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

Question 1

An SP uses NSO with a YANG service model to provision an L3VPN. The service model references a leafref to a VPN ID that must exist in a separate list. Which YANG statement ensures the leafref value is valid against the referenced list?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

type leafref { path '/vpn-list/vpn-id'; }. leafref automatically validates that the leaf value matches a leaf in the referenced path.

Answer

must 'current() = /vpn-list/vpn-id';

Answer

mandatory true;

Answer

type string { pattern '[0-9]+'; }

Question 2

Which MQC component is used to match traffic based on criteria such as DSCP or IP precedence?

Accepted Answer

Class-map. In the Modular QoS CLI (MQC), the class-map component is used to define traffic classes by matching packets based on criteria such as DSCP (Differentiated Services Code Point) or IP precedence values. The class-map uses match statements (e.g., match ip dscp, match ip precedence) to classify traffic, which is then applied within a policy-map for QoS actions. This makes class-map the correct MQC component for traffic matching.

Answer

Service-policy

Answer

Policy-map

Answer

Access-list

Question 3

An SP router is configured with CBWFQ. For a data class requiring 30% bandwidth guarantee, which command is correct in the policy-map?

Accepted Answer

bandwidth percent 30. The 'bandwidth percent' command allocates a percentage of the interface bandwidth to the class.

Answer

fair-queue

Answer

priority percent 30

Answer

bandwidth 30

Question 4

When automating service provisioning with NSO, which three components are part of the NSO architecture? (Choose three.)

Accepted Answer

YANG service model. The YANG service model is a core component of NSO architecture. It defines the service logic and data model that translates high-level service requests into device-specific configurations. NSO uses YANG to model both services and devices, enabling automation of service provisioning.

Answer

Java API

Answer

SNMP

Question 5

Which DSCP value is recommended for Expedited Forwarding (EF) per-hop behavior, commonly used for voice traffic?

Accepted Answer

DSCP 46. Expedited Forwarding (EF) per-hop behavior is defined in RFC 3246 and is designed for low-loss, low-latency, and low-jitter services such as voice traffic. The recommended DSCP value for EF is 46 (binary 101110), which corresponds to the PHB that ensures a dedicated forwarding treatment with a minimal queueing delay. This value is widely adopted in Cisco QoS deployments for voice payloads to guarantee strict priority queuing.

Answer

DSCP 10

Answer

DSCP 0

Answer

DSCP 34

Question 6

A service provider wants to enforce a hard rate limit of 10 Mbps on a subscriber's traffic, dropping any excess packets. Which QoS mechanism should be used?

Accepted Answer

Policing. Policing drops or re-marks traffic exceeding the configured rate, enforcing a hard limit. Shaping buffers excess traffic, which does not enforce a hard drop.

Answer

CBWFQ

Answer

Traffic shaping

Answer

LLQ

Question 7

In an SP network using NSO for service orchestration, which component abstracts device-specific CLI or SNMP interactions into a common model for NETCONF/RESTCONF southbound communication?

Accepted Answer

NED (Network Element Driver). The Network Element Driver (NED) provides the abstraction layer between NSO and network devices, translating YANG models to device-specific configurations (e.g., CLI, SNMP).

Answer

YANG model

Answer

CDB (Configuration Database)

Answer

RESTCONF northbound API

Question 8

Which NETCONF RPC is used to retrieve the complete running configuration from a network device?

Accepted Answer

get-config. get-config with running retrieves the running configuration. The RPC retrieves both configuration and state data.

Answer

edit-config

Answer

get

Answer

lock

Question 9

A service provider is implementing hierarchical QoS on an edge router. The goal is to shape the aggregate traffic to 100 Mbps and then apply different queuing policies for voice and data within that shaped pipe. Which configuration approach is correct?

Accepted Answer

Configure a parent policy-map with shape and a child policy-map with queuing, then apply the child under the parent's class.. Hierarchical QoS in Cisco IOS uses a nested policy-map structure: the parent policy-map contains the shaping action (e.g., shape average 100000000) and references a child policy-map via the 'service-policy' command inside the class. The child policy-map contains the queuing actions (e.g., priority for voice, bandwidth for data). This creates a shaper with a nested queuing hierarchy, which is the correct way to shape aggregate traffic and then queue within the shaped pipe.

Answer

Apply shaping on the interface and queuing on a subinterface separate from the policy-map.

Answer

Use a child policy-map for shaping and a parent policy-map for queuing.

Answer

Apply a single policy-map with both shape and queue commands under the same class.

Question 10

In the MQC (Modular QoS CLI) framework, which component is used to match traffic based on DSCP values?

Accepted Answer

Class-map. Class-maps define match criteria (e.g., match ip dscp 46) to classify traffic in MQC.

Answer

Service-policy

Answer

Access-list

Answer

Policy-map

Question 11

An SP network operator needs to ensure that voice traffic always gets priority access to the output link. Which queuing mechanism is designed to provide a strict priority queue while preventing starvation of other queues?

Accepted Answer

LLQ. LLQ provides a strict priority queue for EF traffic and includes a policer to limit the priority traffic rate, preventing starvation of other queues.

Answer

CBWFQ

Answer

FIFO

Answer

WRED

Question 12

In SR-PCE architecture, which protocol is used for communication between the Path Computation Element (PCE) and the Path Computation Client (PCC) to request and report SR-TE paths?

Accepted Answer

PCEP. B is correct because the Path Computation Element Protocol (PCEP), defined in RFC 5440 and extended for Segment Routing in RFC 8664, is the dedicated protocol used between a PCE and a PCC to request, report, and delegate SR-TE paths. PCEP carries explicit path computation requests (PCReq) and replies (PCRep), as well as state reporting (PCRpt) and delegation (PCUpd) messages, making it the standard control-plane protocol for SR-PCE architectures.

Answer

RESTCONF

Answer

NETCONF

Answer

BGP-LS

Question 13

When DSCP markings are mapped to MPLS EXP bits at the ingress PE router, how many EXP values are available for traffic differentiation in the MPLS core?

Accepted Answer

8. MPLS EXP (now TC) is a 3-bit field, providing 8 possible values (0-7).

Answer

16

Answer

64

Answer

32

Question 14

A service provider is designing a QoS policy for a business VPN service that carries voice, video, and data. The policy must ensure that voice (EF) is never dropped even during congestion, while video (AF41) and data (AF21) share the remaining bandwidth in a ratio 2:1. Which queuing strategy should be used?

Accepted Answer

Apply LLQ for voice and CBWFQ for video and data with bandwidth ratio 2:1.. LLQ provides strict priority queuing for voice (EF), ensuring it is never dropped during congestion, while CBWFQ allows the remaining bandwidth to be shared among video (AF41) and data (AF21) in a 2:1 ratio. LLQ is designed to guarantee low latency for real-time traffic, and CBWFQ enables explicit bandwidth allocation for non-real-time classes. This combination meets the requirement of zero-drop for voice and proportional sharing for video and data.

Answer

Use only LLQ for all three classes.

Answer

Apply CBWFQ with bandwidth percentages to all three classes.

Answer

Use FIFO queuing with WRED for all classes.

Question 15

In NSO, which statement best describes the function of the CDB (Configuration Database)?

Accepted Answer

It holds the configuration and operational data of managed devices, acting as a centralized datastore.. The CDB (Configuration Database) in Cisco NSO is the central datastore that holds both configuration and operational data for all managed devices. It acts as a single source of truth, storing the intended configuration and the actual state retrieved from devices. This enables NSO to provide a network-wide view and to perform transactions, rollbacks, and reconciliation.

Answer

It translates NETCONF RPCs to device-specific CLI commands.

Answer

It stores YANG models for service definition.

Answer

It provides a northbound API for OSS/BSS integration.