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

Question 1

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 2

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 3

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 4

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 5

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 uses a parent policy for shaping and a child policy for classification and queuing. The parent policy applies shape, and the child policy is attached to a class within the parent.

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 6

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 7

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 8

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 9

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 10

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 11

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.. CDB stores the intended configuration and operational state for managed devices, enabling NSO to compare and sync with actual device configurations.

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.

Question 12

Which congestion avoidance mechanism is used to prevent tail drop by selectively dropping packets from lower-priority flows before the queue becomes full?

Accepted Answer

WRED. WRED (Weighted Random Early Detection) drops packets probabilistically based on queue depth and IP precedence/DSCP, avoiding synchronization and providing congestion avoidance.

Answer

Policing

Answer

LLQ

Answer

CBWFQ

Question 13

A service provider wants to use NETCONF to manage devices. Which two statements are true about NETCONF operations? (Choose two.)

Accepted Answer

edit-config is used to modify configuration datastores.. NETCONF uses RPCs like get-config and edit-config; it runs over SSH (RFC 6242) and uses XML encoding.

Answer

get retrieves only operational state data.

Answer

NETCONF uses HTTP methods like POST and GET.

Answer

NETCONF uses JSON encoding by default.

Question 14

Which three mechanisms are used within the DiffServ model to provide QoS in an SP network? (Choose three.)

Accepted Answer

Classification and marking at the edge using DSCP. In the DiffServ model, QoS is implemented by classifying and marking packets at the network edge using the DSCP field in the IP header. This marking determines how each packet is treated within the core network, enabling scalable, class-based service differentiation without per-flow state.

Answer

End-to-end path computation via PCEP

Answer

IntServ resource reservation via RSVP

Question 15

An SP engineer is configuring a policy-map to implement hierarchical QoS. Which two statements are correct when using MQC for hierarchical QoS? (Choose two.)

Accepted Answer

The child policy-map must include the bandwidth and priority commands to define queuing behavior.. In hierarchical QoS using MQC, the child policy-map must include bandwidth/priority commands to define queuing behavior (B). The parent policy-map contains the shape command and references a child policy-map (C). The service-policy command is applied directly to the interface, referencing the parent policy (D). Therefore, options B, C, and D are correct. Note: The question stem asks for two, but all three are accurate statements.

Answer

Hierarchical QoS supports only two levels of nesting.

Answer

Both shape and priority commands must be configured in the same policy-map.