350-501 Automation and Quality of Services Practice Test 6 — 15 Questions

Question 1

In a hierarchical QoS policy applied to a subscriber aggregation interface, the parent policy shapes to 100 Mbps and the child policy allocates 50% bandwidth to voice and 50% to data. If voice traffic exceeds 50 Mbps, what happens to the excess?

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

Accepted Answer

Excess voice is dropped or re-marked. In a hierarchical QoS policy, the child policy's bandwidth allocation (50% to voice) is a guarantee/limit within the parent's shaped rate. If voice traffic exceeds its 50 Mbps share, the excess is not automatically given to the data class — it is either dropped or re-marked (e.g., policed down) depending on the child policy's configuration, because the child classes are bounded by their allocated percentages.

Answer

Excess voice is queued in the data queue

Answer

Excess voice is shaped by the parent policy

Answer

Excess voice is forwarded with best effort

Question 2

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 protocol for configuration management because NETCONF provides a standardized, transaction-based mechanism for editing device configurations using YANG data models. This allows NSO to perform atomic, rollback-capable configuration changes across multiple network devices, which is essential for service orchestration.

Answer

gRPC

Answer

SNMP

Answer

HTTP

Question 3

An SP engineer is using YANG to model a service. Which statement correctly describes the use of a 'leafref' type?

Accepted Answer

It restricts the leaf value to match another leaf's value. Leafref references an existing leaf in the YANG data tree, ensuring consistency.

Answer

It performs data validation using XPath

Answer

It defines a new leaf with a default value

Answer

It allows multiple values to be selected

Question 4

In the context of SR-PCE, which protocol does the PCE use to communicate with the path computation client (PCC) to set up SR-TE policies?

Accepted Answer

PCEP. PCEP (Path Computation Element Communication Protocol) is the standard protocol used between a PCE and a Path Computation Client (PCC) to request and receive path computations and to set up SR-TE policies. In SR-PCE deployments, the PCE uses PCEP to download the segment list to the head-end router, which instantiates the SR-TE policy.

Answer

NETCONF

Answer

OSPF

Answer

BGP-LS

Question 5

Which DSCP value corresponds to Best Effort (DF) per-hop behavior?

Accepted Answer

DSCP 0. DSCP 0 (binary 000000) is the Default Forwarding (DF) per-hop behavior, also called Best Effort. It is the default marking for packets that receive no special treatment in a QoS-enabled network. All other listed values map to specific Assured Forwarding or Expedited Forwarding classes.

Answer

DSCP 10

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DSCP 8

Answer

DSCP 46

Question 6

An SP uses NSO with a YANG service model to provision L3VPNs. Which database in NSO stores the configuration and state for all managed devices?

Accepted Answer

Configuration Database (CDB). The Configuration Database (CDB) is correct because NSO stores all service and device configuration in the CDB, which is the central transactional datastore that NSO reads and writes when provisioning L3VPNs via YANG service models. The CDB holds both the intended configuration and, through the operational data store, the state synchronized from managed devices.

Answer

Operational database

Answer

YANG repository

Answer

NED database

Question 7

What is the primary difference between traffic shaping and policing in a QoS implementation?

Accepted Answer

Shaping buffers excess traffic, policing drops or re-marks. Traffic shaping buffers excess traffic and delays it to smooth out bursts, while policing drops or re-marks excess traffic that exceeds the configured rate. Shaping is typically applied on egress to conform to a contracted rate, whereas policing is often applied on ingress to enforce a rate limit. The key difference is that shaping queues packets, while policing discards or marks them.

Answer

Shaping is applied at ingress, policing at egress

Answer

Shaping uses a token bucket, policing uses a leaky bucket

Answer

Shaping drops excess traffic, policing buffers it

Question 8

Which component in MQC is used to classify traffic based on match criteria?

Accepted Answer

Class-map. In Modular QoS CLI (MQC), the class-map is the component that defines the match criteria for classifying traffic. It specifies which packets belong to a particular class based on conditions like ACLs, DSCP, or protocol. The policy-map then references class-maps to apply actions.

Answer

Service-policy

Answer

Policy-map

Answer

Access-list

Question 9

Which THREE statements are true regarding NSO's NED? (Choose three.)

Accepted Answer

NED can support NETCONF, SNMP, or CLI as southbound protocols. NSO's NED (Network Equipment Driver) is the component that abstracts the southbound communication between NSO and network devices. NEDs can use NETCONF, SNMP, or CLI as the southbound protocol to translate NSO's device-independent configuration into device-specific commands, enabling multi-vendor management.

Answer

NED automatically generates YANG models

Answer

NED is used for path computation in SR-TE

Question 10

Which TWO methods can RESTCONF use to create a new data resource? (Choose two.)

Accepted Answer

POST. RESTCONF can create a new data resource using POST (option A), which targets a collection or list resource and creates a new child resource, with the server assigning the resource identifier and returning 201 Created. RESTCONF can also create a new data resource using PUT (option C), which creates the resource at a client-specified URI if it does not already exist, returning 201 Created (or 204 No Content if it replaces an existing resource). PATCH (option B) is used to modify or partially update an existing resource, not to create a new one. DELETE (option D) removes an existing resource, and GET (option E) only retrieves data, so neither creates a resource.

Answer

PATCH

Answer

DELETE

Answer

GET

Question 11

An SP is designing a QoS policy for a customer VPN that carries voice, video conferencing, and bulk data. The voice traffic requires low latency, video conferencing requires assured bandwidth, and bulk data should use any remaining bandwidth. Which queuing strategy should be applied on the PE-CE link?

Accepted Answer

LLQ with CBWFQ. LLQ (Low Latency Queuing) combined with CBWFQ provides a strict-priority queue for voice (minimizing latency and jitter) while CBWFQ guarantees bandwidth for video conferencing and fairly services bulk data with remaining bandwidth. This matches the three traffic classes' requirements exactly.

Answer

Policing with drop probability

Answer

FIFO with WRED

Answer

CBWFQ only

Question 12

An SP is deploying SR-TE policies using a central controller. The controller needs to compute paths based on bandwidth and latency constraints. Which protocol is used between the controller and the routers to signal the SR-TE policies?

Accepted Answer

PCEP. PCEP (Path Computation Element Communication Protocol, RFC 5440) is the protocol used between a Path Computation Element (PCE) — here the central controller — and Path Computation Clients (PCCs, the routers) to request, compute, and signal TE paths. In SR-TE deployments with a central controller, the controller uses PCEP to download the computed segment list to the head-end router, which then instantiates the SR-TE policy.

Answer

OSPF

Answer

BGP-LS

Answer

NETCONF

Question 13

An SP network engineer is reviewing a QoS configuration on a PE router. The policy-map uses a class for voice with the 'priority' command, and a class for video with 'bandwidth remaining percent 30'. What is the purpose of the 'bandwidth remaining percent' command?

Accepted Answer

It allocates a percentage of the bandwidth left after priority queues are served.. The 'bandwidth remaining percent' command allocates a percentage of the bandwidth that remains after priority (LLQ) queues have been served. It is a CBWFQ mechanism that ensures non-priority classes share the leftover bandwidth proportionally, preventing starvation while still respecting the strict priority of voice traffic. This is why it is used for video alongside a priority class for voice — video gets a guaranteed share of what's left, not a hard cap.

Answer

It sets the maximum bandwidth for the class.

Answer

It guarantees a minimum bandwidth for the class.

Answer

It enables Weighted Random Early Detection on the class.

Question 14

In the DiffServ model, which field is used in the IP header to mark packets for QoS treatment?

Accepted Answer

DSCP. The Differentiated Services Code Point (DSCP) is a 6-bit field in the IP header's Type of Service (ToS) byte, used to classify and mark packets for QoS treatment in the DiffServ model. It replaced the older 3-bit IP Precedence field and provides 64 possible classes. Network devices use DSCP values to apply per-hop behaviors such as expedited forwarding or assured forwarding.

Answer

IP Precedence

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802.1p

Answer

MPLS EXP

Question 15

An SP engineer is designing a QoS policy for a business customer with three traffic classes: Voice (critical latency), Transactional Data (low delay), and Bulk Data (no strict requirements). The link is 100 Mbps. Which TWO actions should be part of the policy? (Select two.)

Accepted Answer

Apply LLQ to the voice class with a policer to limit its rate to 10 Mbps.. Option B is correct because Low Latency Queuing (LLQ) gives the voice class strict priority scheduling, which minimizes latency and jitter for real-time traffic, and the 10 Mbps policer caps the priority queue so it cannot starve the other classes on the 100 Mbps link. Option E is correct because CBWFQ on the transactional data class guarantees a 30 Mbps bandwidth allocation, providing the low-delay, assured treatment that transactional traffic needs without requiring strict priority. Option A is not appropriate because FIFO offers no differentiated treatment and would not isolate bulk traffic from delay-sensitive classes. Option C is wrong because WRED is a congestion-avoidance drop mechanism unsuited to voice, which should be protected by priority queuing rather than early drops. Option D is wrong because a uniform 1000-packet queue limit ignores the differing latency and buffering needs of the three classes.

Answer

Use FIFO queuing for the bulk data class.

Answer

Use WRED on the voice class for congestion avoidance.

Answer

Set the queue limit to 1000 packets for all classes.