350-501 Automation and Quality of Service Practice Test 3 — 15 Questions

Question 1

Refer to the exhibit. A network automation engineer uses NETCONF to retrieve the QoS policy 'POLICE-CUSTOMER'. Based on the response, what is the effect of this policy?

Accepted Answer

It polices all traffic to a maximum of 256 kbps and drops excess.. The NETCONF response shows a 'police' configuration under the QoS policy 'POLICE-CUSTOMER' with a committed information rate (CIR) of 256000 bps (256 kbps) and a conform-action of 'transmit' with an exceed-action of 'drop'. This is a standard policing action that meters traffic to the specified rate and drops any packets that exceed it, as defined in RFC 2697 (Single Rate Three Color Marker). Option A correctly identifies this behavior.

Answer

It sets DSCP CS4 on traffic exceeding 256 kbps.

Answer

It guarantees a priority queue for traffic up to 256 kbps.

Answer

It shapes traffic to an average rate of 256 kbps.

Question 2

Refer to the exhibit. An engineer monitors the queue depths on a core interface. Which class is experiencing the most congestion?

Accepted Answer

Best-effort class, because its average depth is 580.. The exhibit shows that the best-effort class has an average queue depth of 580 packets, which is significantly higher than the voice class's average depth. This indicates that the best-effort class is experiencing the most congestion, as queue depth is a direct measure of buffered packets waiting for transmission. The voice class, despite having a taildrop threshold, has a much lower average depth, showing it is not as congested.

Answer

The interface is not congested because bandwidth is 1 Gbps.

Answer

Voice class, because it has a taildrop threshold.

Answer

Both classes equally, because they both have taildropping.

Question 3

A network engineer notices that voice traffic is being dropped during congestion. The traffic is marked with DSCP EF. After reviewing the QoS policy, it is discovered that the voice traffic is not being placed into a priority queue. Which configuration change would ensure voice traffic receives priority treatment?

Accepted Answer

Add the 'priority' command under the voice class in the policy map. DSCP EF (Expedited Forwarding, per RFC 3246) requires strict priority queuing to guarantee low latency and jitter for voice traffic. The 'priority' command under the voice class in a policy map places the traffic into a strict priority queue (LLQ), ensuring it is serviced before any other queue during congestion. Without this command, the voice traffic is treated as a regular class, subject to bandwidth constraints and potential drops.

Answer

Increase the queue limit to 1000 packets

Answer

Increase the bandwidth percentage for the voice class

Answer

Enable WRED on the voice class

Question 4

A service provider uses a centralized automation system to manage QoS policies via NETCONF and YANG. When attempting to push a new policy-map, the device returns an error indicating that the policy-map type is not supported in the specified location. What is the most likely cause?

Accepted Answer

The policy-map is being applied to an interface that does not support hierarchical QoS. The error indicates that the policy-map type is not supported in the specified location. This typically occurs when a policy-map is applied to an interface that does not support hierarchical QoS (HQoS), such as a physical interface that requires a service-policy under a parent policy-map. The NETCONF/YANG operation succeeds in syntax but fails due to device-level capability constraints.

Answer

The YANG module for QoS is not installed on the device

Answer

The NETCONF session is not authenticated

Answer

The automation system is using the wrong namespace

Question 5

While troubleshooting a customer complaint about slow data transfers, you notice that traffic from a specific site is being dropped. The QoS policy on the PE router includes a police command for the customer's traffic. The observed drop rate is exactly half of the configured police rate. What is the most probable reason?

Accepted Answer

The police is using a token-bucket algorithm with a small burst size that is being exceeded. The observed drop rate being exactly half the configured police rate strongly suggests that the token-bucket algorithm is operating with a burst size that is too small. When the burst size is insufficient, the bucket empties quickly under sustained traffic, causing packets to be marked as exceeding the rate and dropped. The police command in Cisco IOS uses a single-rate two-color marker (RFC 2697) or a two-rate three-color marker (RFC 2698), and a small burst size leads to premature drops even when the average rate is below the configured police rate.

Answer

The police rate is configured in bits per second but the traffic is measured in bytes per second

Answer

The traffic is using a different DSCP value than expected

Answer

The police action is set to drop, but the exceed-action is transmit

Question 6

A network administrator needs to automate the deployment of a new QoS policy on dozens of provider edge routers. Which Cisco tool is best suited for this purpose?

Accepted Answer

Cisco Network Services Orchestrator (NSO). Cisco Network Services Orchestrator (NSO) is the correct tool because it provides model-driven orchestration and automation for deploying and managing network configurations across hundreds of devices using YANG data models and NETCONF. For QoS policy deployment, NSO can push consistent service definitions (e.g., class-maps, policy-maps, service-policy) to multiple provider edge routers simultaneously, ensuring compliance and reducing manual errors.

Answer

Cisco SecureX

Answer

Cisco Prime Infrastructure

Answer

Cisco ISE

Question 7

An engineer is using NETCONF to retrieve the operational QoS statistics from a router. The response contains XML data but does not include the queueing statistics. What is the most likely reason?

Accepted Answer

The NETCONF filter did not include the correct YANG path for QoS statistics. NETCONF retrieves data based on YANG models. If the filter does not specify the correct YANG path for QoS queueing statistics, the server will not include that data in the response. The YANG data model for QoS (e.g., Cisco‑IOS‑XE‑qos‑oper.yang) defines specific paths for queueing counters; omitting or mis‑specifying the filter path results in an incomplete reply.

Answer

The user does not have enough privilege level

Answer

The statistics are only available via SNMP

Answer

The router is running an older IOS that does not support NETCONF

Question 8

During a maintenance window, an automation script pushed a QoS policy that inadvertently changed the marking for all inbound traffic on a core interface. The change was rolled back, but performance reports show that some traffic is still being marked incorrectly. What is the most logical explanation?

Accepted Answer

The rolled back policy was applied inbound, but the outbound policy that also applies marking was not rolled back. QoS policies can be applied independently in the inbound and outbound directions on an interface. If the original automation script modified the inbound marking policy, and the rollback only reverted that inbound policy, any outbound policy that also performs marking would remain unchanged and continue to incorrectly mark traffic. This explains why some traffic still shows incorrect marking after the rollback.

Answer

The automation script used RESTCONF which requires a commit to finalize

Answer

The device requires a reload to clear the old marking

Answer

The rollback script only applied to the outbound direction

Question 9

An SP engineer is configuring QoS on a router and needs to drop traffic that exceeds a certain rate while allowing bursts up to a specified amount. Which QoS feature should be used?

Accepted Answer

Policing. Policing is the correct QoS feature because it drops traffic that exceeds a configured rate while allowing bursts up to a specified amount. Unlike shaping, which buffers excess traffic, policing enforces a rate limit by immediately dropping or re-marking packets that exceed the configured committed information rate (CIR) and burst size (Bc/Be). This matches the requirement to drop traffic that exceeds a certain rate while permitting bursts.

Answer

Shaping

Answer

WRED

Answer

Queueing

Question 10

A customer is using a Cisco ASR 9000 router with hierarchical QoS (HQoS) on a subscriber interface. The parent policy sets a shape rate of 10 Mbps, but the observed traffic rate is only 8 Mbps. What is a common misconfiguration that would cause this?

Accepted Answer

The child policy includes a police command that is limiting traffic below the parent shaper rate. In hierarchical QoS (HQoS) on a Cisco ASR 9000, the parent policy shapes traffic to a specified rate, but if the child policy includes a police command, that policer can independently drop or mark down traffic before it reaches the parent shaper. This causes the observed traffic rate to be lower than the parent shape rate, as the child policer is the actual bottleneck. The correct answer is A because the police command in the child policy is limiting traffic below the 10 Mbps parent shaper, resulting in only 8 Mbps observed.

Answer

The child policy uses 'bandwidth remaining' instead of 'bandwidth'

Answer

The child policy includes a bandwidth command that exceeds the parent shaper rate

Answer

The parent shaper uses 'shape peak' instead of 'shape average'

Question 11

An automation engineer is writing a Python script using Cisco's pyATS library to validate QoS configurations across a fleet of routers. The script runs without errors but reports that all routers are compliant even though some are not. What is the most likely issue?

Accepted Answer

The script uses a single 'show running-config' without filtering, and the parser fails to locate QoS policies applied under interfaces. The pyATS parser for 'show running-config' without filtering may not recursively parse QoS policy-map configurations applied under interfaces. When the script uses a single unfiltered 'show running-config', the parser might fail to extract QoS policies nested under interface sub-configurations, leading to false compliance reports. This is a common issue where the parser's data model does not map deeply nested CLI structures like 'service-policy input/output' under interfaces.

Answer

The pyATS library does not support QoS features for the specific platform

Answer

The testbed credentials are incorrect but the script still returns compliant

Answer

The script is parsing the startup-config instead of running-config

Question 12

A network engineer is implementing QoS on a Cisco ASR 1000 for a customer with multiple service classes. The customer requires that mission-critical data not be starved when voice traffic bursts. Which two actions should the engineer take? (Choose two.)

Accepted Answer

Configure a policer on the voice class to limit its bandwidth. Policing the voice class limits its bandwidth to a configured rate (e.g., using the `police` command under the class-map), preventing voice bursts from starving mission-critical data. This ensures that voice traffic does not exceed its allocated share, leaving enough bandwidth for other classes. Option D is correct because allocating a minimum bandwidth guarantee to the data class (e.g., using the `bandwidth` command under the class-map) ensures that even when voice bursts occur, the data class receives a reserved amount of bandwidth, preventing starvation. Together, these actions enforce admission control and bandwidth reservation, aligning with the customer's requirement.

Answer

Enable WRED on the voice class

Answer

Use tail drop with a high threshold for the data class

Answer

Configure a shape on the voice class to 75% of interface bandwidth

Question 13

A service provider is automating QoS policy deployment using Cisco NSO and YANG. During validation, the engineer discovers that the pushed policy is not taking effect. Which three possible causes should be investigated? (Choose three.)

Accepted Answer

The device does not support the YANG model used. Cisco NSO uses YANG models to translate service definitions into device-specific CLI or NETCONF operations. If the target device does not support the YANG model referenced in the service package, the NETCONF or CLI operations will fail silently or produce no effect, as the device cannot interpret the configuration intent. This is a common validation failure when using model-driven orchestration with heterogeneous device populations.

Answer

The device has a feature license missing for QoS

Answer

The policy-map name conflicts with an existing one

Question 14

During QoS troubleshooting, you capture traffic and see that DSCP markings are not being applied as configured. Which two common misconfigurations could cause this? (Choose two.)

Accepted Answer

The policy-map is not applied to the correct interface direction (input vs output). A policy-map must be applied in the correct direction (input or output) for the marking to take effect. If a marking policy is applied to the wrong direction, the packets will not be processed by the policy, and DSCP values will remain unchanged. This is a common misconfiguration when the intended marking should occur on ingress but the policy is applied to egress, or vice versa.

Answer

The policy-map is applied to a loopback interface

Answer

The marking is configured under the wrong policy-map

Answer

The device is running out of TCAM space

Question 15

Refer to the exhibit. The policy above is applied on a PE router. The customer complains that voice quality is poor. Based on the exhibit, what is the most likely cause?

Accepted Answer

The police rate for voice is too low for the offered traffic. The police rate for voice is too low for the offered traffic. Voice traffic requires a guaranteed bandwidth to maintain low jitter and packet loss; if the policer rate is set below the actual voice flow rate, packets are dropped or marked down, causing poor voice quality. In the exhibit, the voice class has a police rate that is insufficient for the offered load, leading to excessive drops.

Answer

The policy is applied to the wrong direction

Answer

The class-default is empty

Answer

The DATA class is not matching any traffic