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

Question 1

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

Accepted Answer

DSCP values can be set at the PE router to classify customer traffic into different classes.. On a PE router, DSCP values can be set or remarked to classify incoming customer traffic into distinct service classes. This classification is performed at the ingress edge of the MPLS VPN network, allowing the provider to apply appropriate per-hop behaviors (PHBs) before the traffic is label-switched.

Answer

QoS policies cannot be applied to MPLS interfaces due to label encapsulation.

Answer

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

Question 2

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

Accepted Answer

The VOICE class is allocated a strict priority queue with a bandwidth limit of 10% of the interface bandwidth.. The exhibit shows a QoS policy where the VOICE class is configured with the 'priority' command and a bandwidth statement of 10 percent. In Cisco IOS, the 'priority' command under a class map creates a strict priority queue (LLQ), and the bandwidth percentage defines the maximum amount of interface bandwidth that can be used by this queue, ensuring low-latency treatment for voice traffic. Therefore, option C is correct.

Answer

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

Answer

The VIDEO class will be limited to 30% of the total interface bandwidth.

Answer

The VIDEO class is guaranteed at least 30% of the total interface bandwidth.

Question 3

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?

Accepted Answer

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.. Hierarchical QoS (HQoS) allows the service provider to enforce a total bandwidth shape at the parent level while using a child policy to apply LLQ for voice (ensuring strict priority) and CBWFQ for video and data (ensuring video gets better treatment than data without starving voice). This meets the requirement that video should not degrade voice, as the parent shape prevents any single class from monopolizing the link, and the child policy’s LLQ guarantees voice priority over all other traffic.

Answer

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.

Answer

Use a single-level policy with LLQ for voice and video together, and CBWFQ for data.

Answer

Apply class-based shaping to each traffic class separately on the interface.

Question 4

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

Accepted Answer

During congestion, video traffic is allocated 30% of the remaining bandwidth after voice is served.. The policy uses the 'bandwidth remaining percent' command under the video class, which allocates 30% of the remaining bandwidth after the voice class (which is in a strict priority queue) has been served. This is the standard behavior for class-based weighted fair queuing (CBWFQ) when a priority queue is present: the priority traffic is serviced first, and then the remaining bandwidth is distributed according to the 'bandwidth remaining percent' values assigned to the non-priority classes.

Answer

The policy shapes the total output traffic to 30 Mbps.

Answer

Video traffic is placed in a strict priority queue.

Answer

The policy polices voice traffic to a maximum of 30% of the interface bandwidth.

Question 5

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

Accepted Answer

Enter global configuration mode, then create the standard access list, then enter interface configuration mode, then apply the access list to the interface.. Standard ACL configuration requires creating the ACL and applying it to an interface in the appropriate direction.

Answer

Enter global configuration mode, then enter interface configuration mode, then create the standard access list, then apply the access list to the interface.

Answer

Create the standard access list, then enter global configuration mode, then enter interface configuration mode, then apply the access list to the interface.

Answer

Enter global configuration mode, then create the standard access list, then apply the access list to the interface, then enter interface configuration mode.

Question 6

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?

Accepted Answer

Apply a policy-map that matches voice traffic using a class-map and the 'set dscp ef' action.. The question specifies that the PE router must mark voice packets with the correct DSCP value before they enter the MPLS core. The 'set dscp ef' action in a policy-map applied to the ingress interface explicitly sets the DSCP field to EF (46) for voice traffic matched by a class-map, ensuring proper classification and treatment across the MPLS network. This is the standard method for marking IP packets at the edge before MPLS encapsulation.

Answer

Configure the ingress interface with 'mls qos trust dscp' to preserve the customer marking.

Answer

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

Answer

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

Question 7

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?

Accepted Answer

The class-map uses a match statement referencing BGP community values, which are not visible at the QoS classification stage.. BGP community values are exchanged as part of the BGP routing update and are stored in the BGP table, but they are not carried in the IP packet header. QoS classification in Cisco IOS operates on fields within the Layer 2 or Layer 3 packet header (e.g., DSCP, IP precedence, CoS) and cannot inspect BGP attributes like community values. Therefore, a class-map using a match statement for BGP communities will never match traffic at the QoS classification stage, making this the most likely cause of the policy not working.

Answer

The policy-map is applied to the wrong interface.

Answer

The service-policy is applied in the wrong direction (input vs output).

Answer

The class-default class is consuming all traffic.

Question 8

A SP wants to automate the deployment of QoS policies on numerous PE routers using NETCONF. Which YANG module is most appropriate for modeling the QoS policy-map configuration?

Accepted Answer

Cisco-IOS-XR-qos-ma-cfg. The Cisco-IOS-XR-qos-ma-cfg YANG module is specifically designed to model QoS policy-map configurations on Cisco IOS XR platforms. Since the SP is using NETCONF to automate QoS policies on PE routers running IOS XR, this native module provides the exact data model for defining class-maps, policy-maps, and service policies, aligning with the task's requirement.

Answer

ietf-interfaces

Answer

Cisco-IOS-XR-ip-tcp-yang

Answer

ietf-netconf-acm

Question 9

An SP engineer implements LLQ for VoIP traffic on a DS3 link. The policy-map calls for a priority queue of 500 kbps. The actual VoIP traffic averages 400 kbps with bursts to 600 kbps. What is the expected behavior during bursts?

Accepted Answer

The priority queue drops all traffic above the configured 500 kbps during the burst.. C is correct because the priority queue in a Low Latency Queueing (LLQ) policy is policed at the configured rate (500 kbps). When VoIP traffic bursts exceed this rate, the excess packets are dropped immediately by the policer, not queued or reclassified. This ensures that the priority queue does not starve other queues and maintains low latency for conforming traffic.

Answer

The excess traffic is reclassified to best-effort and placed in the default queue.

Answer

The priority queue uses tail-drop and discards only when the queue is full.

Answer

The excess traffic is queued in the priority queue until bandwidth is available.

Question 10

An SP router is configured with a hierarchical QoS policy (parent policy shaper, child policy with CBWFQ). When applying this policy to an interface, the router reports 'Policy map not found' error. What is the most likely cause?

Accepted Answer

The child policy-map specified in the parent's 'service-policy' command does not exist.. The 'Policy map not found' error occurs when the parent policy-map references a child policy-map via the 'service-policy' command, but that child policy-map does not exist in the router's configuration. Hierarchical QoS requires both the parent and child policy-maps to be created and correctly named; a missing child policy-map prevents the router from applying the nested policy.

Answer

The interface speed is not configured.

Answer

The interface is not part of a bridge domain.

Answer

The shape average command in the parent policy uses an unsupported value.

Question 11

Which TWO statements about model-driven telemetry compared to SNMP are correct? (Choose two.)

Accepted Answer

Model-driven telemetry can stream data at sub-second intervals.. Model-driven telemetry (MDT) uses a push model where the network device streams structured data (e.g., YANG-modeled) to a collector, enabling sub-second intervals for real-time monitoring. This contrasts with SNMP's pull model, where the manager polls the device at intervals limited by CPU and network overhead, making sub-second polling impractical.

Answer

Model-driven telemetry uses UDP for transport by default.

Answer

Model-driven telemetry only sends data on change (event-driven).

Answer

Model-driven telemetry uses MIBs to define data structures.

Question 12

Which THREE YANG data nodes are part of the Cisco-IOS-XR-qos-ma-cfg module for defining a QoS policy-map? (Choose three.)

Accepted Answer

class. The 'class' YANG data node is defined in the Cisco-IOS-XR-qos-ma-cfg module to specify a traffic class within a QoS policy-map. This node allows you to associate a class-map with the policy, enabling differentiated treatment of traffic based on classification criteria.

Answer

urn:cisco:params:xml:ns:yang:Cisco-IOS-XR-qos-ma-cfg

Answer

interface

Question 13

Which TWO are valid benefits of automating QoS policy management in a large SP network? (Choose two.)

Accepted Answer

Reduced human error in configuration.. Automating QoS policy management eliminates manual configuration steps, reducing the risk of syntax errors, misapplied policies, or inconsistent deployments across thousands of devices. Automation tools like Ansible or NSO enforce standardized templates and pre-validated configurations, directly lowering human error rates in large SP networks.

Answer

Eliminates the need for monitoring QoS performance.

Answer

Slower deployment of QoS changes.

Answer

Requires no validation of configurations before apply.

Question 14

Which THREE are common causes of QoS misconfiguration on PE routers? (Choose three.)

Accepted Answer

Applying a policy-map in the wrong direction (input vs output).. Applying a policy-map in the wrong direction (input vs output) is a common QoS misconfiguration because QoS actions like shaping, policing, and queuing are direction-specific. For example, shaping is typically applied on the egress interface to control outbound traffic, while policing can be applied inbound to rate-limit incoming traffic. Misapplying a policy-map (e.g., attaching a shaper to the input direction) will either be ignored by the router or cause unexpected behavior, leading to QoS failures.

Answer

Using the 'bandwidth percent' command in a class that also has a priority queue.

Answer

Insufficient bandwidth on the subscriber line.

Question 15

Refer to the exhibit. An engineer applies two service policies to the same subinterface in the outbound direction. Which statement describes the expected behavior?

Accepted Answer

Only the SHAKE-1M policy is applied; the CHILD-QOS policy is ignored.. When two service policies are applied to the same subinterface in the same direction, the router only honors the first policy applied; the second policy is ignored. In this case, SHAKE-1M was applied first, so CHILD-QOS is not processed. Cisco IOS does not allow multiple service policies in the same direction on a single interface or subinterface, as each direction can have only one active policy-map.

Answer

The router automatically nests CHILD-QOS inside SHAKE-1M creating hierarchical QoS.

Answer

The router compiles a combined policy that merges classifications.

Answer

Both policies are applied sequentially; traffic is shaped then classified.