Braindumps of 642-642
Quality of Service
Exam Questions, Answers, Braindumps (642-642)
Check some 642-642 questions. These will help for
1: Based on the Cisco Catalyst 2950 Series switch
configuration shown, with no weights being assigned
to the egress queues, which type of queuing is being
implemented? wrr-queue cos-map 1 0 wrr-queue cos-map
2 1 2 3 wrr-queue cos-map 3 4 5 wrr-queue cos-map
4 6 7
A. weighted round robin
D. weighted fair
E. weighted round robin with an expedite queue
F. modified deficit round robin
2: What makes the DiffServ model more scalable than
the IntServ model? (Choose all that apply.)
A. DiffServ makes use of per-aggregate QoS instead
of per-flow QoS.
B. DiffServ makes use of hop-by-hop signaling which
allows DiffServ to scale to a larger number of application
C. DiffServ is capable of implementing admission control
either locally on the routers or be offloaded to a
central policy server using the COPS protocol.
D. DiffServ routers are not compelled to track the
state information for each individual flow.
Answer: A, D.
B. No hop-by-hop signaling uses per-hop behavior
C. This is a feature of both models
Sources: Cisco IP QoS Introduction
http://www.cisco.com/en/US/tech/ CK5 43/ CK7 66/technologies_white_paper09186a00800a3e2f.shtml
3: Which of the following statements are true when
you compare DSCP and IP Precedence to each other?
(Choose all that apply.)
A. DSCP is backwards compatible with IP Precedence.
B. DSCP cannot be easily mapped into QoS because of
its expanded classification options.
C. DSCP is more granular the IP Precedence, since
more marking combinations are available.
D. DSCP appears stubby when compared IP Precedence,
since devices make use of DSCP as defined in RFC exclusively.
E. DSCP is 6 bits long and IP Precedence is 3 bits
F. DSCP is more restrictive than IP Precedence, since
devices are only allowed to use DSCP as defined in
Answer: A, C, E.
A)DSCP is backward compatible with IP Precedence (Class
Selector Code point, RFC 1812) but not with the ToS
byte definition from RFC 791 ("DTR" bits)
Introduction to IP QoS (Course) p.45
4: Which MQC command would you use to perform marking
A. precedence 5
B. ip precedence 5
C. set ip precedence 5
D. set ip mark precedence 5
E. mark ip precedence 5
IP precedence is encoded into the three high-order
bits of the ToS field in the IP header. It supports
eight classes of which two are reserved and should
not be used for user-defined classes (IP precedence
6 and 7). IP precedence 0 is the default value and
is usually used for the best-effort class. The set
ip precedence command marks packets of a class with
the specified precedence value.
Introduction to IP QoS (Course) p.9-104
5: Which of the following statements aptly describes
a network well designed for QoS?
A. Packets are classified at each router, based on
as many detail as possible, typically using extended
IP ACLs to match the packets for classification.
B. Packets are classified at each router, based on
socket address only, typically using extended IP ACLs
to match the packets for classification.
C. Packets are classified and marked, close to the
edge of the network. The packets are treated differently
based on this marking at the routers in the middle
of the network.
D. Packets are classified based on different parameters,
but close to the edge of the network. The packets
are automatically characterized based on flow at the
E. Packets are classified based on socket address,
at the router closest to the source of the traffic.
The packets are automatically characterized based
on flow at the routers.
To achieve the same level of quality in both directions
the packets going to and coming from the customer
network must first be classified and marked.
Classification and marking packets going to the customer
network is a more difficult task because:
1) Classifying and marking must be performed on all
2) Classifying and marking requires the identification
of the customer network. Using PBR, CAR, CB-Policing
or CB-Marking does not scale because it involves the
use of access lists (this is especially difficult
if customer networks are dynamically learned via BGP).
Introduction to IP QoS (Course) p.2-35
6: How many possible meaningful values are defined
in the DSCP in a Differentiated Services environment?
DSCP supports more classes (64) than IP precedence
Introduction to IP QoS (Course) p.36
7: Which of the following features will allow the
marking of packets according to the Cisco QoS Framework?
(Choose all that apply.)
Answer: A, D
The Modular Quality of Service Command Line Interface
(MQC) was introduced to allow any supported classification
to be used with any QoS mechanism.
Some mechanisms have the capability to mark packets
based on classification and/or metering (e.g. CAR,
class-based marking, etc.)
Introduction to IP QoS (Course) p.61
8: Which of the following can be classified as Call
Admission Control methods? (Choose all that apply.)
B. Advanced Busyout Monitor
E. Max Connections
Answer: B, C, E.
9: What are the benefits, as listed in the DQOS course,
for Enterprise Networks when QoS is implemented? (Choose
all that apply.)
A. It decreases propagation delay.
B. It provides predictable response times.
C. It prevents the need to increase bandwidth.
D. It supports dedicated bandwidth per application.
E. It maximizes loss during bursty congestion.
Answer: B, D
QoS attemts to solve network traffic performance issues,
although QoS is not a cure-all. To improve network
performance, QoS features affect a network by manipulation
the following network characteristics:
3) Jitter (delay variation)
4) Packet loss
Cisco Press - DQOS Exam Certification Guide p.9
10: Which of the following is most likely to occur
for voice in the absence of QoS? (Choose all that
A. choppy speech
B. words out of order due to recovery
C. disconnect calls
D. unsynchronized voice patterns
E. softer volume speech
Answer: A, C
The following most likely occurs for voice in absence
Voice is hard to understand; voice breaks up, sound
choppy; calls are disconnected; large delay make it
difficult to know when the other caller has finished
Cisco Press - DQOS Exam Certification Guide p.765
11: Auto QoS is which type of Cisco IOS command?
E. serial interface only
To install the quality-of-service (QoS) class maps
and policy maps created by the AutoQoS for the Enterprise
feature, use the auto qos command in interface configuration
mode. To remove the QoS policies, use the no form
of this command.
12: Which two components are associated with the DiffServ
model? (Choose two.)
A. hop-by-hop signaling
B. per-hop behavior
D. Hard QoS
E. DSCP use of class selector
Answer: B, E
The Differentiated Services (DiffServ) model describes
services associated with traffic classes. Traffic
classes are identified by the value of the DiffServ
Code Point (DSCP replaces IP precedence in the ToS
field of the IP header).
The main goal of the DiffServ model are to provide
scalability and a similar level of QoS to the Int
Serv model, without having to do it on a per-flow
basis. The network simply identifies a class (not
application) and applies the appropriate per-hop behavior
Introduction to IP QoS (Course) p.34
Not A: DiffServ does not have signaling
13: What is true about a DSCP marked packet when it
reaches an IP precedence based device?
A. The eight DSCP bits are all set to zero.
B. The last three bits of the DSCP are set to 101.
C. The 8 DSCP AF classes will be mapped into the 8
levels of IP precedence.
D. Bits 7-5 of DSCP have the same position and meaning
as IP precedence.
Cisco Press - DQOS Exam Certification Guide p.120