CCNA 4 v6 Chapter 6: Check Your Understanding Questions Answers

CCNA 4 v6.0 (Connecting Networks v6) Chapter 6: Quality of Service: Check Your Understanding Questions Answers

1. Under which condition does congestion occur on a converged network with voice, video, and data traffic?

  • If a user downloads a file that exceeds the file limitation that is set on the server
  • If the request for bandwidth exceeds the amount of bandwidth available
  • If video traffic requests more bandwidth than voice traffic requests
  • If voice traffic latency begins to decrease across the network

Explanation: Traffic requires enough bandwidth to support services. When there is not enough bandwidth, congestion occurs and typically results in packet loss.

2. What functionality is required on routers to provide remote workers with VoIP and video-conferencing capabilities?

  • IPsec
  • PPPoE
  • QoS
  • VPN

Explanation: Quality of service (QoS) needs to be enabled on routers to provide support for VoIP and video conferencing. QoS refers to the capability of a network to provide better service to selected network traffic, as required by voice and video applications.

3. What happens when a router interface ingress queue is full and new network traffic is received?

  • The router sends the received traffic immediately.
  • The router will drop the arriving packets.
  • The router drops all traffic in the queue.
  • The router queues the received traffic while sending previously received traffic.

Explanation: When the volume of traffic is greater than what can be transported across the network, devices queue, or hold, the packets in memory until resources become available to transmit them. If the number of packets to be queued continues to increase, the memory within the device fills up and packets are dropped.

4. Which queuing method provides user-defined traffic classes where each traffic class has a FIFO queue?

  • CBWFQ
  • FIFO
  • WFQ
  • WRED

Explanation: CBWFQ extends the standard WFQ functionality to provide support for user-defined traffic classes. A FIFO queue is reserved for each class, and traffic belonging to a class is directed to the queue for that class.

5. Which type of traffic does Cisco recommend be placed in the strict priority queue (PQ) when low latency queuing (LLQ) is being used?

  • Data
  • Management
  • Video
  • Voice

Explanation: With LLQ, delay-sensitive data is sent first, before packets in other queues are treated. Although it is possible to enqueue various types of real-time traffic to the strict priority queue, Cisco recommends that only voice traffic be directed to the priority queue.

6. What is the default queuing method used on the LAN interfaces of Cisco devices?

  • CBWFQ
  • FIFO
  • LLQ
  • WFQ

Explanation: When no other queuing strategies are configured, all interfaces except serial interfaces at E1 (2.048 Mb/s) and below use FIFO by default. Serial interfaces at E1 and below use WFQ by default.

7. What is the default queuing method used on the slower WAN interfaces of Cisco devices?

  • CBWFQ
  • FIFO
  • LLQ
  • WFQ

Explanation: When no other queuing strategies are configured, all interfaces except serial interfaces at E1 (2.048 Mb/s) and below use FIFO by default. Serial interfaces at E1 and below use WFQ by default.

8. Which model is the only QoS model with no mechanism to classify packets?

  • Best effort
  • DiffServ
  • Hard QoS
  • IntServ

Explanation: The best-effort model has no way to classify packets; therefore, all network packets are treated the same way. Without QoS, the network cannot tell the difference between packets and, as a result, cannot treat packets preferentially.

9. What happens when an edge router using IntServ QoS determines that the data pathway cannot support the level of QoS requested?

  • Data is forwarded along the pathway using a best-effort approach.
  • Data is forwarded along the pathway using DiffServ.
  • Data is not forwarded along the pathway.
  • Data is forwarded along the pathway using IntServ but not provided preferential treatment.

Explanation: IntServ uses the Resource Reservation Protocol (RSVP) to signal the QoS needs of an application’s traffic along devices in the end-to-end path through the network. If network devices along the path can reserve the necessary bandwidth, the originating application can begin transmitting. If the requested reservation fails along the path, the originating application does not send any data.

10. Which statement describes the QoS classification and marking tools?

  • Classification is performed after traffic is marked.
  • Classification should be done as close to the destination device as possible.
  • Marking is the adding of a value to a packet header.
  • Marking is the identification of which QoS policy should be applied to specific packets.

Explanation: Marking means that you are adding a value to the packet header. Devices receiving the packet look at this field to see whether it matches a defined policy. Marking should be done as close to the source device as possible. This establishes the trust boundary.

11. Which device would be classified as a trusted endpoint?

  • Firewall
  • IP conferencing station
  • Router
  • Switch

Explanation: Trusted endpoints have the capabilities and intelligence to mark application traffic to the appropriate Layer 2 CoS and/or Layer 3 DSCP values. Examples of trusted endpoints include IP phones, wireless access points, video-conferencing gateways and systems, IP conferencing stations, and more.

12. How many bits are used to identify the class of service (CoS) marking in a frame?

  • 3
  • 8
  • 24
  • 64

Explanation: The 802.1p standard uses the first three bits in the Tag Control Information (TCI) field. Known as the Priority (PRI) field, this 3-bit field identifies the class of service (CoS) markings. Three bits means that a Layer 2 Ethernet frame can be marked with one of eight levels of priority (values 0–7).

13. How many levels of priority are possible when using class of service (CoS) marking on frames?

  • 3
  • 8
  • 24
  • 64

Explanation: RFC 2474 redefines the ToS field with a new 6-bit Differentiated Services Code Point (DSCP) QoS field. Six bits offers a maximum of 64 possible classes of service.


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