350-501 Automation and Quality of Service Practice Test 2 — 15 Questions

Question 1

Match each BGP attribute to its category or purpose.

Accepted Answer

Local Preference: Well-known discretionary attribute used for outbound traffic influence. Correct matches associate BGP attributes with their standard categories and purposes. Local Preference and Next Hop are well-known discretionary and mandatory respectively, while MED is optional nontransitive. Common confusions include misclassifying attribute categories or purposes.

Answer

Local Preference: Optional transitive attribute used to tag routes

Answer

AS Path: Optional nontransitive attribute used for inbound traffic influence

Question 2

Match each network automation tool to its primary use.

Accepted Answer

Ansible: An agentless automation tool that uses YAML playbooks for configuration management and application deployment.. These are key automation and programmability tools for service provider networks.

Answer

Ansible: A configuration management tool that uses a declarative language and a client-server model.

Answer

Puppet: A tool that uses YAML playbooks for automation.

Question 3

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 4

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 5

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?

Accepted Answer

Include the 'rate-limit' action in the FlowSpec rule using the 'action' clause.. BGP FlowSpec allows the inclusion of a 'rate-limit' action within the FlowSpec rule's 'action' clause to enforce policing. This action directly applies a traffic rate limit (in bits per second) to the matched flow, enabling DDoS mitigation without requiring external QoS policies or MPLS TE reservations.

Answer

Configure MPLS TE bandwidth reservation for the FlowSpec routes.

Answer

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

Answer

Apply a QoS policy-map to the interface and match the FlowSpec destination.

Question 6

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?

Accepted Answer

The premium class is configured with a police action that drops traffic when it exceeds the committed information rate.. The premium business class queue is experiencing excessive packet drops because a police action configured with a 'drop' exceed-action is discarding traffic that exceeds the committed information rate (CIR). Unlike congestion management (queuing), policing is a congestion avoidance mechanism that drops packets immediately when the traffic rate surpasses the configured CIR, regardless of the queue depth or available bandwidth. This explains why drops occur only in the premium class queue, as the policer is explicitly dropping excess packets before they even enter the CBWFQ scheduler.

Answer

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

Answer

The interface is using MLP with interleaving.

Answer

The queue is using tail-drop without WRED.

Question 7

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 8

An SP uses model-driven telemetry to monitor queue depths on core interfaces. They observe periodic spikes in the queue depth for EF traffic, causing increased latency. Which automation technique could dynamically adjust the QoS policy to mitigate the spikes?

Accepted Answer

Use a Python script that consumes telemetry data and adjusts the EF bandwith percentage via NETCONF when queue depth exceeds a threshold.. It combines model-driven telemetry (to detect queue depth spikes in real time) with a closed-loop automation approach: a Python script consumes the telemetry data, and when the EF queue depth exceeds a threshold, it dynamically adjusts the EF bandwidth percentage via NETCONF. This directly addresses the periodic spikes by modifying the QoS policy on the fly, reducing latency without manual intervention.

Answer

Deploy NETCONF YANG modules for VRF configuration.

Answer

Configure WRED on the EF queue.

Answer

Implement streaming telemetry to collect data every 5 seconds.

Question 9

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 10

An SP engineer configures a QoS policy on an IOS XR router to re-mark DSCP from AF11 to AF22 for traffic matching a specific ACL. The policy compiles successfully but traffic is not re-marked. What is a likely reason?

Accepted Answer

The interface does not have the 'qos' feature enabled, or the policy-map is not attached.. On IOS XR routers, QoS policies require explicit feature enablement via the 'qos' command under the interface configuration, and the policy-map must be attached in the correct direction. Without the 'qos' feature enabled, the router will compile the policy but silently ignore it, resulting in no re-marking of DSCP from AF11 to AF22.

Answer

The ACL cannot match on DSCP values.

Answer

The ACL is applied to the wrong interface.

Answer

The policy is applied in the output direction; marking can only be done on ingress.

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.