350-501 Automation and Quality of Services — 25 Questions

Question 1

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?

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

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 2

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 3

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 4

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 5

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 6

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

Accepted Answer

GET. In RESTCONF, the GET method is used to retrieve configuration data from the datastore. The other methods serve different purposes: POST creates data, PATCH partially modifies, PUT replaces or creates, and DELETE removes data. Therefore, only GET is correct for retrieval.

Answer

POST

Answer

PATCH

Answer

PUT

Answer

DELETE

Question 7

An SP engineer is configuring a policy-map to implement hierarchical QoS. Which two statements are correct when using MQC for hierarchical QoS? (Choose two.)

Accepted Answer

The child policy-map must include the bandwidth and priority commands to define queuing behavior.. Option B is correct because in a hierarchical MQC configuration the child (or lower-level) policy-map is where the actual queuing and scheduling actions are defined, so it must contain commands such as bandwidth (for class-based weighted fair queuing guarantees) and priority (for low-latency queuing) to shape per-class behavior. Option C is correct because the parent policy-map performs the overall rate limiting/aggregate shaping via the shape command and then references the child policy-map with the service-policy command, creating the hierarchical relationship. Option D is correct because the complete hierarchy is activated by attaching the parent policy-map to the interface with the service-policy command (service-policy output parent-name), which is the standard MQC attachment point. Option A is incorrect because hierarchical QoS in MQC supports up to three levels of nesting (parent, child, and grandchild), not only two. Option E is incorrect because shape and priority are applied at different levels of the hierarchy — shaping in the parent and priority/bandwidth queuing in the child — and configuring both in the same policy-map would not produce a valid hierarchical QoS structure.

Answer

Hierarchical QoS supports only two levels of nesting.

Answer

Both shape and priority commands must be configured in the same policy-map.

Question 8

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 9

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 10

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

Accepted Answer

WRED. WRED (B) is correct because Weighted Random Early Detection is a congestion-avoidance mechanism that proactively drops lower-priority packets before a queue fills, preventing tail drop and TCP global synchronization. Tail drop (E) is also correct because it is the default congestion-avoidance behavior on full queues, dropping packets once the queue reaches its maximum threshold. CBWFQ (A) is a queuing/scheduling mechanism, not congestion avoidance. Policing (C) is a traffic-conditioning mechanism that drops or remarks excess traffic to enforce a rate limit, not a queue congestion-avoidance technique. LLQ (D) is a low-latency queuing/scheduling mechanism that provides priority treatment, not congestion avoidance.

Answer

CBWFQ

Answer

Policing

Answer

LLQ

Question 11

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?

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

Accepted Answer

To drop excess voice traffic and prevent starvation of other queues. In hierarchical QoS (HQoS), the parent policy shapes the aggregate traffic to 10 Mbps, while the child policy applies LLQ for voice and CBWFQ for data. The primary purpose of policing within the LLQ child policy is to enforce a strict rate limit on voice traffic, dropping excess packets to prevent voice from consuming bandwidth beyond its allocated share. This prevents voice traffic from starving other queues (e.g., data) within the shaped parent rate, ensuring fairness and protecting other classes from congestion.

Answer

To re-mark voice traffic to a lower DSCP

Answer

To police the parent shape rate

Answer

To buffer excess voice traffic

Question 12

An SP uses NSO for service orchestration. A new service requires YANG data validation to ensure that the 'bandwidth' leaf does not exceed 10000 kbps when the 'service-type' is 'premium'. Which YANG statement is appropriate?

Accepted Answer

must '. <= 10000' { error-message 'Bandwidth too high'; }. The 'must' statement in YANG is used to define constraints that must be satisfied. Here, the constraint is that the 'bandwidth' leaf must not exceed 10000 when 'service-type' is 'premium'. The 'must' expression '. <= 10000' checks the value of the current node (bandwidth) against 10000. This is the appropriate statement.

Answer

when '. <= 10000'

Answer

leafref bandwidth { path '../bandwidth-limit'; }

Answer

range '0..10000';

Question 13

An SP network experiences congestion on a core link. The QoS policy uses CBWFQ with classes for voice (LLQ), video (bandwidth 30%), and data (bandwidth 50%). During congestion, voice traffic spikes to 25% of the link. What happens to video and data traffic?

Accepted Answer

Video and data share the remaining 75% as per their bandwidth percentages. With CBWFQ and LLQ, the voice class is served by a strict priority queue that is policed at its configured rate. Once voice exceeds its allocated bandwidth, excess voice is dropped, but the guaranteed bandwidth percentages for the remaining classes (video 30%, data 50%) are still honored. The leftover 75% of link capacity is distributed between video and data according to their configured bandwidth percentages, so video gets 30/80 and data gets 50/80 of the remaining bandwidth.

Answer

Video and data are dropped entirely until voice subsides

Answer

Video and data are unaffected

Answer

Video and data are treated as best effort

Question 14

In a CBWFQ policy with LLQ, which statement is true regarding the bandwidth command for non-priority classes?

Accepted Answer

The sum of bandwidth for all classes must be less than 100%. The bandwidth command can specify a percentage or absolute bandwidth, but the sum must not exceed the available bandwidth (interface bandwidth minus LLQ).

Answer

The bandwidth can exceed the interface speed if shaped

Answer

Bandwidth is not used if LLQ is present

Answer

The bandwidth command is optional in CBWFQ

Question 15

An SP is implementing DiffServ at the edge router. Which TWO DSCP values are used for AF41 and AF31, respectively? (Choose two.)

Accepted Answer

DSCP 26. DSCP 34 (option E) is correct because AF41 is encoded as class 4, drop precedence 1: 4×8 + 2×1 = 34, giving the binary pattern 100010. DSCP 26 (option B) is correct because AF31 is class 3, drop precedence 1: 3×8 + 2×1 = 26, giving 011010. These AF codepoints let the edge router mark assured-forwarding traffic with distinct classes and low drop precedence. DSCP 10 (option A) is AF11, not AF31 or AF41; DSCP 46 (option C) is EF, used for expedited forwarding; and DSCP 18 (option D) is AF21, so none of those match the requested AF41/AF31 values.

Answer

DSCP 10

Answer

DSCP 46

Answer

DSCP 18

Question 16

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?

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

Accepted Answer

Parent shape 10 Mbps, child policy with LLQ for voice and CBWFQ for video and data with bandwidth 5 Mbps each. The correct configuration must ensure that the child policy's bandwidth guarantees sum to no more than the parent shape rate (10 Mbps) and that voice gets priority treatment. Option A uses LLQ for voice (priority) and CBWFQ for video and data with bandwidth 5 Mbps each, totaling 10 Mbps, which fits within the parent shape. This provides guaranteed bandwidth for voice and video while allowing data to use the remaining capacity.

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

Answer

Parent shape 10 Mbps, child policy with bandwidth 2 Mbps for voice, 4 Mbps for video, and default class for data

Question 17

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

Accepted Answer

DSCP 46. DSCP 46 corresponds to the Expedited Forwarding (EF) per-hop behavior defined in RFC 3246, which is the standard marking for voice traffic requiring low latency, low jitter, and low loss. The decimal value 46 maps to binary 101110, and its upper three bits (101) place it in the IP Precedence 5 class historically used for voice.

Answer

DSCP 48

Answer

DSCP 34

Answer

DSCP 0

Question 18

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. Cisco NSO uses NETCONF as the primary southbound protocol to push configuration to network devices, with YANG models defining the data schema. The NED (Network Element Driver) translates NSO's service model into device-specific NETCONF RPCs, typically over SSH on port 830.

Answer

CLI

Answer

PCEP

Answer

SNMP

Question 19

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.. Option D is correct because policing is typically implemented with a token bucket that can take actions such as re-marking out-of-profile packets to a lower DSCP (e.g., via MQC policy-map with 'police ... conform-action ... exceed-action set-dscp-transmit'), whereas shaping only delays packets and has no re-marking action. Option E is correct because shaping uses a token bucket with a queue/buffer to delay excess traffic so it conforms to the committed rate, while policing drops or re-marks packets that exceed the configured rate rather than buffering them. Option A is incorrect because shaping, not policing, introduces delay by buffering excess traffic; policing generally adds little delay. Option B is incorrect because both shaping and policing are typically applied on egress (outbound) interfaces, and shaping is not an ingress-only function. Option C is incorrect because shaping normally does not drop packets—it buffers and delays them—while policing may drop or re-mark, so neither always causes packet loss.

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 20

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

Accepted Answer

DSCP 34. The Assured Forwarding (AF) class 4 consists of AF41, AF42, and AF43, whose DSCP values are 34, 36, and 38 respectively, so options A (DSCP 34), C (DSCP 36), and E (DSCP 38) are correct. AF4x is encoded as class 4 with drop precedence 1, 2, or 3, giving binary 100xx0 and decimal values 34, 36, and 38. Option B (DSCP 40) belongs to AF class 5 as AF41? No, DSCP 40 is AF41? Actually AF41 is 34, so 40 is CS5? DSCP 40 is CS5, not AF4. Option D (DSCP 46) is Expedited Forwarding (EF), not part of AF class 4. Therefore B and D are incorrect.

Answer

DSCP 40

Answer

DSCP 46