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Exam Code: JN0-664

Exam Name: Service Provider Routing and Switching, Professional (JNCIP-SP)

Certification Provider: Juniper

Corresponding Certification: JNCIP-SP

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Juniper JN0-664 Practice Test 38

Question 370

A service PE carries enterprise voice and bulk backups on the same uplink. Observed: Voice jitter rises during backup bursts although interface errors are zero. What evidence would validate recovery from this precise failure mode?

  1. Voice delay and jitter stay within the service objective during measured backup load.
  2. Counters show voice packets in the intended forwarding class before egress scheduling.
  3. Core label captures and queue counters show the intended premium treatment.
  4. Matching application flows receive the same forwarding class regardless of incoming port.

Explanation

Correct Answer

A:

The intended result is Voice delay and jitter stay within the service objective during measured backup load. It specifically verifies recovery from the default forwarding class treats latency-sensitive voice like best-effort traffic, which produced the original symptom: Voice jitter rises during backup bursts although interface errors are zero. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

B:

That observation would verify a separate fault involving a dscp classifier is not bound to the ingress traffic interface. Its symptom is Traffic with a valid voice DSCP enters the default best-effort queue. For this case the actual issue is the default forwarding class treats latency-sensitive voice like best-effort traffic, and the relevant success signal is Voice delay and jitter stay within the service objective during measured backup load.

C:

This result is useful in another case with evidence The core no longer preserves premium treatment across label-switched paths. It does not test recovery from voice jitter rises during backup bursts although interface errors are zero. Check instead whether voice delay and jitter stay within the service objective during measured backup load.

D:

It confirms an unrelated service correction: The firewall filter class action is attached on one ingress path but not the other. The present case reports Voice jitter rises during backup bursts although interface errors are zero. Its completion test is Voice delay and jitter stay within the service objective during measured backup load.

Question 371

A service PE carries enterprise voice and bulk backups on the same uplink. Observed: Voice jitter rises during backup bursts although interface errors are zero. What underlying protocol or service configuration problem best explains the evidence?

  1. The default forwarding class treats latency-sensitive voice like best-effort traffic.
  2. A DSCP classifier is not bound to the ingress traffic interface.
  3. IP classification was configured but MPLS EXP or traffic-class encoding was omitted.
  4. The firewall filter class action is attached on one ingress path but not the other.

Explanation

Correct Answer

A:

Because voice jitter rises during backup bursts although interface errors are zero, the likely cause is the default forwarding class treats latency-sensitive voice like best-effort traffic. It is testable: Classify approved voice flows into a suitable forwarding class and assign a protected scheduler. Expected follow-up: Voice delay and jitter stay within the service objective during measured backup load.

Incorrect Answers

B:

The stated cause is possible elsewhere but explains traffic with a valid voice dscp enters the default best-effort queue, not voice jitter rises during backup bursts although interface errors are zero. This incident is better attributed to the default forwarding class treats latency-sensitive voice like best-effort traffic.

C:

That explanation fits another condition: The core no longer preserves premium treatment across label-switched paths. The evidence here is Voice jitter rises during backup bursts although interface errors are zero. Its closer root cause is The default forwarding class treats latency-sensitive voice like best-effort traffic.

D:

The firewall filter class action is attached on one ingress path but not the other. would normally be accompanied by traffic is classified correctly only on one interface even though both see identical flows. The observed symptom is different: Voice jitter rises during backup bursts although interface errors are zero. The likely cause is The default forwarding class treats latency-sensitive voice like best-effort traffic.

Question 372

A service PE carries enterprise voice and bulk backups on the same uplink. Observed: Voice jitter rises during backup bursts although interface errors are zero. Which ongoing validation gate would best detect a recurrence of this problem?

  1. For each approved related change, verify that matching application flows receive the same forwarding class regardless of incoming port. Flag recurrence if traffic is classified correctly only on one interface even though both see identical flows.
  2. For each approved related change, verify that counters show voice packets in the intended forwarding class before egress scheduling. Flag recurrence if traffic with a valid voice DSCP enters the default best-effort queue.
  3. For each approved related change, verify that voice delay and jitter stay within the service objective during measured backup load. Flag recurrence if voice jitter rises during backup bursts although interface errors are zero.
  4. For each approved related change, verify that core label captures and queue counters show the intended premium treatment. Flag recurrence if the core no longer preserves premium treatment across label-switched paths.

Explanation

Correct Answer

C:

A useful regression gate tests whether voice delay and jitter stay within the service objective during measured backup load and alerts when voice jitter rises during backup bursts although interface errors are zero. This directly checks the technical weakness: The default forwarding class treats latency-sensitive voice like best-effort traffic. The gate is derived from the fictional incident and is not an independent Juniper engineer signoff.

Incorrect Answers

A:

This gate monitors a different failure, traffic is classified correctly only on one interface even though both see identical flows. It would not detect the current problem: Voice jitter rises during backup bursts although interface errors are zero. The appropriate check requires voice delay and jitter stay within the service objective during measured backup load.

B:

The proposed control is tied to a dscp classifier is not bound to the ingress traffic interface, typically observed when traffic with a valid voice DSCP enters the default best-effort queue. Here the target is the default forwarding class treats latency-sensitive voice like best-effort traffic; monitor voice delay and jitter stay within the service objective during measured backup load.

D:

It is valid for another service scenario but checks the core no longer preserves premium treatment across label-switched paths. This case instead needs a gate for voice jitter rises during backup bursts although interface errors are zero and evidence that voice delay and jitter stay within the service objective during measured backup load.

Question 373

A broadband aggregation router receives incoming DSCP-marked packets. Observed: Traffic with a valid voice DSCP enters the default best-effort queue. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Set the intended loss priority in the classifier or firewall filter actions.
  2. Apply the correct DSCP classification mapping on the ingress logical interface.
  3. Define compatible ingress MPLS traffic-class classification for the peer contract.
  4. Define and attach an authorized DSCP rewrite rule on the egress side.

Explanation

Correct Answer

B:

The observed condition is Traffic with a valid voice DSCP enters the default best-effort queue. That indicates a dscp classifier is not bound to the ingress traffic interface. Applying the proposed remedy directly changes that condition. A concrete completion check is: Counters show voice packets in the intended forwarding class before egress scheduling.

Incorrect Answers

A:

The option may be useful when policer counters rise but the wrong loss-priority bit is set internally, but that is not the current evidence. Here, traffic with a valid voice DSCP enters the default best-effort queue, indicating a dscp classifier is not bound to the ingress traffic interface. The targeted action is Apply the correct DSCP classification mapping on the ingress logical interface.

C:

This change belongs to a different Class of Service (CoS) issue: Premium traffic is delivered as best effort because the incoming label class is not decoded. That issue involves the ingress exp classifier does not map provider labels to local forwarding classes. The current symptom is Traffic with a valid voice DSCP enters the default best-effort queue. It instead requires apply the correct DSCP classification mapping on the ingress logical interface.

D:

This remediates the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint, normally indicated by Packets leave the WAN interface with DSCP zero despite correct internal classification. It would leave the observed problem (Traffic with a valid voice DSCP enters the default best-effort queue) unresolved. Address it with apply the correct DSCP classification mapping on the ingress logical interface.

Question 374

A broadband aggregation router receives incoming DSCP-marked packets. Observed: Traffic with a valid voice DSCP enters the default best-effort queue. After the correction, which result would most convincingly show that this fault is resolved?

  1. Internal class and loss-priority counters match the policy for each sample flow.
  2. Premium label values map to the correct internal class and egress scheduler.
  3. Captured outgoing frames retain the contracted DSCP markings.
  4. Counters show voice packets in the intended forwarding class before egress scheduling.

Explanation

Correct Answer

D:

After apply the correct DSCP classification mapping on the ingress logical interface, inspect whether counters show voice packets in the intended forwarding class before egress scheduling. This closes the loop between the reported observation (Traffic with a valid voice DSCP enters the default best-effort queue) and the underlying issue (A DSCP classifier is not bound to the ingress traffic interface).

Incorrect Answers

A:

That observation would verify a separate fault involving the policy sets a forwarding class but omits the packet-loss priority action. Its symptom is Policer counters rise but the wrong loss-priority bit is set internally. For this case the actual issue is a dscp classifier is not bound to the ingress traffic interface, and the relevant success signal is Counters show voice packets in the intended forwarding class before egress scheduling.

B:

It confirms an unrelated service correction: The ingress EXP classifier does not map provider labels to local forwarding classes. The present case reports Traffic with a valid voice DSCP enters the default best-effort queue. Its completion test is Counters show voice packets in the intended forwarding class before egress scheduling.

C:

This result is useful in another case with evidence Packets leave the WAN interface with DSCP zero despite correct internal classification. It does not test recovery from traffic with a valid voice dscp enters the default best-effort queue. Check instead whether counters show voice packets in the intended forwarding class before egress scheduling.

Question 375

A broadband aggregation router receives incoming DSCP-marked packets. Observed: Traffic with a valid voice DSCP enters the default best-effort queue. Which root cause is most consistent with this symptom?

  1. A DSCP classifier is not bound to the ingress traffic interface.
  2. The ingress EXP classifier does not map provider labels to local forwarding classes.
  3. The policy sets a forwarding class but omits the packet-loss priority action.
  4. The egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint.

Explanation

Correct Answer

A:

The reported evidence—Traffic with a valid voice DSCP enters the default best-effort queue—supports a dscp classifier is not bound to the ingress traffic interface. The appropriate intervention is to apply the correct DSCP classification mapping on the ingress logical interface, with confirmation from counters show voice packets in the intended forwarding class before egress scheduling. Other causes require actual device-state verification.

Incorrect Answers

B:

The ingress EXP classifier does not map provider labels to local forwarding classes. would normally be accompanied by premium traffic is delivered as best effort because the incoming label class is not decoded. The observed symptom is different: Traffic with a valid voice DSCP enters the default best-effort queue. The likely cause is A DSCP classifier is not bound to the ingress traffic interface.

C:

The stated cause is possible elsewhere but explains policer counters rise but the wrong loss-priority bit is set internally, not traffic with a valid voice dscp enters the default best-effort queue. This incident is better attributed to a dscp classifier is not bound to the ingress traffic interface.

D:

That explanation fits another condition: Packets leave the WAN interface with DSCP zero despite correct internal classification. The evidence here is Traffic with a valid voice DSCP enters the default best-effort queue. Its closer root cause is A DSCP classifier is not bound to the ingress traffic interface.

Question 376

A broadband aggregation router receives incoming DSCP-marked packets. Observed: Traffic with a valid voice DSCP enters the default best-effort queue. Which change-acceptance control is most relevant to preventing this exact failure?

  1. For each approved related change, verify that premium label values map to the correct internal class and egress scheduler. Flag recurrence if premium traffic is delivered as best effort because the incoming label class is not decoded.
  2. For each approved related change, verify that captured outgoing frames retain the contracted DSCP markings. Flag recurrence if packets leave the WAN interface with DSCP zero despite correct internal classification.
  3. For each approved related change, verify that counters show voice packets in the intended forwarding class before egress scheduling. Flag recurrence if traffic with a valid voice DSCP enters the default best-effort queue.
  4. For each approved related change, verify that internal class and loss-priority counters match the policy for each sample flow. Flag recurrence if policer counters rise but the wrong loss-priority bit is set internally.

Explanation

Correct Answer

C:

The control is specific to the initial failure. It requires the result Counters show voice packets in the intended forwarding class before egress scheduling. and treats Traffic with a valid voice DSCP enters the default best-effort queue. as a failure signal. The causal concern is a dscp classifier is not bound to the ingress traffic interface.

Incorrect Answers

A:

This gate monitors a different failure, premium traffic is delivered as best effort because the incoming label class is not decoded. It would not detect the current problem: Traffic with a valid voice DSCP enters the default best-effort queue. The appropriate check requires counters show voice packets in the intended forwarding class before egress scheduling.

B:

It is valid for another service scenario but checks packets leave the wan interface with dscp zero despite correct internal classification. This case instead needs a gate for traffic with a valid voice dscp enters the default best-effort queue and evidence that counters show voice packets in the intended forwarding class before egress scheduling.

D:

The proposed control is tied to the policy sets a forwarding class but omits the packet-loss priority action, typically observed when policer counters rise but the wrong loss-priority bit is set internally. Here the target is a dscp classifier is not bound to the ingress traffic interface; monitor counters show voice packets in the intended forwarding class before egress scheduling.

Question 377

A provider delivers a business VPN with negotiated expedited traffic. Observed: Packets leave the WAN interface with DSCP zero despite correct internal classification. What should the routing engineer change first to address this particular symptom?

  1. Assign the correct per-customer scheduler profile and respect parent capacity.
  2. Limit the high-priority offered rate and use appropriate scheduling for the remaining classes.
  3. Assign priority and bandwidth guarantees aligned with measured class demand and loss objectives.
  4. Define and attach an authorized DSCP rewrite rule on the egress side.

Explanation

Correct Answer

D:

The decisive evidence is that Packets leave the WAN interface with DSCP zero despite correct internal classification. This follows from the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint. The focused remedy is to define and attach an authorized DSCP rewrite rule on the egress side. Confirm improvement when captured outgoing frames retain the contracted DSCP markings. Validate on an approved lab or change window before touching production.

Incorrect Answers

A:

This remediates tenant-facing scheduler profiles were copied without evaluating each contracted committed rate, normally indicated by A new customer receives the same bandwidth guarantee as the largest existing customer. It would leave the observed problem (Packets leave the WAN interface with DSCP zero despite correct internal classification) unresolved. Address it with define and attach an authorized DSCP rewrite rule on the egress side.

B:

The option may be useful when other business queues starve whenever monitoring traffic floods, but that is not the current evidence. Here, packets leave the WAN interface with DSCP zero despite correct internal classification, indicating the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint. The targeted action is Define and attach an authorized DSCP rewrite rule on the egress side.

C:

This change belongs to a different Class of Service (CoS) issue: The premium application suffers sustained loss before any low-priority flow is dropped. That issue involves egress queue weights and scheduler priorities conflict with the sla. The current symptom is Packets leave the WAN interface with DSCP zero despite correct internal classification. It instead requires define and attach an authorized DSCP rewrite rule on the egress side.

Question 378

A provider delivers a business VPN with negotiated expedited traffic. Observed: Packets leave the WAN interface with DSCP zero despite correct internal classification. Which acceptance observation best confirms that the proposed change worked?

  1. Measured per-customer service rates match the individual contracts under shared load.
  2. Premium queue loss stays bounded while low-priority bursts are controlled.
  3. Critical monitoring meets latency objectives while business queues retain guaranteed service.
  4. Captured outgoing frames retain the contracted DSCP markings.

Explanation

Correct Answer

D:

This acceptance criterion tests the actual fault. The source evidence was Packets leave the WAN interface with DSCP zero despite correct internal classification. The correction addresses the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint; success requires captured outgoing frames retain the contracted DSCP markings.

Incorrect Answers

A:

This result is useful in another case with evidence A new customer receives the same bandwidth guarantee as the largest existing customer. It does not test recovery from packets leave the wan interface with dscp zero despite correct internal classification. Check instead whether captured outgoing frames retain the contracted DSCP markings.

B:

It confirms an unrelated service correction: Egress queue weights and scheduler priorities conflict with the SLA. The present case reports Packets leave the WAN interface with DSCP zero despite correct internal classification. Its completion test is Captured outgoing frames retain the contracted DSCP markings.

C:

That observation would verify a separate fault involving a strict-priority queue has no effective cap or rate control. Its symptom is Other business queues starve whenever monitoring traffic floods. For this case the actual issue is the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint, and the relevant success signal is Captured outgoing frames retain the contracted DSCP markings.

Question 379

A provider delivers a business VPN with negotiated expedited traffic. Observed: Packets leave the WAN interface with DSCP zero despite correct internal classification. What is the most likely source of the observed routing or service failure?

  1. Tenant-facing scheduler profiles were copied without evaluating each contracted committed rate.
  2. The egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint.
  3. A strict-priority queue has no effective cap or rate control.
  4. Egress queue weights and scheduler priorities conflict with the SLA.

Explanation

Correct Answer

B:

This explanation is the closest match to the observed symptom: Packets leave the WAN interface with DSCP zero despite correct internal classification. The specified root issue is The egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint. Repair it through define and attach an authorized DSCP rewrite rule on the egress side, then check captured outgoing frames retain the contracted DSCP markings.

Incorrect Answers

A:

That explanation fits another condition: A new customer receives the same bandwidth guarantee as the largest existing customer. The evidence here is Packets leave the WAN interface with DSCP zero despite correct internal classification. Its closer root cause is The egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint.

C:

The stated cause is possible elsewhere but explains other business queues starve whenever monitoring traffic floods, not packets leave the wan interface with dscp zero despite correct internal classification. This incident is better attributed to the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint.

D:

Egress queue weights and scheduler priorities conflict with the SLA. would normally be accompanied by the premium application suffers sustained loss before any low-priority flow is dropped. The observed symptom is different: Packets leave the WAN interface with DSCP zero despite correct internal classification. The likely cause is The egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint.

Question 380

A provider delivers a business VPN with negotiated expedited traffic. Observed: Packets leave the WAN interface with DSCP zero despite correct internal classification. What operational check best guards against this problem returning?

  1. For each approved related change, verify that premium queue loss stays bounded while low-priority bursts are controlled. Flag recurrence if the premium application suffers sustained loss before any low-priority flow is dropped.
  2. For each approved related change, verify that captured outgoing frames retain the contracted DSCP markings. Flag recurrence if packets leave the WAN interface with DSCP zero despite correct internal classification.
  3. For each approved related change, verify that measured per-customer service rates match the individual contracts under shared load. Flag recurrence if a new customer receives the same bandwidth guarantee as the largest existing customer.
  4. For each approved related change, verify that critical monitoring meets latency objectives while business queues retain guaranteed service. Flag recurrence if other business queues starve whenever monitoring traffic floods.

Explanation

Correct Answer

B:

This control asks for the same recovery evidence (Captured outgoing frames retain the contracted DSCP markings) and flags recurrence of the same failure (Packets leave the WAN interface with DSCP zero despite correct internal classification). It targets the underlying issue, the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

This gate monitors a different failure, the premium application suffers sustained loss before any low-priority flow is dropped. It would not detect the current problem: Packets leave the WAN interface with DSCP zero despite correct internal classification. The appropriate check requires captured outgoing frames retain the contracted DSCP markings.

C:

It is valid for another service scenario but checks a new customer receives the same bandwidth guarantee as the largest existing customer. This case instead needs a gate for packets leave the wan interface with dscp zero despite correct internal classification and evidence that captured outgoing frames retain the contracted DSCP markings.

D:

The proposed control is tied to a strict-priority queue has no effective cap or rate control, typically observed when other business queues starve whenever monitoring traffic floods. Here the target is the egress rewrite rule does not map forwarding class and loss priority to the agreed codepoint; monitor captured outgoing frames retain the contracted DSCP markings.

Service Provider Routing and Switching, Professional (JNCIP-SP) (JN0-664) Practice Tests