QoS

Question 1

The measure of transmission quality and service availability of a network

Answer 1

QoS

Question 2

Not real-time traffic. Bursty and widely varying packet arrival times.

Answer 2

Data Traffic

Question 3

Real-time traffic. Constant and predictable bandwidth and packet arrival times. Packets are small but are delay sensitive and should be less than 150 ms.

Answer 3

Voice Traffic

Question 4

Varied bandwidth requirements, can be real time but not always

Answer 4

Video Traffic

Question 5

What are the quality issues in converged networks?

Answer 5

Lack of bandwidth End-to end delay Variation of delay (jitter) Packet loss

Question 6

What QoS mechanism identifies and categorizes traffic into classes?

Answer 6

Classification and marking

Question 7

QoS mechanism that controls the maximum rate of traffic sent or received on an interface.

Answer 7

Policing

Question 8

What is the difference between policing and shaping?

Answer 8

Policing drops exceeding traffic

Shaping delays exceeding traffic

Question 9

What QoS mechanism uses class-based weighted fair queue, which guarantees specific amount of bandwidth to different classes of traffic?

Answer 9

CBWFQ

Question 10

Often configured on interfaces at the edge of a network to limit traffic and is typically used by service providers to offer customers sublate access

Answer 10

Policing

Question 11

Bandwidth assigned to a class is the _____ bandwidth allocated to the class during congestion.

Answer 11

minimum

Question 12

What congestion management or scheduling feature prioritizes voice traffic so it gets to the final destination first

Answer 12

Low-latency queue

Question 13

QoS feature that allows certain types of connections, such as WAN links, to be provisioned with special traffic handling tools such as fragmentation.

Answer 13

Link-specific tools

Question 14

A point in the network where packet markings are not necessarily trusted

Answer 14

Trust boundary

Question 15

The network locations where packet markings are accepted and acted upon

Answer 15

Borders of a trust domain

Question 16

Devices with user access such as PCs and printers are classified under the _____ domain

Answer 16

untrusted

Question 17

Part of the network with only network administrator access such as routers and switches.

Answer 17

trusted domains

Question 18

Tool that inspects packets within a field to identify the type of traffic that the packet is carrying

Answer 18

Classifier

Question 19

What are the four policy-enforcement mechanisms?

Answer 19

Marking

Queing

Policing

Shaping

Question 20

Tool that writes a value in the header of a packet, frame, cell, tag, or label

Answer 20

Marker

Question 21

Layer 2 Ethernet marking that contains three bits to mark the Ethernet frames

Answer 21

Class of Service (CoS)

Question 22

Describes a 3-bit field in the QoS control field of wireless frames

Answer 22

Traffic Identifier (TID)

Question 23

Generally used to indicate the Layer 3 packet field. Comprised of 8 bits, 3 of which are designated as the IP precedence field

Answer 23

ToS (Type of Service)

Question 24

Set of 6-bit values that is used to describe the meaning of ToS. It is backwards compatible with IP precendence.

Answer 24

DSCP (Differentiated services code point)

Question 25

Where should classification and marking be performed?

Answer 25

Close to end devices

Question 26

What are the three most common ways to classify traffic?

Answer 26

Markings Addressing Application signatures

Question 27

Router needs to inspect traffic beyond layer 4

Answer 27

Deep packet inspection

Question 28

Tool that recognizes well known applications

Answer 28

Network Based Application Recognition (NBAR)

Question 29

How does NBAR recognize packets?

Answer 29

By examine the data payload

Question 30

Smoothes out traffic and if it exceeds the offered bandwidth, it buffers or delays it.

Answer 30

Shapers

Question 31

Where should policers be placed to drop traffic as soon as possible so it doesn't waste resources?

Answer 31

ingress

Question 32

When traffic exceeds the allotted bandwidth, what can policers do with the traffic?

Answer 32

Drop or re-mark

Question 33

When congestion occurs, packets get ordered in output buffers

Answer 33

Queuing

Question 34

Decides which packet should be sent out next and occurs regardless of whether there is congestion

Answer 34

Scheduling

Question 35

What are the three scheduling mechanisms?

Answer 35

Strict priority Round-robin Weighted fair

Question 36

Queues with lower priority are only served when the higher priority queues are empty. There is a risk that lower priority traffic will never be processed (traffic starvation)

Answer 36

Strict priority

Question 37

Packets in queues are served in a set sequence

Answer 37

Round-robin

Question 38

Queues are weighted so that some are served more frequently than others. Solves starvation and also gives priority to real time traffic

Answer 38

Weighted fair

Question 39

What queueing mechanism guarantees fair bandwidth for traffic classes. No latency guarantees and is only suitable for data networks

Answer 39

Class-based weighted fair queuing

Question 40

Takes the class-based weighted fair and adds a queue with strict priority for real time traffic

Answer 40

Low-latency queueing

Question 41

Default queuing response to congestion and drops packets as they arrive

Answer 41

Tail drop

Question 42

Congestion avoidance mechanism that randomly drops packets before the queue fills up. Randomness is skewed by traffic weights.

Answer 42

WRED

Question 43

Monitors the buffer depth and performs early discards on random packets.

Answer 43

Random Early Detection

Question 44

What three features are properties and one-way requirements for voice traffic?

Answer 44

Smooth Latency below 150ms 30-128 kbps Jitter \<30ms

Question 45

Where does Cisco recommend that traffic be classified and marked?

Answer 45

As close as possible to the network edge

Question 46

The trust boundary lies between the _____ interface of the device that will trust the QoS markings and the _____ interface of the device marking the traffic.

Answer 46

ingress egress

Question 47

Smooths out temporary bursts of traffic and enables a network interface to more efficiently handle traffic flows whose combined rates approach the maximum bandwidth available on the interface.

Answer 47

shaping

Question 48

You have enabled QoS on a Cisco router. The router receives marked traffic on an interface that uses the default settings. What will occur?

Answer 48

Traffic will be classified and re-marked without regard to QoS markings

Question 49

Where does the trust boundary lie?

Answer 49

Between ingress interface of device that will trust the QoS markings and the egress interface of the device marking the traffic

Question 50

By default, how are ports marked when QoS is first enabled?

Answer 50

untrusted

Question 51

What do OSI Layer 2 QoS markings such as Ethernet Class of Service (CoS) values do?

Answer 51

Enable devices incapable of accessing Layer 3 header information to make informed QoS decisions

Question 52

A queuing system has three queues serviced with round robin scheduling and one low latency queue that holds all voice traffic. Round robin queue 1 holds predominantly UDP traffic, while round robin queues 2 and 3 hold predominantly TCP traffic. The packets in each queue happen to have a variety of DSCP markings per the QoS design. In which queues would it make sense to use a congestion avoidance (drop management) tool?

Answer 52

Queues 2 and 3 Drop management relies on the behavior of TCP, in that TCP connections slow down sending packets due to the TCP congestion window calculation. Voice traffic uses UDP, and the question states that queue 1 uses UDP. So, queues 2 and 3 are reasonable candidates for using a congestion management tool.

Question 53

On networks that utilize Low Latency Queuing (LLQ), _____ is a common problem that can be seen under times of high network load. In these circumstances the routers will always give preference to the voice or video traffic classified into the LLQ, leaving all other traffic to sit idle in a queue.

Answer 53

queue starvation

Question 54

You want to guarantee that more important traffic will always be sent before less important traffic. What are you most likely to configure?

Answer 54

priority queuing

Question 55

What are the four basic queuing mechanisms available on most Cisco hardware platforms?

Answer 55

FIFO (First in First out), PQ (Priority Queuing), Custom queuing (CQ), weighted fair

Question 56

What type of queuing mechanism does the packet exit a queue in the same order that they entered?

Answer 56

FIFO

Question 57

What is the downside of using FIFO?

Answer 57

Can introduce considerable amounts of delay and jitter because of the inherent lack of prioritization.

Question 58

What queuing is generally used by default on Cisco devices?

Answer 58

FIFO

Question 59

What protocol is used to mitigate VoIP quality problems and can reserve bandwidth along an entire path?

Answer 59

RSVP (Resource Reservation Protocol)

Question 60

Where is traffic policing typically implemented?

Answer 60

ingress traffic to limit the amount of processing for traffic that will inevitably be discarded

Question 61

Implemented on egress traffic to maintain service level agreements (SLAs) and optimize available bandwidth without exceeding a configured committed access rate (CAR).

Answer 61

Traffic shaping

Question 62

Which statement about QoS default behavior is true? - Ports are untrusted by default - VoIP traffic is passed without being tagged - Video trafic is passed with well-known DSCP value of 46 - Packets are classified internally with an environment - Packets that arrive with a tag are untagged at the edge of administrative domain

Answer 62

Packets that arrive with a tag are untagged at the edge of administrative domain

Question 63

Which option describes the purpose of traffic policing? It prioritizes routing protocol traffic It remarks traffic that is below the CIR It drops traffic that exceeds the CIR It queues and then transmits traffic that exceeds the CIR

Answer 63

It drops traffic that exceeds the CIR

Question 64

Which statement about QoS default behavior is true? A. Ports are untrusted by default. B. VoIP traffic is passed without being tagged. C. Video traffic is passed with a well-known DSCP value of 46. D. Packets are classified internally with an environment. E. Packets that arrive with a tag are untagged at the edge of an administrative domain.

Answer 64

E. Packets that arrive with a tag are untagged at the edge of an administrative domain.