Automation and Quality of Service practice questions

Study all Automation and Quality of Service common traps →

A service provider is implementing QoS on an MPLS network to support voice, video, and data traffic. Which queuing mechanism provides the lowest latency for real-time traffic?

Trap 1: FIFO

FIFO provides no traffic differentiation, leading to unpredictable latency.

Trap 2: WRED

WRED is a congestion avoidance mechanism that drops packets probabilistically, not a queuing mechanism.

Trap 3: CBWFQ

CBWFQ uses class-based weighted fair queuing but does not provide a strict priority queue for real-time traffic.

A
FIFO
Why wrong: FIFO provides no traffic differentiation, leading to unpredictable latency.
B
WRED
Why wrong: WRED is a congestion avoidance mechanism that drops packets probabilistically, not a queuing mechanism.
C
LLQ
LLQ provides a strict priority queue that ensures low latency and jitter for real-time traffic.
D
CBWFQ
Why wrong: CBWFQ uses class-based weighted fair queuing but does not provide a strict priority queue for real-time traffic.

Question 2mediummultiple choice

Study all Automation and Quality of Service common traps →

An engineer is troubleshooting a QoS policy on a Cisco router. The policy is intended to mark voice traffic with DSCP EF and video traffic with DSCP AF41. After applying the policy, voice traffic is correctly marked, but video traffic is marked as DSCP 0. What is the most likely cause?

Trap 1: The video traffic is being policed and dropped.

Policing would drop or mark down traffic, not reset to DSCP 0.

Trap 2: The trust boundary is set to 'trust dscp' and the incoming video…

Trust boundary would preserve the incoming marking, not reset to 0.

Trap 3: The policy is not applied to the correct interface direction.

If the policy were misapplied, no traffic would be marked, not just video.

A
The class map for video traffic does not match the traffic correctly.
A misconfigured match statement would cause video traffic to fall into the default class, resulting in DSCP 0.
B
The video traffic is being policed and dropped.
Why wrong: Policing would drop or mark down traffic, not reset to DSCP 0.
C
The trust boundary is set to 'trust dscp' and the incoming video traffic is not marked.
Why wrong: Trust boundary would preserve the incoming marking, not reset to 0.
D
The policy is not applied to the correct interface direction.
Why wrong: If the policy were misapplied, no traffic would be marked, not just video.

Question 3hardmultiple choice

Study all Automation and Quality of Service common traps →

A service provider uses an MPLS-TE tunnel to carry voice and data traffic. The tunnel is experiencing packet loss during congestion. The engineer wants to ensure that voice traffic receives guaranteed bandwidth and low latency while data traffic uses remaining bandwidth. Which QoS configuration should be applied on the tunnel interface?

Trap 1: CBWFQ with bandwidth allocation for voice and data

CBWFQ does not provide strict priority for voice, potentially causing latency.

Trap 2: Policing on voice traffic to limit its rate

Policing discards excess traffic but does not guarantee bandwidth or low latency.

Trap 3: Shaping on the tunnel to 75% of bandwidth with no queuing

Shaping without queuing does not prioritize voice over data.

A
LLQ with a priority queue for voice and a default class for data
LLQ ensures low latency for voice, and the default class uses remaining bandwidth for data.
B
CBWFQ with bandwidth allocation for voice and data
Why wrong: CBWFQ does not provide strict priority for voice, potentially causing latency.
C
Policing on voice traffic to limit its rate
Why wrong: Policing discards excess traffic but does not guarantee bandwidth or low latency.
D
Shaping on the tunnel to 75% of bandwidth with no queuing
Why wrong: Shaping without queuing does not prioritize voice over data.

Question 4easymultiple choice

Study all Automation and Quality of Service common traps →

An engineer is configuring MPLS VPN and needs to ensure that customer traffic is automatically marked with a specific QoS policy based on the VPN. Which method should be used to propagate QoS markings across the MPLS network?

Trap 1: Use 802.1p CoS on the CE-PE link and preserve it across the MPLS…

CoS is not preserved across MPLS backbone without mapping.

Trap 2: Use IP ToS bits to mark traffic and rely on MPLS to preserve them

IP ToS bits are often overwritten by MPLS.

Trap 3: Set DSCP at the ingress PE and preserve it across the MPLS backbone

DSCP may not be preserved across MPLS unless explicitly configured.

A
Use 802.1p CoS on the CE-PE link and preserve it across the MPLS backbone
Why wrong: CoS is not preserved across MPLS backbone without mapping.
B
Use MPLS EXP bits to mark traffic at the ingress PE and map to QoS at egress
MPLS EXP bits are designed to carry QoS information across the MPLS network.
C
Use IP ToS bits to mark traffic and rely on MPLS to preserve them
Why wrong: IP ToS bits are often overwritten by MPLS.
D
Set DSCP at the ingress PE and preserve it across the MPLS backbone
Why wrong: DSCP may not be preserved across MPLS unless explicitly configured.

Question 5mediummultiple choice

Study all Automation and Quality of Service common traps →

A network administrator configures a class map to match VoIP traffic using 'match ip dscp ef' on a Cisco router. However, the QoS policy is not applying the expected marking to VoIP packets. What is a possible reason?

Trap 1: The policy is applied in the output direction instead of input.

The direction would affect all traffic, not just VoIP.

Trap 2: The policy is applied to the wrong interface.

If the policy were on the wrong interface, no traffic would be affected.

Trap 3: The class map uses the wrong match type.

The match type is correct for DSCP.

A
The policy is applied in the output direction instead of input.
Why wrong: The direction would affect all traffic, not just VoIP.
B
The VoIP traffic is not marked with DSCP EF from the source.
If the source does not set DSCP EF, the match will fail and the traffic will not be classified.
C
The policy is applied to the wrong interface.
Why wrong: If the policy were on the wrong interface, no traffic would be affected.
D
The class map uses the wrong match type.
Why wrong: The match type is correct for DSCP.

Question 6mediummulti select

Study all Automation and Quality of Service common traps →

Which TWO QoS mechanisms are used to provide congestion avoidance? (Choose two.)

Trap 1: Policing

Policing is a traffic conditioning mechanism, not congestion avoidance.

Trap 2: CBWFQ

CBWFQ is a queuing mechanism.

Trap 3: LLQ

LLQ is a queuing mechanism that provides strict priority.

A
Policing
Why wrong: Policing is a traffic conditioning mechanism, not congestion avoidance.
B
RED
RED (Random Early Detection) is a congestion avoidance mechanism.
C
CBWFQ
Why wrong: CBWFQ is a queuing mechanism.
D
LLQ
Why wrong: LLQ is a queuing mechanism that provides strict priority.
E
WRED
WRED (Weighted Random Early Detection) drops packets probabilistically to avoid congestion.

Question 7hardmulti select

Study all Automation and Quality of Service common traps →

Which THREE statements about implementing QoS in an MPLS VPN environment are correct? (Choose three.)

Trap 1: QoS policies cannot be applied to MPLS interfaces due to label…

QoS policies can be applied to MPLS interfaces, often using EXP-based classification.

Trap 2: 802.1p CoS marking is preserved across the MPLS backbone by default.

802.1p is typically not preserved across MPLS backbone without explicit mapping.

A
DSCP values can be set at the PE router to classify customer traffic into different classes.
PE routers can mark DSCP for customer traffic before entering the MPLS backbone.
B
MPLS EXP bits can be used to prioritize traffic across the service provider backbone.
EXP bits are the standard way to carry QoS across MPLS.
C
QoS policies cannot be applied to MPLS interfaces due to label encapsulation.
Why wrong: QoS policies can be applied to MPLS interfaces, often using EXP-based classification.
D
802.1p CoS marking is preserved across the MPLS backbone by default.
Why wrong: 802.1p is typically not preserved across MPLS backbone without explicit mapping.
E
Hierarchical QoS (HQoS) can be used to apply per-VPN QoS policies on a PE router.
HQoS allows separate policies for different VPNs on the same interface.

Question 8mediummultiple choice

Study all Automation and Quality of Service common traps →

Based on the exhibit, which statement is true about the QoS policy?

Exhibit

Refer to the exhibit.

class-map match-any VIDEO
 match ip dscp af41 af42 af43
!
class-map match-all VOICE
 match ip dscp ef
!
policy-map QOS-POLICY
 class VOICE
  priority percent 10
 class VIDEO
  bandwidth remaining percent 30
 class class-default
  fair-queue
!
interface GigabitEthernet0/0
 service-policy output QOS-POLICY

Trap 1: The class-default will use weighted fair queuing (WFQ).

'fair-queue' is used, which is a flow-based queuing, not CBWFQ.

Trap 2: The VIDEO class will be limited to 30% of the total interface…

'bandwidth remaining percent' provides a minimum guarantee, not a maximum limit.

Trap 3: The VIDEO class is guaranteed at least 30% of the total interface…

'bandwidth remaining percent' guarantees a percentage of the remaining bandwidth after priority, not total bandwidth.

A
The class-default will use weighted fair queuing (WFQ).
Why wrong: 'fair-queue' is used, which is a flow-based queuing, not CBWFQ.
B
The VIDEO class will be limited to 30% of the total interface bandwidth.
Why wrong: 'bandwidth remaining percent' provides a minimum guarantee, not a maximum limit.
C
The VOICE class is allocated a strict priority queue with a bandwidth limit of 10% of the interface bandwidth.
The 'priority percent 10' command provides a strict priority queue with a bandwidth limit of 10%.
D
The VIDEO class is guaranteed at least 30% of the total interface bandwidth.
Why wrong: 'bandwidth remaining percent' guarantees a percentage of the remaining bandwidth after priority, not total bandwidth.

Question 9mediummultiple choice

Study all Automation and Quality of Service common traps →

A service provider is deploying QoS on a Cisco ASR 9000 router to support a triple-play service (voice, video, data) over an Ethernet access network. The network engineer must ensure that voice traffic (EF) is prioritized, video traffic (AF41) is treated with low loss, and data traffic (default) gets best-effort service. Additionally, the engineer must implement a hierarchical QoS policy to shape the aggregate subscriber traffic to 100 Mbps on a GigabitEthernet interface, with the following per-class bandwidth allocations: voice 10 Mbps, video 40 Mbps, and data 50 Mbps. During testing, voice packets are being dropped under congestion, and video traffic is experiencing jitter. The current QoS configuration is as follows:

policy-map CHILD

class VOICE

priority level 1 police rate 10 mbps

class VIDEO

bandwidth remaining ratio 40

class DATA

bandwidth remaining ratio 50 ! policy-map PARENT

class class-default

shape average 100 mbps service-policy CHILD !

Which action should the engineer take to resolve the issues while maintaining the design objectives?

Trap 1: Change the video class to 'priority level 2' to give it…

Using a second priority level for video can still cause voice jitter and is not recommended for video.

Trap 2: Add a 'police' to the video class with a CIR of 40 Mbps and…

Video already has a bandwidth guarantee; policing video will not solve voice drops and may cause video loss.

Trap 3: Change the voice class to use 'bandwidth remaining percent 10' and…

Voice requires strict priority, not just bandwidth guarantee, to meet delay requirements.

A
Change the video class to 'priority level 2' to give it preferential treatment over data.
Why wrong: Using a second priority level for video can still cause voice jitter and is not recommended for video.
B
Remove the police from the voice class and add 'priority level 1' without police; this ensures voice is priority queued without dropping.
Priority queuing with no police allows voice packets to be transmitted ahead of other queues, avoiding drops.
C
Add a 'police' to the video class with a CIR of 40 Mbps and 'conform-action transmit exceed-action drop' to protect voice.
Why wrong: Video already has a bandwidth guarantee; policing video will not solve voice drops and may cause video loss.
D
Change the voice class to use 'bandwidth remaining percent 10' and remove the police.
Why wrong: Voice requires strict priority, not just bandwidth guarantee, to meet delay requirements.

Question 10hardmultiple choice

Study all Automation and Quality of Service common traps →

A service provider is designing a QoS policy for a multi-service MPLS VPN network that carries voice, video, and data traffic. The network uses DiffServ and MPLS EXP markings. The design must ensure that voice traffic is given priority over video and data, while video traffic should have better treatment than data but not at the expense of voice. The provider plans to use a hierarchical QoS (HQoS) policy at the PE-CE interfaces. Which configuration approach best meets these requirements?

Trap 1: Mark voice traffic with EXP 5, video with EXP 4, and data with EXP…

Marking alone does not provide queuing; the PE-CE interfaces need explicit policies.

Trap 2: Use a single-level policy with LLQ for voice and video together,…

LLQ for both voice and video could cause voice to compete with video, violating the requirement that video not affect voice.

Trap 3: Apply class-based shaping to each traffic class separately on the…

Class-based shaping does not provide priority queuing; voice could still be delayed if its queue is full.

A
Mark voice traffic with EXP 5, video with EXP 4, and data with EXP 0, and rely on the core to prioritize based on EXP.
Why wrong: Marking alone does not provide queuing; the PE-CE interfaces need explicit policies.
B
Use a single-level policy with LLQ for voice and video together, and CBWFQ for data.
Why wrong: LLQ for both voice and video could cause voice to compete with video, violating the requirement that video not affect voice.
C
Apply a parent policy with a shape for the total bandwidth and a child policy with LLQ for voice and CBWFQ for video and data.
This provides hierarchical control, ensuring voice gets priority within the shaped bandwidth while video and data get fair treatment.
D
Apply class-based shaping to each traffic class separately on the interface.
Why wrong: Class-based shaping does not provide priority queuing; voice could still be delayed if its queue is full.

Question 11mediummulti select

Study all Automation and Quality of Service common traps →

Which TWO statements accurately describe the behavior of the QoS policy shown in the exhibit?

Exhibit

Refer to the exhibit.

class-map match-any VOICE
 match ip dscp ef
class-map match-any VIDEO
 match ip dscp af41 af42
class-map match-any DATA
 match ip dscp default
!
policy-map QOS_POLICY
 class VOICE
  priority level 1
  set mpls experimental topmost 5
 class VIDEO
  bandwidth remaining percent 30
  set mpls experimental topmost 4
 class DATA
  bandwidth remaining percent 70
  set mpls experimental topmost 0
!
interface GigabitEthernet0/0/0
 service-policy output QOS_POLICY

Trap 1: The policy shapes the total output traffic to 30 Mbps.

No shaping command is present; the policy only manages queuing.

Trap 2: Video traffic is placed in a strict priority queue.

Video uses bandwidth remaining percent, not priority.

Trap 3: The policy polices voice traffic to a maximum of 30% of the…

No police command is configured; the priority queue can consume all available bandwidth.

A
The policy shapes the total output traffic to 30 Mbps.
Why wrong: No shaping command is present; the policy only manages queuing.
B
During congestion, video traffic is allocated 30% of the remaining bandwidth after voice is served.
Bandwidth remaining percent allocates a percentage of the available bandwidth after priority queues are serviced.
C
Video traffic is placed in a strict priority queue.
Why wrong: Video uses bandwidth remaining percent, not priority.
D
The policy polices voice traffic to a maximum of 30% of the interface bandwidth.
Why wrong: No police command is configured; the priority queue can consume all available bandwidth.
E
Voice traffic is guaranteed to be sent before any other traffic.
Priority level 1 ensures voice is dequeued first.

Question 12easymultiple choice

Study all Automation and Quality of Service common traps →

A service provider has deployed a new MPLS L3VPN service for a customer with multiple sites. The customer reports intermittent voice quality issues during peak hours. The provider uses a DiffServ QoS model with MPLS EXP markings. The PE routers apply the following policy on the customer-facing interfaces:

policy-map CUSTOMER-OUT

class VOICE

priority percent 10 set mpls experimental topmost 5

class VIDEO

bandwidth remaining percent 30 set mpls experimental topmost 4

class DATA

bandwidth remaining percent 70 set mpls experimental topmost 0

The core network has a simple policy that maps EXP 5 to PQ, EXP 4 to a low-latency queue, and EXP 0 to best effort. The provider monitors the network and finds that the PE-CE interfaces are not congested (average utilization is 40%), but the voice packets are experiencing jitter. The customer's voice traffic is about 5% of the link capacity. Which action is most likely to reduce the jitter?

Trap 1: Configure the core routers to map EXP 5 to a low latency queue…

Low latency queue is for video; voice should remain in PQ; the issue is at the PE-CE, not core.

Trap 2: Increase the priority percent to 20 for voice traffic.

Increasing priority does not solve jitter; it might allow voice to consume more bandwidth but does not shape it.

Trap 3: Change the set mpls experimental topmost to set ip dscp ef for…

DSCP marking is not used in the MPLS core; it does not help jitter.

A
Add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue.
Policing and shaping the priority queue prevents bursts and reduces jitter.
B
Configure the core routers to map EXP 5 to a low latency queue instead of PQ.
Why wrong: Low latency queue is for video; voice should remain in PQ; the issue is at the PE-CE, not core.
C
Increase the priority percent to 20 for voice traffic.
Why wrong: Increasing priority does not solve jitter; it might allow voice to consume more bandwidth but does not shape it.
D
Change the set mpls experimental topmost to set ip dscp ef for voice.
Why wrong: DSCP marking is not used in the MPLS core; it does not help jitter.

Question 13mediumdrag order

Study the full ACL explanation →

Drag and drop the steps to configure MPLS LDP on a Cisco router into the correct order.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 14mediumdrag order

Drag and drop the steps to configure a standard ACL on a Cisco router into the correct order.

Drag steps to the numbered slots on the right, or tap a step then tap a slot.

Steps

Order

1Step 1

2Step 2

3Step 3

4Step 4

5Step 5

Question 15mediummatching

Open the full BGP breakdown →

Match each BGP attribute to its category or purpose.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Well-known mandatory attribute for loop prevention

Well-known mandatory attribute indicating next-hop IP

Well-known discretionary attribute for best path selection

Optional non-transitive attribute to influence inbound traffic

Optional transitive attribute for route tagging and policy

Question 16mediummatching

Read the full Automation and Quality of Service explanation →

Match each network automation tool to its primary use.

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

Network configuration protocol using XML-based data encoding

Data modeling language for network device configuration and state

HTTP-based API for NETCONF data stores

Automation tool for configuration management and orchestration

High-performance RPC framework for telemetry and streaming

Question 17mediummultiple choice

Study all Automation and Quality of Service common traps →

A service provider needs to prioritize voice traffic over best-effort data in an MPLS VPN. The PE router uses a QoS policy applied to the ingress interface. Which action ensures that voice packets are marked with the correct DSCP value before entering the MPLS core?

Trap 1: Configure the ingress interface with 'mls qos trust dscp' to…

Trust is used to honor existing markings; not to set new ones.

Trap 2: Use a policy-map with the 'set mpls experimental 5' command.

This sets MPLS EXP bits, not IP DSCP.

Trap 3: Apply a police action to drop traffic exceeding the voice bandwidth.

Policing does not mark packets; it only enforces rate limits.

A
Apply a policy-map that matches voice traffic using a class-map and the 'set dscp ef' action.
Sets DSCP EF for voice packets on ingress.
B
Configure the ingress interface with 'mls qos trust dscp' to preserve the customer marking.
Why wrong: Trust is used to honor existing markings; not to set new ones.
C
Use a policy-map with the 'set mpls experimental 5' command.
Why wrong: This sets MPLS EXP bits, not IP DSCP.
D
Apply a police action to drop traffic exceeding the voice bandwidth.
Why wrong: Policing does not mark packets; it only enforces rate limits.

Open the full BGP breakdown →

Question 18easymultiple choice

A network operator deploys a QoS policy on a route reflector to classify traffic based on BGP community values. However, the policy is not matching the intended traffic. Which is the most likely cause?

Trap 1: The policy-map is applied to the wrong interface.

Interface application affects where the policy is processed, but the match condition itself is invalid.

Trap 2: The service-policy is applied in the wrong direction (input vs…

Direction affects when the policy is applied, but the match is still invalid.

Trap 3: The class-default class is consuming all traffic.

Class-default matches unclassified traffic; if a match existed it would work.

Study all Automation and Quality of Service common traps →

A
The policy-map is applied to the wrong interface.
Why wrong: Interface application affects where the policy is processed, but the match condition itself is invalid.
B
The class-map uses a match statement referencing BGP community values, which are not visible at the QoS classification stage.
BGP communities are control-plane attributes; QoS uses packet headers.
C
The service-policy is applied in the wrong direction (input vs output).
Why wrong: Direction affects when the policy is applied, but the match is still invalid.
D
The class-default class is consuming all traffic.
Why wrong: Class-default matches unclassified traffic; if a match existed it would work.

Open the full BGP breakdown →

Question 19hardmultiple choice

An SP uses BGP FlowSpec to mitigate DDoS attacks. They also want to rate-limit the traffic per FlowSpec rule. Which configuration is required to enable policing within a FlowSpec action?

Trap 1: Configure MPLS TE bandwidth reservation for the FlowSpec routes.

MPLS TE is unrelated to FlowSpec policing.

Trap 2: Use policy-based routing (PBR) to set QoS parameters.

PBR is not integrated with FlowSpec.

Trap 3: Apply a QoS policy-map to the interface and match the FlowSpec…

FlowSpec actions are defined within the BGP update, not via a separate policy-map.

Study all Automation and Quality of Service common traps →

A
Configure MPLS TE bandwidth reservation for the FlowSpec routes.
Why wrong: MPLS TE is unrelated to FlowSpec policing.
B
Use policy-based routing (PBR) to set QoS parameters.
Why wrong: PBR is not integrated with FlowSpec.
C
Apply a QoS policy-map to the interface and match the FlowSpec destination.
Why wrong: FlowSpec actions are defined within the BGP update, not via a separate policy-map.
D
Include the 'rate-limit' action in the FlowSpec rule using the 'action' clause.
FlowSpec allows rate-limiting directly in the rule definition.

Question 20mediummultiple choice

Study all Automation and Quality of Service common traps →

An SP's core router experiences excessive packet drops on a congested link. The QoS policy uses CBWFQ with 4 queues. The drops occur only in the queue for a premium business class. Which is the most likely cause?

Trap 1: The 'bandwidth remaining' command is missing from the policy-map.

That affects sharing of excess bandwidth, not dropping within a class.

Trap 2: The interface is using MLP with interleaving.

MLP interleaving is for link fragmentation and interleaving, not queue drops.

Trap 3: The queue is using tail-drop without WRED.

Tail-drop can cause drops, but the question specifies only that queue; WRED might help.

A
The 'bandwidth remaining' command is missing from the policy-map.
Why wrong: That affects sharing of excess bandwidth, not dropping within a class.
B
The interface is using MLP with interleaving.
Why wrong: MLP interleaving is for link fragmentation and interleaving, not queue drops.
C
The queue is using tail-drop without WRED.
Why wrong: Tail-drop can cause drops, but the question specifies only that queue; WRED might help.
D
The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.
Policing drops excess traffic; if the police rate is lower than the guaranteed bandwidth, drops occur.