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

Question 1

A service provider is deploying a QoS policy for a customer with voice, mission-critical data, and best-effort traffic. The voice requires strict priority and low latency. Which queuing mechanism should be used to ensure voice packets are always served before other queues, and what additional measure is necessary to prevent voice traffic from starving other traffic?

Accepted Answer

LLQ for voice; policing on the priority queue to limit voice traffic to a configured rate.. LLQ provides a strict priority queue for delay-sensitive traffic like voice. However, to prevent starvation of other traffic, policing must be applied to the priority queue to limit the amount of voice traffic allowed into it.

Answer

FIFO queuing with a priority list; no policing needed because FIFO handles voice adequately.

Answer

CBWFQ with bandwidth percent for voice; no additional measure needed because CBWFQ inherently prevents starvation.

Answer

WRED for voice; tail drop for data; this ensures low latency for voice.

Question 2

In the DiffServ model, which DSCP value is used for Voice over IP (VoIP) traffic to ensure Expedited Forwarding (EF) per-hop behavior?

Accepted Answer

DSCP 46 (EF). EF PHB is used for low-loss, low-latency traffic such as voice. The recommended DSCP value for EF is 46 (binary 101110).

Answer

DSCP 34 (AF41)

Answer

DSCP 26 (AF31)

Answer

DSCP 0 (Best Effort)

Question 3

An SP network engineer needs to implement hierarchical QoS on a PE router to shape customer traffic to a contracted rate of 10 Mbps while providing priority for voice traffic and bandwidth guarantee for critical data. Which MQC configuration correctly achieves this?

Accepted Answer

Create a child policy with class-maps for voice and data; create a parent policy that applies the child policy and shapes to 10 Mbps; apply parent policy to the interface.. Hierarchical QoS (HQoS) is required when you need to shape traffic to a contracted rate (e.g., 10 Mbps) while also applying per-class actions like priority and bandwidth guarantees. Option A correctly uses a child policy to define class-based QoS (priority for voice, bandwidth for critical data) and a parent policy that applies the shape average command to the entire child policy aggregate, enforcing the 10 Mbps contract. This two-level MQC structure ensures that shaping occurs at the parent level before the child policy’s per-class queuing and scheduling are applied.

Answer

Apply a service-policy out with shape and then apply another service-policy in with priority; both on the same interface.

Answer

Apply a single policy-map that includes both shape and priority; no hierarchy needed.

Answer

Use a policy-map with shape average 10 Mbps and then use the bandwidth command for voice and data classes; no hierarchy.

Question 4

In SP automation, which protocol is used by NSO to communicate with network devices for configuration management?

Accepted Answer

NETCONF. NSO uses NETCONF as the southbound protocol to communicate with devices. NETCONF provides transactional configuration operations like edit-config and get-config.

Answer

RESTCONF

Answer

SNMP

Answer

CLI

Question 5

An SP uses traffic policing and shaping to manage bandwidth. Which statement best describes the difference between the two mechanisms?

Accepted Answer

Shaping buffers excess traffic to smooth bursts, while policing drops or re-marks excess traffic.. Shaping buffers excess packets to smooth traffic and reduce bursts, while policing drops or re-marks excess packets to enforce a strict rate limit.

Answer

Both mechanisms buffer excess traffic but policing uses a smaller buffer.

Answer

Shaping drops excess traffic while policing buffers it.

Answer

Policing buffers excess traffic while shaping drops it.

Question 6

In the context of MPLS QoS, at which point are EXP bits typically set based on the DSCP value of the IP packet?

Accepted Answer

At the ingress PE router before the packet enters the MPLS core.. In MPLS QoS, the EXP bits are set at the ingress PE router because this is where the IP packet first encounters the MPLS domain. The ingress PE maps the incoming IP packet's DSCP value to the MPLS EXP bits using a configured trust boundary or marking policy (e.g., 'policy-map' with 'set mpls experimental imposition'). This ensures that the QoS treatment is applied consistently across the MPLS core, as P routers typically forward based on the EXP bits without inspecting the original IP header.

Answer

At the P routers in the core based on routing protocols.

Answer

At the egress PE router when packets are forwarded to the CE.

Answer

At the CE router before sending to the PE.

Question 7

An SP uses SR-PCE for traffic engineering. Which protocol does the SR-PCE use to communicate path computation requests and responses with path computation clients (PCCs)?

Accepted Answer

PCEP. PCEP (Path Computation Element Protocol) is used between PCCs (e.g., routers) and a PCE (e.g., SR-PCE) for path computation requests and responses.

Answer

BGP-LS

Answer

NETCONF

Answer

RESTCONF

Question 8

In the DiffServ model, which per-hop behavior (PHB) is associated with the AF31 DSCP value?

Accepted Answer

AF31. DSCP 26 (binary 011010) corresponds to AF31, which is part of the Assured Forwarding class with low drop probability and medium priority.

Answer

CS3

Answer

AF41

Answer

EF

Question 9

Which YANG data modeling construct is used to restrict a leaf value to be a reference to another leaf in the data tree?

Accepted Answer

leafref. The 'leafref' type in YANG is used to restrict the value of a leaf to refer to another leaf in the data tree, enforcing referential integrity.

Answer

when

Answer

must

Answer

choice

Question 10

In the Modular QoS CLI (MQC), which component is used to define traffic classes based on match criteria?

Accepted Answer

class-map. In the Modular QoS CLI (MQC), the class-map is the component used to define traffic classes by specifying match criteria such as IP precedence, DSCP values, or access-group references. The class-map groups packets that match one or more conditions, allowing the policy-map to apply QoS actions (e.g., policing, shaping) to that specific class. Without a class-map, the policy-map cannot differentiate between traffic types.

Answer

policy-map

Answer

access-list

Answer

service-policy

Question 11

An SP engineer is designing a QoS policy for a customer with three traffic classes: voice (priority), premium data (bandwidth guarantee), and best effort. The total bandwidth is 10 Mbps, with voice limited to 1 Mbps, premium data to 4 Mbps, and best effort to the remaining. Which policy-map configuration correctly uses LLQ and CBWFQ?

Accepted Answer

policy-map QOS
 class VOICE
  priority 1000
 class PREMIUM
  bandwidth 4000
 class class-default
  fair-queue. LLQ is used for voice (priority), CBWFQ for premium data (bandwidth), and default class for best effort.

Answer

policy-map QOS
 class VOICE
  priority percent 10
 class PREMIUM
  bandwidth percent 40
 class class-default
  shape average 5000

Answer

policy-map QOS
 class VOICE
  bandwidth 1000
 class PREMIUM
  priority 4000
 class class-default
  fair-queue

Answer

policy-map QOS
 class VOICE
  priority 1000
 class PREMIUM
  priority 4000
 class class-default
  fair-queue

Question 12

Which RESTCONF HTTP method is used to create a new data resource?

Accepted Answer

POST. RESTCONF uses POST to create a new data resource. PUT is used to replace or create, but POST is the standard for creation.

Answer

GET

Answer

PUT

Answer

DELETE

Question 13

Which two statements correctly describe the use of DSCP values in the DiffServ model? (Choose two.)

Accepted Answer

DSCP is a 6-bit field allowing 64 distinct values.. DSCP is a 6-bit field with 64 possible values. Per-hop behaviors (PHBs) like EF and AF are defined by DSCP values.

Answer

DSCP values are mapped to MPLS EXP bits at the egress PE.

Answer

DSCP values are used only for voice traffic.

Answer

DSCP value 0 indicates low latency traffic.

Question 14

Which three components are part of NSO (Network Services Orchestrator) architecture? (Choose three.)

Accepted Answer

YANG models for service definitions. YANG models are the foundation for service definitions in NSO because they define the data structures and constraints for network services using a standardized modeling language (RFC 6020/7950). NSO uses YANG to model both the service layer (customer-facing services) and the device layer (native device configurations), enabling service abstraction and multi-vendor orchestration.

Answer

RADIUS server

Answer

PCEP (Path Computation Element Protocol)

Question 15

Which two mechanisms are used for congestion avoidance in a QoS policy? (Choose two.)

Accepted Answer

WRED. WRED (Weighted Random Early Detection) and tail drop are congestion avoidance mechanisms that manage queue fullness before congestion occurs.

Answer

CBWFQ

Answer

Policing

Answer

LLQ