350-501 Automation and Quality of Services Practice Test 4 — 15 Questions

Question 1

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) is the congestion-avoidance mechanism that monitors average queue depth and probabilistically drops packets from lower-priority or non-ECN-marked flows before the queue hits 100%, preventing global synchronization and tail drop. It combines RED's early-drop behavior with IP precedence/DSCP weighting so higher-priority traffic is dropped less aggressively.

Answer

Policing

Answer

LLQ

Answer

CBWFQ

Question 2

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.. Option B is correct because the NETCONF operation is specifically designed to load configuration changes into a target datastore (such as running, candidate, or startup), allowing create, merge, replace, and delete operations on configuration data. Option D is correct because NETCONF defines SSH as its mandatory transport protocol (mapped to port 830), providing a secure, connection-oriented session over which the XML-based RPCs are exchanged. Option A is incorrect because retrieves both configuration and state data, while is the operation restricted to configuration data only. Option C is incorrect because NETCONF is an RPC/XML-based protocol, not a RESTful one, and does not use HTTP methods like POST and GET. Option E is incorrect because NETCONF encodes messages in XML, not JSON; JSON encoding is associated with RESTCONF.

Answer

get retrieves only operational state data.

Answer

NETCONF uses HTTP methods like POST and GET.

Answer

NETCONF uses JSON encoding by default.

Question 3

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 4

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 (Low Latency Queuing) provides strict priority queuing for voice traffic, ensuring it is served before other queues. To prevent voice from starving other traffic, policing on the priority queue is necessary to limit voice traffic to a configured rate. CBWFQ does not provide strict priority, FIFO does not prioritize, and WRED is a congestion avoidance mechanism, not a queuing mechanism for strict priority.

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 5

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). DSCP 46 (binary 101110) is the standard marking for Expedited Forwarding (EF) per-hop behavior, defined in RFC 3246, and is the recommended DSCP for VoIP bearer traffic to ensure low latency, low jitter, and low loss. EF provides a guaranteed minimum departure rate and is typically mapped to a priority queue in the network.

Answer

DSCP 34 (AF41)

Answer

DSCP 26 (AF31)

Answer

DSCP 0 (Best Effort)

Question 6

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

Accepted Answer

NETCONF. NSO (Network Services Orchestrator) uses NETCONF as its primary southbound protocol to communicate with network devices for configuration management. NETCONF provides a standardized, transactional, and model-driven (YANG) interface that allows NSO to push, validate, and roll back configuration changes reliably across multivendor devices.

Answer

RESTCONF

Answer

SNMP

Answer

CLI

Question 7

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.. Traffic shaping buffers excess packets and delays them to smooth out bursts, ensuring that the traffic rate conforms to the configured policy. Traffic policing, on the other hand, drops or re-marks packets that exceed the rate limit, without buffering them. This is the fundamental difference between the two mechanisms.

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 8

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 9

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 10

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 11

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 12

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 13

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. The correct policy-map uses 'priority 1000' for voice (LLQ, strict priority with 1 Mbps), 'bandwidth 4000' for premium data (CBWFQ, guaranteed 4 Mbps), and 'fair-queue' for class-default (best effort). This matches the requirement: voice gets priority, premium gets a bandwidth guarantee, and best effort uses remaining bandwidth.

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 14

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 15

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)