Team LiB
Previous Section Next Section

Chapter 3

"Do I Know This Already" Quiz

Cisco Modular QoS CLI

1.

What does MQC stand for?

  1. Multiprotocol QoS Commands

  2. Multiprotocol QoS CLI

  3. Modular QoS Commands

  4. Modular QoS CLI

  5. Modular QoS Convention

Answer:

D

2.

Which of the following MQC commands is most related to the process of classifying packets into service classes?

  1. service-policy

  2. route-map

  3. map-policy

  4. policy-map

  5. map-class

  6. class-map

Answer:

F

3.

Which of the following is not a benefit of MQC?

  1. Reduces configuration time

  2. Provides Modular QoS Call-Admission-Control

  3. Same set of commands on all Cisco IOS platforms

  4. Separates classification from per-hop behavior (PHB) actions

Answer:

B

4.

Which of the following is not true about the mechanics of MQC?

  1. Packets are classified inside a class map.

  2. PHBs are defined inside a service policy.

  3. Matching multiple DSCPs requires multiple match commands.

  4. One command is used to enable a QoS policy on an interface for packets both entering and exiting an interface.

Answer:

B, C, D

PHBs are defined inside a policy-map command. You can match up to eight DSCP values in a single command. A separate service-policy command is required to enable a policy on an interface for each direction of packet flow (in and out).

5.

Examine the configuration snippet that follows. Which of the following statements is true about the configuration?

   Router(config)#class-map fred
   Router(config-cmap)#match dscp EF
   Router(config-cmap)#match access-group 101

  1. Packets with DSCP EF and that also match ACL 101 will match the class.

  2. Packets that either have DSCP EF or that match ACL 101 will match the class.

  3. Packets that match ACL 101 will match the class because the second match command replaces the first.

  4. Packets will match only DSCP EF because the first match exits the class map.

Answer:

A

The class-map command defaults to use the match-all parameter, which means both conditions established by the match command must be true in order to match the class.

Cisco QoS Policy Manager

6.

Which of the following is false about QPM?

  1. Provides a standard set of commands for configuring QoS

  2. Allows a user to specify QoS policies without knowing the MQC command syntax

  3. Graphs QoS performance

  4. Takes advantage of Cisco QoS MIBs

Answer:

A

Cisco AutoQoS Feature

7.

Which option on a 2950 switch auto qos voip command tells the switch to trust the CoS only if a Cisco IP Phone is attached to the port?

  1. trust cos

  2. ciscophone

  3. cisco-phone

  4. ciscoipphone

Answer:

D

8.

Which option on a 6500 switch set port qos command tells the switch to trust the CoS only if a Cisco IP Phone is attached to the port?

  1. trust cos

  2. ciscophone

  3. cisco-phone

  4. ciscoipphone

Answer:

D

9.

Which of the following PHBs cannot be enabled using the AutoQoS VoIP feature on a router?

  1. Low Latency Queuing

  2. CB Marking

  3. Shaping

  4. MLP LFI

  5. Policing

Answer:

E

Policing is enabled as a PHB for 6500 Cat-OS when using the ciscosoftphone option, but not at all on a router with AutoQoS.

10.

Which router commands display the configuration that results from enabling AutoQoS VoIP on a router's S0/0 interface, including the details of any class maps or policy maps?

  1. show autoqos

  2. show auto qos

  3. show auto qos interface s0/0

  4. show running-config

Answer:

B, D

show autoqos is not the correct syntax; show auto qos interface s0/0 does not show the details about any class maps and policy maps.

11.

Which of the following statements are true about requirements before AutoQoS can be enabled on a router interface?

  1. CEF must be enabled unless trust is to be configured.

  2. No service-policy commands can be on the interfaces.

  3. WFQ must be disabled using the no fair-queue command.

  4. HDLC encapsulation must be changed to PPP.

  5. For proper operation, bandwidth should be set to the correct value.

Answer:

A, B, E

Cisco Express Forwarding (CEF) is required when there is no trust.

Comparisons of CLI, MQC, and AutoQoS

12.

Comparing CLI, MQC, and AutoQoS, which is considered to require the least amount of time to implement?

  1. CLI

  2. MQC

  3. AutoQoS

  4. All take equal time

Answer:

C

Q&A

1.

Configure two class maps, one that matches the packets permitted by ACL 101, and one that matches packets denied by ACL 101. Do not use class-default, and do not bother configuring a policy map.

1.

Answer:

 class-map match-all c1
  match access-group 101
 class-map match-all c2
  match not access-group 101

2.

Configure a policy map that refers to predefined classes c1, C2, and c3, with the action for each class map being to set the DSCP value to AF11, AF21, and AF22, respectively. Assume that the class maps are already defined.

2.

Answer:

policy-map fred
 class c1
  set dscp AF11
class C2
 set dscp AF21
class c3
 set dscp AF31

3.

List the three major configuration steps and the main command used in each step for the configuration of a QoS feature using MQC.

Answer:

First, classification is configured with class-map commands. Then, PHBs are configured using a policy-map. Finally, the policy map is enabled for input or output packets on an interface using the service-policy command.

4.

Describe two different ways with which you could classify packets with DSCP AF31, AF32, and AF33 into a single class using MQC commands.

Answer:

Inside a class-map, the match dscp AF31 AF32 AF33 command would match packets that had any of the three DSCP values. Alternately, you could use a class-map with the match-any parameter, followed by three match dscp commands, one for each DSCP value.

5.

List three benefits of MQC as compared with non-MQC-based QoS features.

Answer:

Reduces the effort taken to configure QoS. Configuration of classification and PHBs are separated from the interfaces, allowing more concise configuration and more flexibility. Uniform command syntax across multiple QoS features in a single device. Uniform command syntax across router and IOS-based switch platforms. Class maps are reusable for multiple QoS policy maps.

6.

Consider the configuration snippet that follows. What commands would list statistics for the QoS policy implemented on fastethernet 0/0?

  class-map fred
   match dscp ef
  policy-map barney
   class fred
    set dscp af11
   class class-default
    set dscp be
  interface fastethernet0/0
   service-policy input barney

Answer:

The show policy-map interface fastethernet0/0 command, and the show policy-map interface fastethernet0/0 input command.

7.

List the two SNMP MIBs included in Cisco router IOS that can be used by QPM to improve the statistics presented to a QPM user. List the long version of the names and the acronyms.

Answer:

The Class-Based QoS MIB (CBQoSMIB) and the Cisco NBAR Protocol Discovery (CNPD) MIB.

8.

What information can be seen by using the CBQoSMIB that cannot be seen with show commands on the device being managed?

Answer:

The CBQoSMIB allows you to see statistics about packets before and after the application of a policy.

9.

How many classes can be associated with a single policy map in Cisco IOS Software Release 12.2(15)T?

Answer:

256

10.

On a router using AutoQoS, what command enables the feature for Frame Relay VCs that use Frame Relay-to-ATM service interworking?

Answer:

auto qos voip fr-atm.

11.

On a router using AutoQoS, what command enables the feature on a serial interface when the router can trust the DSCP settings of incoming packets?

Answer:

auto qos voip trust.

12.

Describe the classification configuration created by a router when enabling AutoQoS on a serial interface, with all default values chosen on the auto qos command.

Answer:

The router classifies voice payload into one service class, voice signaling into another, and all other traffic into a third. It uses NBAR and ACL for matching the voice traffic.

13.

Describe the marking actions created by a router when enabling AutoQoS on a serial interface, with all default values chosen on the auto qos command.

Answer:

The router classifies marks voice payload with DSCP EF, voice signaling with DSCP AF31, and all other traffic as DSCP BE.

14.

List three of the requirements on router AutoQoS that need to be true before actually configuring AutoQoS.

Answer:

IP CEF must be enabled on each interface or ATM VC, unless the trust option will be used. The bandwidth command should be configured correctly on each interface or VC. Any existing service-policy commands should be removed from interfaces on which AutoQoS will be enabled. Frame Relay must also use only point-to-point subinterfaces.

15.

List the data link protocols on a router that support AutoQoS.

Answer:

ATM, Frame Relay, HDLC, and PPP.

16.

List the PHBs created by a router when the auto qos voip command is used on a PPP serial interface with the default bandwidth setting.

Answer:

Classification and Marking, Queuing (LLQ)

17.

List the PHBs created by a router when the auto qos voip command is used on a PPP serial interface with bandwidth 768 configured.

Answer:

Classification and Marking, Queuing (LLQ), MLP LFI, and cRTP. All links at 768 kbps or less also have cRTP and LFI added as PHBs.

18.

List the PHBs created by a router when the auto qos voip command is used on a Frame Relay PVC with bandwidth 832 configured.

Answer:

Classification and Marking, Queuing (LLQ), plus Shaping with FRTS. Had bandwidth 768 been configured, Frame Relay fragmentation and cRTP would also have been configured.

19.

When configuring AutoQoS on a router, with a Frame Relay interface, what configuration mode must you be in before using the auto qos command? What command gets you into that configuration mode?

Answer:

You must have used the frame-relay interface-dlci command to get into DLCI configuration mode.

20.

When configuring a 2950 switch with the auto qos voip trust command, what PHBs are configured on the interface?

Answer:

Queuing with queue 4 as the low latency queue, CoS-to-DSCP maps that correlate AF31 to CoS 3 and EF to Cos 5, and the trusting of incoming CoS values.

21.

When configuring a 2950 switch with the auto qos voip cisco-phone command, what PHBs are configured on the interface?

Answer:

Queuing with queue 4 as the low latency queue, CoS-to-DSCP maps that correlate AF31 to CoS 3 and EF to CoS 5, and the trusting of incoming CoS values. However, it also includes extending the trust boundary to the IP Phone, so if an IP Phone is not found, all frames are considered to be CoS 0.

22.

When configuring a 2950 switch with the auto qos voip cisco-phone command, what version of CDP is required in order for AutoQoS to work?

Answer:

CDP Version 2.

23.

When planning to use AutoQoS on a 2950 switch, what types of ports are generally configured with the trust option, and what type are generally configured with the cisco-phone option?

Answer:

Ports that are connected to end users are configured with cisco-phone. Ports connected via 802.1Q trunks to other switches (or to trusted servers), for which those switches or servers have already marked CoS correctly, are configured with the trust option.

24.

When using AutoQoS on a 6500 running Cat-OS, describe the difference in using the ciscosoftphone setting and the trust dscp setting.

Answer:

Both cause a port to trust DSCP, but with ciscosoftphone, AutoQoS also configures policing, preventing the device on the port from sending more traffic as DSCP EF than the SoftPhone application can send.

25.

When using AutoQoS on a 6500 running Cat-OS, describe when you might choose to use the ciscosoftphone option versus the trust dscp option.

Answer:

trust dscp is typically used when the the engineer knows that the DSCP of incoming frames should have already been set correctly based on QoS policies. ciscosoftphone is used when a PC with the Cisco soft phone application has been installed on the PC.

26.

When using AutoQoS on a 6500 running Cat-OS, describe when you might choose to use the ciscoipphone setting versus the trust cos setting.

Answer:

trust cos is typically used when the the engineer knows that the CoS of incoming frames should have already been set correctly based on QoS policies. ciscoipphone is used on most ports connected to end users, if an IP Phone might be installed.

27.

When using AutoQoS on a 6500 running Cat-OS, the set port qos autoqos 3/1 voip ciscoipphone command has been configured. Describe what else must be true before AutoQoS will trust incoming CoS values for frames on port 3/1.

Answer:

CDP version 2 must be enabled on the port. Also, CDP must recognize the presence of a Cisco IP Phone on the port. At that point, the switch will trust the marked CoS of incoming frames.

28.

Comparing the CLI of older QoS options in a Cisco router, MQC, and AutoQoS, which takes the least time to implement?

Answer:

AutoQoS.

29.

Comparing the CLI of older QoS options in a Cisco router, MQC, and AutoQoS, which is considered to be the most modular?

Answer:

AutoQoS and MQC are both modular, whereas older QoS features that do not use MQC are not.

30.

Comparing the CLI of older QoS options in a Cisco router, MQC, and AutoQoS, which is considered to be the most difficult to use?

Answer:

CLI.

    Team LiB
    Previous Section Next Section