350-501 Automation and Quality of Services — Timed 25 Questions

Question 1

In the DiffServ model, which DSCP value is used for Expedited Forwarding (EF) to support voice traffic?

Accepted Answer

DSCP 46. EF is defined by DSCP 46 (binary 101110) to provide low-loss, low-latency service for voice.

Answer

DSCP 0

Answer

DSCP 40

Answer

DSCP 34

Question 2

An SP engineer is configuring hierarchical QoS on a PE router to enforce a per-subscriber bandwidth contract of 10 Mbps and prioritize voice within that contract. Which MQC configuration sequence is correct?

Accepted Answer

Define child class-map and policy-map with LLQ, then parent policy-map with shape and service-policy child, applied to interface.. Hierarchical QoS uses a parent policy for shaping and a child policy for classification and priority queuing. The child is applied to the parent's class-default.

Answer

Define parent policy-map with shape, then child policy-map with LLQ, apply child directly to interface.

Answer

Use policing in the parent policy to enforce 10 Mbps and child for LLQ.

Answer

Define one policy-map with both shape and LLQ in the same class.

Question 3

In an SP MPLS core, a PE router maps incoming DSCP values to MPLS EXP bits. Which statement about EXP marking is accurate when using the DiffServ Tunneling Model?

Accepted Answer

In Short Pipe model, the egress PE uses the original IP DSCP for queuing decisions, not the EXP.. In the DiffServ Tunneling Model, the Short Pipe model specifically instructs the egress PE to ignore the MPLS EXP bits for queuing and instead use the original IP DSCP value. This preserves the end-to-end QoS marking across the MPLS core, making option D correct. The Pipe model, by contrast, uses the EXP bits at the egress PE, which is why option B is incorrect.

Answer

EXP bits are always copied from the IP DSCP at the ingress PE.

Answer

In Pipe model, the egress PE uses EXP bits for queuing.

Answer

The MPLS EXP field is 6 bits, same as DSCP.

Question 4

An SP network uses NSO for service orchestration. Which component in NSO provides the abstraction layer to communicate with different device types using protocols like NETCONF or CLI?

Accepted Answer

NED. NEDs (Network Element Drivers) are plugins that translate NSO's service models to device-specific configurations.

Answer

YANG

Answer

RESTCONF

Answer

CDB

Question 5

When using NETCONF to edit a running configuration on a Cisco IOS XR router, which sequence of operations is correct?

Accepted Answer

, on candidate, , . NETCONF uses to modify the config; retrieves; prevents concurrent edits.

Answer

on candidate, then to running

Answer

<edit-config> on running, no lock needed

Answer

Question 6

In SR-TE PCE, which protocol does the PCE use to communicate with the PCC (Path Computation Client) to set up LSPs?

Accepted Answer

PCEP. In Segment Routing Traffic Engineering (SR-TE) with a Path Computation Element (PCE), the PCE communicates with the Path Computation Client (PCC) using the Path Computation Element Protocol (PCEP), as defined in RFC 5440 and extended for SR by RFC 8664. PCEP is specifically designed for path computation requests and responses, and for initiating and setting up LSPs via the PCE-initiated LSP stateful model (RFC 8281). The PCC sends path computation requests to the PCE, and the PCE responds with computed paths, which the PCC then uses to instantiate SR-TE LSPs.

Answer

RESTCONF

Answer

NETCONF

Answer

BGP-LS

Question 7

What is the primary difference between traffic policing and traffic shaping?

Accepted Answer

Shaping buffers excess traffic, while policing drops or re-marks it.. Policing drops or re-marks excess traffic; shaping buffers excess and smooths output.

Answer

Policing buffers excess traffic, while shaping drops it.

Answer

Policing is only applied inbound, shaping only outbound.

Answer

Both policing and shaping buffer excess traffic.

Question 8

An SP engineer is implementing LLQ on a PE router to prioritize voice. Which additional configuration is recommended to prevent voice traffic from starving other queues?

Accepted Answer

Configure a policer on the LLQ class to limit its rate.. Policing within the LLQ class limits the amount of traffic that can use the priority queue, preventing starvation.

Answer

Use CBWFQ without LLQ.

Answer

Disable queueing on other classes.

Answer

Set the priority queue bandwidth to 100%.

Question 9

In the context of YANG modeling for network automation, which statement about 'must' expressions is true?

Accepted Answer

They enforce a constraint that must be true for the data to be valid.. 'must' is an XPath expression that enforces a constraint on the data; if the condition is false, validation fails.

Answer

They conditionally make a leaf mandatory.

Answer

They are used to refine types.

Answer

They are used to define default values.

Question 10

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?

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 11

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 12

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 13

An SP engineer is implementing DSCP classification at the edge. Which two AF classes are typically used for mission-critical data? (Choose two.)

Accepted Answer

AF41. AF4x (e.g., AF41/AF42/AF43) and AF3x (e.g., AF31/AF32/AF33) are used for high-priority data. AF1x is low-priority.

Answer

CS0

Answer

AF11

Answer

AF22

Question 14

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

Accepted Answer

YANG service model. Option B is correct because 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 15

Which two HTTP methods are used in RESTCONF to retrieve configuration data? (Choose two.)

Accepted Answer

GET. GET retrieves data; POST can create but typically returns data; PATCH modifies; DELETE deletes.

Answer

POST

Answer

PATCH

Answer

PUT

Answer

DELETE

Question 16

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 17

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 18

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 19

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 20

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.