270 Uniform mode. Your customer reports that when aMicrosoft NetMeeting call is placed between the workstations, the user at 172.16.1.2 experiencesacceptable audio quality but the user at 172.16.2.2 experiences poor audio quality. What course ofaction should you take?

A. Change your policy to not remark audio packets within your network.B. Have the customer set the correct marking of audio packets at the 172.16.1.2 device.C. Have the customer set the correct marking of audio packets at the 172.16.2.2 device.D. Use a policy map at the ingress to the PE1 router to remark packets from 172.16.1.2.E. Use a policy map at the ingress to the PE2 router to remark packets from 172.16.2.2.



QUESTION 31

Which two tools can be used to monitor and report on if a QoS queue is working on a networkdevice? (Choose two.)

A. CiscoWorks IPMB. RemedyC. InfoVistaD. NetCoolE. IP SLAF. Splunk

Correct Answer: ACSection: (none)Explanation


QUESTION 32What are the benefits of using differentiated services in the service provider backbone? (Choosetwo.)

A. simple, easy to design, deploy, and operateB. less bandwidth required to achieve the same SLAC. more aggregate traffic supportedD. overprovision by two times the maximum aggregate

Correct Answer: BCSection: (none)Explanation


QUESTION 33Which statement about the MQC configuration shown here for the class-default traffic class istrue?

policy-map CE-EDGE-4CLASS-OC3-POS-1class class-defaultbandwidth percent 25!

A. The maximum number of packets the queue for the class-default class can hold is 64 packetsusing the default queue-limit.

B. The bandwidth percent is referenced to the reserved bandwidth on the interface.C. The bandwidth percent is referenced to the reserved bandwidth on the interface.D. The class-default class will use WFQ instead of FIFO queueing.



QUESTION 34A customer reports drops for traffic in the BIZ-CRITICAL class. As part of the verification processyou identify that there is a high number of random drops. Which of these can help address thisproblem?

A. Decrease the queue limit for the traffic class.B. Increase the WRED min threshold value for the traffic class.C. Enable fair queuing for the BIZ-CRITICAL class.D. Decrease the WRED drop probability denominator for the class.


Explanation/Reference:http://www.cisco.com/en/US/docs/ios/11_2/feature/guide/wred_gs.html

QUESTION 35What three statements about WRED are true? (Choose three.)

A. WRED is a congestion avoidance technique.B. Using WRED on the edge devices (CE, PE) is an effective method of implementing congestion

avoidance in the service provider network, because it avoids the congestion prior to reaching thecore.

C. WRED should always be used in traffic classes that support a MIX of realtime UDP and TCPtraffic.

D. WRED employs a weighted method for determining which packets to drop to avoid congestion.Packets with a higher precedence are less likely to be dropped

E. Using WRED will necessitate a large number of dropped packets



QUESTION 36An MPLS VPN customer with managed CE services recently made some changes to their call managerconfigurations. Now the customer reports that their VoIP traffic voice quality is very poor.What could be a cause of the problem?

A. The VoIP traffic class is not being policed at the CE router egressB. The VoIP traffic is being marked as DSCP EF.C. The customer changed the codec used for voice compression from G.729 to G.711.D. RTP header compression is used for the VoIP traffic class.E. manager configurations. Now the customer reports that their VoIP traffic voice quality is very poor.

What could be a cause of the problem?



QUESTION 37A MPLS VPN customer reports poor VoIP call quality across the MPLS VPN. What could be theproblem?

A. All the core links in the service provider network are using LLQ.B. The service provider is using RTP header compression on the high-speed core links.C. The total end-to-end delay measured is constantly over 350 msec.D. The service provider is using the Short Pipe mode rather than the Uniform mode.E. The service provider has assigned more than 33% of the interface bandwidth to the priority

class.




Some customers report that at peak times during the day their average throughput seems to beless than what they expect. While troubleshooting, you notice that data flows sometimes seem tobe synchronized with a tendency to increase then drop off in a repeating manner. Which actionwould help to alleviate this situation?

A. Implement traffic shaping to smooth out the peaks and troughs.B. Implement WRED to help prevent tail drops during periods of congestion.C. Change your QoS model from DiffServ to IntServ for better QoS scalability.D. Decrease the size of output queues in the network to allow the scheduler to allocate link

bandwidth fairly.




You have implemented RFC 3270 Uniform mode in your MPLS network. A customer packet withthe DSCP value of AF31 has been sent to the ingress PE router. The PE router has mapped theDSCP values into the MPLS experimental bits, but the policer has remarked the experimental bitsof the top label. What will the DSCP value of the packet be when it leaves the egress PE router?

A. BEB. CS1C. CS3D. AF31


Explanation/Reference:MPLS Experimental Field

Setting the MPLS experimental (EXP) field value satisfies the requirement of service providers who do not wantthe value of the IP precedence field modified within IP packets transported through their networks.

By choosing different values for the MPLS EXP field, you can mark packets so that packets have the prioritythat they require during periods of congestion.

By default, the IP precedence value is copied into the MPLS EXP field during imposition.You can mark theMPLS EXP bits with an MPLS QoS policy.

DSCP CS1 is mapped into EXP 1

QUESTION 40Which Cisco IOS XR Software command clears the service-policy counters on the 10 Gigabitinterface 0/0/0/0 at the ingress direction?

A. clear qos counters tenGigE 0/0/0/0 inputB. clear service-policy counters tenGigE 0/0/0/0 inputC. clear service-policy counters tenGigE 0/0/0/0 ingressD. clear service-policy counters tenGigE 0/0/0/0 ingressE. clear counters qos tenGigE 0/0/0/0 inputF. clear counters service-policy tenGigE 0/0/0/0 input



QUESTION 41What problem could occur when applying this policy map on CE?

policy-map CE-SP-MODELclass VOIPpriorityclass BROADCAST-VIDEOpriorityclass SP-CRITICAL-DATAbandwidth percent 40random-detect exp 3 15000 packets 45000 packets class class-defaultrandom-detect exp 1 2500 packets 7500 packetsrandom-detect exp 0 1500 packets 10500 packets

A. All traffic is classified and treated properly, no issues occur.B. Only one priority queue is allowed per policyC. No bandwidth or policing is configured for voice and video traffic, and other traffic could be

impacted.D. Default class does not have bandwidth assigned.




A customer has commented that voice quality is not meeting expectations when calls cross yournetwork. This voice packet was captured from the egress link to the customer. This capture isrepresentative of the customer’s voice packets across your network and the queuing methodshown is representative of packet treatment across your network. How might the problem be corrected?

A. Increase the bandwidth for the voice class.B. Set up multiple priority queues to ensure low latency for voice packets.C. Ensure that voice packets are correctly marked when they traverse your network.D. Enable WRED in the CBWFQs to minimize the possibility of dropping voice packets.



QUESTION 43Which three can be monitored by IP SLA? (Choose three.)

A. itterB. packet lossC. buffer allocationD. network delayE. queue utilization




You have implemented RFC 3270 Pipe mode in your MPLS network. A customer packet with theDSCP value of AF31 has been sent to the ingress PE router. The PE router has set the MPLSexperimental 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. BEB. CS1C. CS1D. CS4E. AF31


Explanation/Reference:Pipe mode is just like Short-Pipe mode, except the PHB on the mpls2ip link is selectedbased on the removed EXP value rather than the recently-exposed DSCP value. Theunderlying DSCP in the packet is not touched, but the mpls2ip path does not consider theDSCP for queuing on the egress link.

QUESTION 45When the RFC 3270 Pipe mode is used, the PHB at the egress router is based on which of these?

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.


Explanation/Reference:Pipe mode is just like Short-Pipe mode, except the PHB on the mpls2ip link is selectedbased on the removed EXP value rather than the recently-exposed DSCP value. Theunderlying DSCP in the packet is not touched, but the mpls2ip path does not consider theDSCP for queuing on the egress link.

QUESTION 46Which is the preferred queuing method provided by Cisco IOS Software for a converged VoIPnetwork?

A. WFQB. CBWFQC. LLQD. FIFO



QUESTION 47Which Cisco IOS feature is used to enable the following class map configuration?

class-map match-all test-cmmatch protocol gnutella file-transfer "*"


A. NetFlowB. CBWFQC. NBARD. Flexible Packets MatchingE. CAR



QUESTION 48What can be used to provide read-only access to QoS configuration information and statistics from a networkmanagement station?

A. NetFlowB. CISCO-CLASS-BASED-QOS-MIBC. SYSLOGD. NBARE. IP SLA


Explanation/Reference:http://www.cisco.com/en/US/docs/ios/12_4t/12_4t4/ht_cbqos.html

Feature Overview of the QoS: CBQoS MIB Index Enhanc ements

The cbQosConfigIndex, cbQosObjectsIndex, and cbQosPolicyIndex are volatile because when a networkingdevice reboots, the index numbers may change. This happens because system rebooting can cause the orderof the Modular QoS CLI (MQC) configuration to differ from the actual configuration order, which is user-drivenand unpredictable. As a result, you must read the MIB frequently to extract statistical and configurationinformation. Therefore, once a reload has occurred, the MIB has to be repolled to reestablish the indexes to thedata stored in the CBQoS MIB.

Traditionally, MIB persistence is handled by Cisco IOS APIs, which save the index and key information toNVRAM. The data is then retrieved and repopulated after reloading. However, this approach does not work wellfor the current implementation of the cbQosObjectsIndex because of the large amount of information thatneeds to be saved.

An index encoding scheme based on configuration entries instead of operational sequence is beingimplemented to provide persistent indexes on router reload so that MIB information retains the same set ofobject values each time that a networking device reboots.

Benefits of the QoS: CBQoS MIB Index Enhancements

Provide a Method to Produce MIB Indexes

These enhancements provide a repeatable method for generating MIB indexes so that they do not changebetween reboots.

Reduce Complexity for Network Management Applications

The complexity of configuring and correlating statistics objects is reduced, making it easier for networkmanagement applications to gather accurate information.

Maintain Compatibility with Previous MIBs

You do not need to make any changes to your Network Management Station (NMS) software since this featureis an infrastructure improvement that is backward compatible with older MIBs.


A service provider moved from a three-class service provider QoS model to a four-class serviceprovider QoS model. A new class of service called CRITICAL-B was created to support traffic witha 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.



QUESTION 50The provider you work for supports a wide range of Cisco router models and Cisco IOS Softwarereleases. You are in the process of moving to a SNMP-based tool to monitor QoS configurationsand statistics. What are some of the challenges to this approach?

A. The SNMP MIB provides direct access into the QoS configuration parameters. Poorconfiguration 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, whichresults in a number of elements that cannot be managed.

C. Older versions of Cisco IOS Software do not maintain index persistency, which results insignificant 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 informationgathered is reported properly.


Explanation/Reference:Interface Index Persistence feature introduced in Cisco IOS Release 12.1(5)T. This enhancement allowsinterfaces to be identified with unique values which will remain constant even when a device is rebooted. Theseinterface identification values are used for network monitoring and management using Simple NetworkManagement Protocol (SNMP)

One of the identifiers most commonly used in SNMP-based network management applications is the interfaceindex (ifIndex) value. IfIndex is a unique identifying number associated with a physical or logical interface; as faras most software is concerned, the ifIndex is the "name" of the interface.

Although there is no requirement in the relevant RFCs that the correspondence between particular ifIndexvalues and their interfaces be maintained across reboots, applications such as device inventory, billing, andfault detection increasingly depend on the maintenance of this correspondence.

Cisco IOS Release 12.1(5)T adds support for an ifIndex value that can persist across reboots, allowing users toavoid the workarounds previously required for consistent interface identification.

It is currently possible to poll the router at regular intervals to correlate the interfaces to the ifIndex, but it is notpractical to poll this interface constantly. If this data is not correlated constantly, however, the data may bemade invalid because of a reboot or the insertion of a new card into the router in between polls. Therefore,ifIndex persistence is the only way to guarantee data integrity.

IfIndex persistence means that the mapping between the ifDescr object values and the ifIndex object values(generated from the IF-MIB) will be retained across reboots.

Benefits

Association of Interfaces with Traffic Targets for Network Management

The Interface Index Persistence feature allows for greater accuracy when collecting and processing networkmanagement data by uniquely identifying input and output interfaces for traffic flows and SNMP statistics.Relating each interface to a known entity (such as an ISP customer) allows network management data to bemore effectively utilized.

Accuracy for Mediation, Fault Detection, and Billing

Network data is increasingly being used worldwide for usage-based billing, network planning, policyenforcement, and trend analysis. The ifIndex information is used to identify input and output interfaces for trafficflows and SNMP statistics. Inability to reliably relate each interface to a known entity, such as a customer,invalidates the data.

Restrictions

The interface-specific ifIndex persistence command ([no] snmp ifindex persistence) cannot be used onsubinterfaces. A command applied to an interface is automatically applied to all the subinterfaces associatedwith that interface.

Testing indicates that approximately 25 bytes of NVRAM storage are used by this feature per interface. Theremay be some boot delay exhibited on platforms with lower CPU speeds

QUESTION 51Which statement about when you mix TCP and UDP traffic in the same class and overflow occursis true?

A. UDP traffic suffers more, because TCP guarantees delivery.B. TCP traffic is starved, because UDP never slows down when packets get dropped.C. The overflow is not a problem, because both TCP and UDP packets get randomly dropped and

traffic will back out.D. Mixing TCP and UDP in the same class is not supported.



QUESTION 52A provider plans to use IP SLA to help diagnose future performance issues in their PE routers inthe network. Which two should be considered by the provider? (Choose two.)

A. IP SLA requires a significant amount of resources to operate properly. Using IP SLA on the PErouters will only aggravate performance-related issues the network already encounters.

B. IP SLA is supported only on Cisco IOS edge routers, because it simulates traffic from thenetwork endpoints.

C. IP SLA should be implemented on dedicated hardware to properly simulate network endpointsD. IP SLA should use a mix of source and target points.

Correct Answer: CDSection: (none)Explanation



A provider uses the recommended mappings for DSCP to MPLS EXP. Several sites connected tothe same PE router report that critical data has been experiencing a high number of drops. Thecustomer marks its CRITICAL data as AF31. What appears to be the problem?

A. The classification for CRITICAL-DATA should contain a match-all, not a match-any.B. The provider is using the recommended mappings for DSCP to MPLS EXP, so the CLASSMAP

for the CRITICAL-DATA should contain EXP value of 4.C. The recommended mapping for AF31 is to MPLS EXP 5, which is classified in the REALTIME

class, not the CRITICAL DATA class.D. The allocated bandwidth for CRITICAL-DATA should be increased to provide sufficient

bandwidth to support the application.E. If the data receiving drops is high priority, it should be marked with MPLS EXP value 7.





By default, the IP precedence value is copied into the MPLS EXP field during imposition.You can mark theMPLS EXP bits with an MPLS QoS policy.

DSCP CS1 is mapped into EXP 1

QUESTION 54What are three fundamental QoS mechanisms? (Choose three.)

A. congestion avoidanceB. undersubscriptionC. congestion handlingD. policingE. marking

Correct Answer: ADESection: (none)Explanation


QUESTION 55Which three issues are important challenges for monitoring service quality in the SP core network?(Choose three.)

A. Multiple flows compete for a limited amount of bandwidthB. Packets have to traverse many network devices and links that add up to the overall delay.C. Traffic flows are continuously high.D. Packets may have to be dropped when a link is congestedE. Relatively few tools are available for collecting service quality data.




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

A. Traffic is queued using LLQB. 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.

Correct Answer: ABSection: (none)Explanation


QUESTION 57Refer to the exhibit on a PE router. What could be causing the issue?

Service-policy output: OUTPUT-POLICYCounters last updated 00:00:00 agoClass-map: REALTIME (match-any)845206 packets, 348763573 bytes30 second offered rate 3000000 bps, drop rate 2500000 bpsMatch: ip dscp cs5 (40) ef (46)Priority: 10% (500 kbps), burst bytes 327265678, b/w exceed drops: 312925450

Class-map: DSCP-OUT-RTVI (match-any)0 packets, 0 bytes30 second offered rate 0000 bps, drop rate 0000 bpsMatch: ip dscp af41 (0)

Queueingqueue limit 32 packets(queue depth/total drops/no-buffer drops) 0/0/0(pkts output/bytes output) 0/0Class-map: class-default (match-any)0 packets, 0 bytes5 minute offered rate 0000 bps, drop rate 0000 bpsMatch: any

Queueingqueue limit 1024 packetsqueue depth/total drops/no-buffer drops) 0/0/0(pkts output/bytes output) 0/0

A. PE interface was not configured with enough bandwidth.B. Traffic rate CE sent is over the SLA limit.C. PE needs to upgrade to a higher throughput interface.D. CE marked all traffic incorrectly to DSCP 46.E. CE marked all traffic incorrectly to DSCP 46.



QUESTION 58A service provider recently changed from RFC 3270 Uniform mode to Pipe mode. Which threeconsiderations 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 specificQoS 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 theDiffServ policy of the provider.

D. In Uniform mode, when the topmost EXP value is changed, the changed EXP value willpropagate to the original IP precedence or DSCP.


Explanation/Reference:http://www.cisco.com/en/US/tech/tk436/tk428/technologies_tech_note09186a008022ad7e.shtml

QUESTION 59What would be the first step when defining an MQC?

A. Add one or more match commands to classify packets

B. Attach the traffic policy (policy map) to the interface by using the service-policy commandC. Define a traffic class by using the class-map command.D. Apply the commands such as bandwidth, police, and set dscp to enable the QoS feature.E. Create a traffic policy by using the policy-map command





A. The voice class is configured with the priority 128 commandB. The voice class is configured with the bandwidth 128 command.C. The gold class is configured with the priority 100 command.D. The gold class is configured with the bandwidth 100 commandE. The voice class is configured with the police 128 command.

Correct Answer: BD


Explanation/Reference:Originally was A


Which queueing method has been configured?

A. LLQB. CBWFQC. WFQD. MDRRE. priority queueing



QUESTION 62Which two Cisco IOS commands can be used to monitor QoS on a device? (Choose two.)

A. show class-mapB. show qos-mapsC. show policy-mapD. show service-policyE. show qos-interfaceF. show qos-dbl



QUESTION 63A service provider will apply this policy at which of these interfaces?

interface Gi1/1service-policy output SP-POLICY!policy-map SP-POLICYclass TRAFFIC-CLASS-1police rate percent 20 conform-action transmit exceed-action droppriority!class TRAFFIC-CLASS-2bandwidth percent 50queue-limit 800 msrandom-detect exp 3 280 ms 490 ms!class class-defaultqueue-limit 500 msrandom-detect exp 1 200 ms 350 msrandom-detect exp 0 100 ms 200 ms!end-policy-map!class-map match-any TRAFFIC-CLASS-1match dscp ipv4 45 ef cs6match mpls experimental topmost 5 6end-class-map!class-map match-any TRAFFIC-CLASS-2match dscp ipv4 cs2 af21 af23 af31 af32 af33 35 37match mpls experimental topmost 3end-class-map!

A. CE interface toward PEB. PE interface toward CEC. PE interface toward PD. P interface toward PE



QUESTION 64Which three match statements are valid in Cisco IOS XR Software? (Choose three.)

A. match fieldB. match mpls experimental topmostC. match vplsD. match flowE. match qos-groupF. match port-type

Correct Answer: BCESection: (none)Explanation

Explanation/Reference:Fabric QoS policy class maps are restricted to matching a subset of the classification options. These are asfollows:

•precedence•dscp•qos-group•discard-class•mpls experimental topmost

To support QoS on a virtual private LAN service (VPLS)-enabled network, packets can be classifiedbased on these VPLS-specific match criteria:• Match vpls broadcast• Match vpls known• Match vpls unknown• Match vpls multicast


The QoS profile was recently updated to mark VoIP traffic with a DSCP setting of AF41. However,the traffic going to the phones in the 172.19.5.0/24 address space is not being marked properly.What is causing this problem?

A. The traffic policy is not written correctly, which causes the wrong marking to be applied.B. The VoIP classification should be configured before any other classifications, because it is the

highest priority.C. The access list does not properly identify SIP traffic.D. Class typeA markings appear first in the policy map, which causes this marking to be applied.





A. No traffic can be matched to the REALTIME traffic class.B. No traffic can be matched to the VoIP traffic classC. No traffic can be matched to the BULK-DATA traffic class.D. AF11 or AF12 or AF13 marked packets will be matched to the BULK-DATA traffic class.E. The BULK-DATA traffic class is missing the match-any option in the class-map command.




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.



QUESTION 68You work for service provider that employs a four-class service provider QoS model (best effort,bronze, silver, gold). A customer recently reported an issue with high drop rate on a missioncriticaldatabase application in the silver class. The silver class is currently at capacity. The goldclass is currently only used for voice and video conferencing, and has available bandwidth. Theapplication was remapped to the gold class. Which statements are valid alternative options to thisdecision? (Choose two.)

A. Moving to a three-class QoS model would allow for more bandwidth per class and wouldreduce the support of maintaining multiple classes.

B. The provider should consider moving to a six-class QoS model to provide more availableclasses of service to differentiate traffic.

C. In addition to the remapping, the provider would have to change the queue model from WFQ topriority queued

D. Additional bandwidth should have been added to the silver class from one of the lower classesbefore the traffic class was moved.

Correct Answer: BDSection: (none)Explanation


QUESTION 69Which three items are important when monitoring service quality in the SP network? (Choosethree.)

A. The typical cause of QoS issues is intermittent failure of network devices and these areinherently difficult to detect.

B. QoS issues can be difficult to detect when there is not enough traffic to trigger the configuredQoS policy.

C. Establishing alarm thresholds for QoS problems can be complicated.D. QoS support differs from device to device, depending on underlying hardware platforms and

software.E. Collection of data to detect QoS issues is slow and labor-intensiveF. Troubleshooting class map configurations is complex and frequently required

Correct Answer: BCDSection: (none)Explanation


QUESTION 70What are two benefits of the DiffServ model? (Choose two.)

A. Its class-based mechanisms are simple and scale well.B. It provides absolute guarantees of service quality.C. Service quality can be tailored to the needs of many different types of traffic.D. It does not require setting up an end-to-end signaling mechanism.

Correct Answer: CDSection: (none)Explanation


QUESTION 71Which three components would you use to define and apply traffic classification? (Choose three.)

A. route mapB. service policyC. class mapD. route policyE. policy map

Correct Answer: BCESection: (none)Explanation


QUESTION 72Which Cisco IOS IP SLA Probe would you select to identify bottlenecks in the network?

A. ICMP Path JitterB. ICMP EchoC. ICMP Path EchoD. FTP Path Echo



QUESTION 73When 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 networkB. in interfaces in the service provider network incoming from the customer LANC. in the service provider coreD. on output interfaces from the service provider network leading to the customer LAN



QUESTION 74To classify and prioritize traffic according to importance, which three statements are correct?(Choose three.)

A. Each class should be guaranteed at least some bandwidthB. Voice traffic should be given top priority.C. Email should be placed in a best-effort class.D. Critical applications should be given sufficient bandwidth to meet their requirements.E. Video should be placed in the same class as voice.

Correct Answer: BCDSection: (none)Explanation


QUESTION 75Which tool is best suited to provide incident management or trouble ticketing?

A. RemedyB. CiscoWorksC. TivoliD. VoyenceE. Intelliden



QUESTION 76Where would a service provider apply this policy?

interface Gi1/1service-policy output SP-POLICYpolicy-map SP-POLICY

class CLASS-REALTIMEpriorityset cos 5!class CLASS-HIPRIORITYbandwidth remaining percent 75set cos 3!class CLASS-BASICbandwidth remaining percent 20set cos 1!class class-defaultset cos 1!end-policy-map

class-map match-any CLASS-BASICmatch dscp af11 af12 af13end-class-map!class-map match-any CLASS-REALTIMEmatch dscp ef af42 af43end-class-map!class-map match-any CLASS-HIPRIORITYmatch dscp af21 af22end-class-map

A. CE interface toward PEB. PE interface toward CEC. PE interface toward PD. P interface toward PE



QUESTION 77An MPLS VPN customer reports that the VoIP voice quality is very bad for calls across the MPLSVPN. What could be the problem?

A. Traffic shaping is applied to the voice traffic classB. The voice traffic class is using the priority command.C. The voice packets are marked as DSCP EF.D. WRED is not configured for the voice traffic class.E. The voice traffic class is using the default queue size.



QUESTION 78A customer is experiencing poor quality on voice connections coming from a particular branchoffice. Data on the service provider network capacity indicates that the devices serving thatlocation are heavily oversubscribed. It will be months before planned expansions can beimplemented. Which class-based traffic-shaping technique would be appropriate to considerimplementing?

A. shaping to the committed rateB. shaping to the peak rateC. shaping to the observed median rateD. shaping to the configured average rate



QUESTION 79A customer with an unmanaged CE router has reported experiencing poor quality on the videoconferencing and broadcast multimedia applications. To address the issue, the provider hasimplemented shaping on the PE router to "smooth out" speed mismatches in the network. Whichof these is a valid concern with this approach?

A. In addition to shaping, the provider should implement policing so the application can detect thecongestion and throttle traffic.

B. Shaping can only be applied to the outbound interface, which does not prevent the customerfrom flooding the inbound link to the provider.

C. Shaping should only be used in a TCP-based environment where the application can detect thecongestion and adjust. Shaping provides little benefit with UDP applications.

D. While shaping may help the broadcast multimedia application, it could cause additional delay inthe video conferencing application.



QUESTION 80Which two match statements are correct in Cisco IOS Software? (Choose two.)

A. class-map class1match not protocol ip

B. class-map match-none class2match protocol ip

C. class-map class3match dscp af31match dscp af41

D. class-map match-any class3match dscp af31match dscp af41




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

A. BEB. CS1C. CD3D. CS4E. AF31


Explanation/Reference:Short-Pipe mode is useful for ISPs implementing their own QoS policy independent of theircustomer’s QoS policy. The IP Precedence bits on an IP packet are propagated upward intothe label stack as labels are added. When labels are swapped, the existing EXP value is kept.If the topmost EXP value is changed, this change is propagated downward only within the

label stack, not to the IP packet.

QUESTION 82When the RFC 3270 Short Pipe mode is used, the PHB at the egress router is based on which ofthese?

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



Short-Pipe mode is useful for ISPs implementing their own QoS policy independent of theircustomer’s QoS policy. The IP Precedence bits on an IP packet are propagated upward intothe label stack as labels are added. When labels are swapped, the existing EXP value is kept.If the topmost EXP value is changed, this change is propagated downward only within thelabel stack, not to the IP packet.

QUESTION 83When the RFC 3270 Uniform mode is used, the PHB at the egress router is based on which ofthese?

A. The topmost MPLS label EXP value.B. The MPLS VPN label EXP valueC. 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


Explanation/Reference:In Uniform mode, any changes made to the EXP value of the topmost label on a label stackare propagated both upward as new labels are added and downward as labels are removed.The idea here is that the network is a single DiffServ domain, so any changes made to theEXP values on the MPLS packet in transit are supposed to be applied to all labelsunderneath the packet, as well as to the underlying IP packet.The rules for Uniform mode are as follows:• On imposition, copy the DSCP/EXP upward.

• On disposition, copy the removed EXP downward to both IP packet and MPLS (ifstacked).The question of deciding which PHB is applied on label disposition is irrelevant; no matterwhen you apply the PHB according to the received EXP value or the outgoing EXP/DSCPvalue, they’re both the same.


The service provider uses a three-class service provider QoS model (real-time, critical, best effort).The provider receives reports from a customer about poor quality on their multimedia conferences.The provider recently updated their profiles to include multimedia conferencing (af41) to their realtimeclass, which includes voice (ef). What are the two most likely causes of this problem?(Choose two.)

A. The class map for SP-REALTIME does not include the DSCP values for multimediaconferences and voice traffic.

B. The MPLS experimental 3 is in the SP-CRITICAL-DATA class, not the SP_REALTIME class.C. Multimedia conferencing is included in the SP-CRITICAL-DATA class.D. The SP-REALTIME class should include mpls experimental 4, not 5.E. The SP-CRITICAL-DATA class should not use random detect for multimedia traffic.




The voice traffic is not receiving the appropriate per-hop behavior at the egress of the CE-PE link.What is the problem?

A. Both ACLs are misconfigured.B. Both class maps are misconfigured.C. The control traffic class should be configured with the priority command instead of the

bandwidth command.D. Instead of hard coding the actual bandwidth on the priority and bandwidth commands, the

percent option should be used.




A customer reports that data between their sites across your network is very slow and that voiceand video quality are unacceptable. Packet traces of data coming in from and going out to the customer confirmthat many packets are being dropped in your network, and many of those thatare not dropped are being remarked to CS1. Class maps and a policy map configured as shownare applied inbound to the Fast Ethernet interfaces that connect the customer. What could be theproblem?

A. The CIR and PIR values appear to have been configured using kbps when the entries are bps..B. The match criteria is DSCP and the customer packets are being sent marked using IP

precedence.C. All traffic is matching the class class-default, because all other classes are match-all with

multiple match criteria.D. The customer data is being rate limited, but is not being queued by class, which is causing tail

drops and packet remarking.



bucket size in bits per second not kbps 1000 bytes = 8000 bps



A. This is a dual-rate policing example.B. Packets marked with IP Precedence 5 that conforms to the committed rate will be marked with

MPLS EXP 5 then transmitted.C. Packets marked with IP Precedence 5 that exceeds the committed rate will be marked with

MPLS EXP 5.D. This policy will police traffic at the ingress and egress directions.





By default, the IP precedence value is copied into the MPLS EXP field during imposition.You can mark theMPLS EXP bits with an MPLS QoS policy

QUESTION 88A customer reports that during peak hours, FTP performance is unacceptable. Currently, theservice provider maps the customer FTP traffic into the class-default traffic class and FTP traffic ismarked with MPLS EXP1. The class-default class traffic is configured with MPLS EXP basedWRED and also with the bandwidth command. What could be causing the FTP performanceissues with the customer?

A. The FTP-type bulk traffic should be mapped to MPLS EXP 5 instead of MPLS EXP 1. Theimproper marking of FTP packets is causing CBWFQ to assign lower priority for FTP packetswithin the class-default traffic class

B. The service provider is using LLQ on all the core links, but the FTP traffic is not is assigned tothe priority queue.

C. The bandwidth command is causing the FTP issues. It is generally not recommended to useCBWFQ for the class-default traffic class.

D. FTP packets are being more randomly dropped that the other TCP traffic within the classdefaulttraffic class, because the WRED thresholds for MPLS EXP 3 marked packets wereconfigured to improper values.


Explanation/Reference:http://www.ciscopress.com/articles/article.asp?p=28688



A. This example is a dual-bucket policer, and only traffic that exceeds the committed rate will bedropped.

B. This example is a dual-rate policer, and traffic exceeding either the peak or the committed ratewill be dropped.

C. This example is a traffic policer, and three token buckets are used to meter the incoming traffic.D. This example is a traffic policer, and traffic exceeding the committed rate will be buffered until

the congestion is cleared.E. This example is a percentage-based policer, and the configured percentage is referenced to the

input or output queue size.


Explanation/Reference:http://www.cisco.com/en/US/docs/routers/10000/10008/configuration/guides/qos/10qpolce.html

QUESTION 90Drag the definitions from the left onto the traffic classification on the right. Not all definitions will beused.

Select and Place:

Correct Answer:


Explanation/Reference:Explanation: Application that must have guaranteed service mission-criticalDatabase, interactive, or preferred service transactionalInternet, email, unspecified traffic best-effortPeer-to-peer applications scavenger

QUESTION 91Drag and drop mechanisms on the left to their corresponding uses on the right. Somemechanisms may not used

Select and Place:

Correct Answer:


Explanation/Reference:CBWFQ gives critical flows top priorityWRED drops packets as needed to avoid congestionLLQ gives voice traffic top priorityMarking marks best effort traffic for lower priority


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Maintaining Cisco Service Provider Quality of … · Maintaining Cisco Service Provider Quality of ... is easy to design and ... 6/qos/configuration/guide/qc36over.pdf QUESTION 26