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

Question 1

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 provides a strict priority queue for voice (low latency) and CBWFQ for other classes with bandwidth guarantees. Video conferencing can be assigned to a class with a bandwidth percent, and bulk data to the default class with fair queuing.

Answer

Policing with drop probability

Answer

FIFO with WRED

Answer

CBWFQ only

Question 2

An SP engineer is configuring hierarchical QoS on a PE router for a subscriber with a 10 Mbps shaped rate. The child policy must guarantee 2 Mbps for voice, 4 Mbps for video, and the rest for data. However, the parent policy shape rate is 10 Mbps. Which configuration ensures proper operation?

Accepted Answer

Parent shape 10 Mbps, child policy with bandwidth 2 Mbps for voice, 4 Mbps for video, and default class for data. In hierarchical QoS, the child policy's total bandwidth should not exceed the parent shape rate. The child policy allocates bandwidth percentages relative to the parent shape. If video and voice together exceed the shape, congestion may cause drops. The correct approach is to allocate bandwidth within the shape rate.

Answer

Parent shape 10 Mbps, child policy with LLQ for voice and CBWFQ for video and data with bandwidth 5 Mbps each

Answer

Parent shape 10 Mbps, child policy with priority for voice and bandwidth 4 Mbps for video, no data class

Answer

Parent shape 10 Mbps, child policy with bandwidth percent 20 voice, 40 video, and 40 data

Question 3

Which DSCP value is recommended for Expedited Forwarding (EF) per-hop behavior, commonly used for voice traffic?

Accepted Answer

DSCP 46. EF is defined as DSCP 46 (binary 101110) for low-loss, low-latency traffic like voice.

Answer

DSCP 48

Answer

DSCP 34

Answer

DSCP 0

Question 4

An SP uses NSO to orchestrate MPLS L3VPN services. The service model is written in YANG, and the NED communicates with the PE routers. Which protocol does NSO use to push configuration to the network devices?

Accepted Answer

NETCONF. NSO can use NETCONF or RESTCONF southbound to communicate with network devices. NETCONF is the standard for configuration management.

Answer

CLI

Answer

PCEP

Answer

SNMP

Question 5

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 Protocol) is used for communication between a PCE (controller) and PCC (router) to compute and instantiate SR-TE policies.

Answer

OSPF

Answer

BGP-LS

Answer

NETCONF

Question 6

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.. 'bandwidth remaining percent' allocates a percentage of the remaining bandwidth after the priority queue is serviced. This ensures other classes share leftover bandwidth.

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 7

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

Accepted Answer

DSCP. The DiffServ model uses the 6-bit DSCP field in the IP header to classify packets.

Answer

IP Precedence

Answer

802.1p

Answer

MPLS EXP

Question 8

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.. LLQ provides strict priority for voice. CBWFQ with bandwidth guarantees for transactional data ensures it gets capacity. Bulk data can use remaining bandwidth.

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.

Question 9

An SP is deploying a Network Services Orchestrator (NSO) for service automation. Which THREE components are integral to NSO architecture? (Select three.)

Accepted Answer

Configuration Database (CDB) for storing state. NSO uses a Configuration Database (CDB) for storing device configurations, YANG models for service definitions, and NEDs (Network Element Drivers) for device abstraction.

Answer

SNMP trap receiver for event monitoring

Answer

Path Computation Element (PCE) for TE

Question 10

An SP is implementing traffic shaping on an MPLS PE-CE link. Which TWO statements are true about shaping compared to policing? (Select two.)

Accepted Answer

Policing can re-mark packets to a lower DSCP, shaping cannot.. Shaping buffers excess traffic to smooth bursts, while policing drops or re-marks excess packets. Shaping introduces delay due to buffering; policing can cause TCP retransmissions.

Answer

Policing typically introduces more delay than shaping.

Answer

Shaping is applied on ingress, policing on egress.

Answer

Both shaping and policing always result in packet loss.

Question 11

Which THREE DSCP values are part of the Assured Forwarding (AF) class 4? (Select three.)

Accepted Answer

DSCP 34. AF4 has three drop probabilities: low (AF41 = DSCP 34), medium (AF42 = DSCP 36), high (AF43 = DSCP 38).

Answer

DSCP 40

Answer

DSCP 46

Question 12

An SP is using MQC to configure QoS on a core router. Which TWO statements about MQC are correct? (Select two.)

Accepted Answer

A class-map can match multiple criteria using 'match-all' or 'match-any'.. MQC consists of class-map (classification), policy-map (define actions), and service-policy (apply). class-map uses match statements; policy-map can include bandwidth, priority, shape, etc.

Answer

A policy-map can be applied globally to all interfaces.

Answer

The 'service-policy' command is used in global configuration mode.

Answer

WRED can only be configured within a policy-map class.

Question 13

An SP is deploying SR-PCE for centralized traffic engineering. Which THREE functions does the PCE perform? (Select three.)

Accepted Answer

Computes path for traffic-engineered LSPs based on constraints.. PCE computes paths based on constraints, communicates via PCEP with routers (PCCs), and can instantiate SR-TE policies.

Answer

Distributes link-state information using BGP-LS.

Answer

Configures MPLS forwarding on routers.

Question 14

An SP engineer is configuring QoS on a PE router for MPLS traffic. The core network uses MPLS EXP bits for QoS. Which TWO methods can be used to set MPLS EXP bits based on IP DSCP? (Select two.)

Accepted Answer

Use a policy-map with 'set mpls experimental' command.. On Cisco routers, you can use 'set mpls experimental imposition' to set EXP on the imposed label, or use a QoS policy with 'set mpls experimental' in a policy-map.

Answer

Configure 'mpls qos enforce' on the interface.

Answer

Configure 'mpls ip' to automatically copy DSCP to EXP.

Answer

Apply 'qos-group' to DSCP mapping.

Question 15

Which THREE of the following are standard per-hop behaviors (PHBs) in the DiffServ model? (Select three.)

Accepted Answer

Default (Best Effort). The DiffServ model defines EF (Expedited Forwarding), AF (Assured Forwarding), and Default (BE) PHBs. CS is Class Selector, but not a separate PHB; it is part of AF? Actually CS is a backward-compatible PHB. Standard ones are EF, AF, and Default.

Answer

LLQ

Answer

CS (Class Selector)