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QUESTION 82
When the RFC 3270 Short 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
Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Short-Pipe mode is useful for ISPs implementing their own QoS policy independent of their customer’s QoS policy. The IP Precedence bits on an IP packet are propagated upward into the 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 83
When the RFC 3270 Uniform 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
Correct Answer: A Section: (none) Explanation
Explanation/Reference:
In Uniform mode, any changes made to the EXP value of the topmost label on a label stack
are 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 the
EXP values on the MPLS packet in transit are supposed to be applied to all labels
underneath 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 (if stacked). The question of deciding which PHB is applied on label disposition is irrelevant; no matter when you apply the PHB according to the received EXP value or the outgoing EXP/DSCP
value, they’re both the same.
QUESTION 84
Refer to the exhibit.
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 realtime
class, 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 multimedia conferences 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.
Correct Answer: AC Section: (none) Explanation
Explanation/Reference:
QUESTION 85
Refer to the exhibit.
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.
Correct Answer: B Section: (none)
Explanation Explanation/Reference:
QUESTION 86
Refer to the exhibit.
A customer reports that data between their sites across your network is very slow and that voice and video quality are unacceptable. Packet traces of data coming in from and going out to the customer confirm that many packets are being dropped in your network, and many of those that are not dropped are being remarked to CS1. Class maps and a policy map configured as shown are applied inbound to the Fast Ethernet interfaces that connect the customer. What could be the problem?
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.
Correct Answer: A Section: (none) Explanation
Explanation/Reference:
bucket size in bits per second not kbps 1000 bytes = 8000 bps
QUESTION 87
Refer to the exhibit.
Which statement is correct?
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.
Correct Answer: B Section: (none) Explanation
Explanation/Reference: MPLS Experimental Field
Setting the MPLS experimental (EXP) field value satisfies the requirement of service providers who do not want the 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 priority that they require during periods of congestion.
By default, the IP precedence value is copied into the MPLS EXP field during imposition.You can mark the MPLS EXP bits with an MPLS QoS policy
QUESTION 88
A customer reports that during peak hours, FTP performance is unacceptable. Currently, the service provider maps the customer FTP traffic into the class-default traffic class and FTP traffic is marked with MPLS EXP1. The class-default class traffic is configured with MPLS EXP based WRED and also with the bandwidth command. What could be causing the FTP performance issues with the customer?
A. The FTP-type bulk traffic should be mapped to MPLS EXP 5 instead of MPLS EXP 1. The improper marking of FTP packets is causing CBWFQ to assign lower priority for FTP packets within 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 to the priority queue.
C. The bandwidth command is causing the FTP issues. It is generally not recommended to use CBWFQ for the class-default traffic class.
D. FTP packets are being more randomly dropped that the other TCP traffic within the classdefault traffic class, because the WRED thresholds for MPLS EXP 3 marked packets were configured to improper values.
Correct Answer: D Section: (none) Explanation
Explanation/Reference:
http://www.ciscopress.com/articles/article.asp?p=28688
QUESTION 89
Refer to the exhibit.
Which statement is correct?
A. This example is a dual-bucket policer, and only traffic that exceeds the committed rate will be dropped.
B. This example is a dual-rate policer, and traffic exceeding either the peak or the committed rate will 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.
Correct Answer: B Section: (none) Explanation
Explanation/Reference:
http://www.cisco.com/en/US/docs/routers/10000/10008/configuration/guides/qos/10qpolce.html
QUESTION 90
Drag the definitions from the left onto the traffic classification on the right. Not all definitions will be used.
Select and Place:
Correct Answer:
Section: (none) Explanation
Explanation/Reference:
Explanation: Application that must have guaranteed service mission-critical Database, interactive, or preferred service transactional Internet, email, unspecified traffic best-effort Peer-to-peer applications scavenger
QUESTION 91
Drag and drop mechanisms on the left to their corresponding uses on the right. Some mechanisms may not used
Select and Place:
Correct Answer:
Section: (none) Explanation
Explanation/Reference:
CBWFQ gives critical flows top priority WRED drops packets as needed to avoid congestion LLQ gives voice traffic top priority Marking marks best effort traffic for lower priority
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