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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 43

Question 420

A metro PE carries internet and private VPN traffic over one 10G interface. Observed: VPN queue counters show no packets despite known VPN load. Which ongoing validation gate would best detect a recurrence of this problem?

  1. For each approved related change, verify that vPN packets increment the intended queue counters and receive the agreed service. Flag recurrence if vPN queue counters show no packets despite known VPN load.
  2. For each approved related change, verify that in-profile traffic passes and only true excess traffic is policed. Flag recurrence if business telemetry is discarded even when its contracted rate is not exceeded.
  3. For each approved related change, verify that queue telemetry shows configured early-drop behavior before hard buffer exhaustion. Flag recurrence if tail drops occur abruptly rather than the expected early-drop progression.
  4. For each approved related change, verify that routing sessions remain healthy while excess guest traffic is rate-limited. Flag recurrence if bGP keepalives are delayed under volumetric guest transit load.

Explanation

Correct Answer

A:

A useful regression gate tests whether vPN packets increment the intended queue counters and receive the agreed service and alerts when vPN queue counters show no packets despite known VPN load. This directly checks the technical weakness: Classifier and forwarding-class mappings do not match the chosen VPN traffic selector. The gate is derived from the fictional incident and is not an independent Juniper engineer signoff.

Incorrect Answers

B:

This gate monitors a different failure, business telemetry is discarded even when its contracted rate is not exceeded. It would not detect the current problem: VPN queue counters show no packets despite known VPN load. The appropriate check requires vPN packets increment the intended queue counters and receive the agreed service.

C:

The proposed control is tied to the wred drop-profile threshold curve or attachment is incorrect, typically observed when tail drops occur abruptly rather than the expected early-drop progression. Here the target is classifier and forwarding-class mappings do not match the chosen vpn traffic selector; monitor vPN packets increment the intended queue counters and receive the agreed service.

D:

It is valid for another service scenario but checks bgp keepalives are delayed under volumetric guest transit load. This case instead needs a gate for vpn queue counters show no packets despite known vpn load and evidence that vPN packets increment the intended queue counters and receive the agreed service.

Question 421

A provider tests an application class with WRED enabled. Observed: Tail drops occur abruptly rather than the expected early-drop progression. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Review average queue depth thresholds and attach the intended drop profile to the proper scheduler.
  2. Create supported low-latency treatment with suitable class classification and queue scheduling.
  3. Inspect per-queue offered rate and adjust guarantees and drop settings to actual demand.
  4. Establish supported hierarchical scheduler and parent shaping policy.

Explanation

Correct Answer

A:

The observed condition is Tail drops occur abruptly rather than the expected early-drop progression. That indicates the wred drop-profile threshold curve or attachment is incorrect. Applying the proposed remedy directly changes that condition. A concrete completion check is: Queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

Incorrect Answers

B:

This remediates no separate class queue protects delay-sensitive packets from serialization backlog, normally indicated by A single FIFO queue holds both low-latency and bulk data traffic. It would leave the observed problem (Tail drops occur abruptly rather than the expected early-drop progression) unresolved. Address it with review average queue depth thresholds and attach the intended drop profile to the proper scheduler.

C:

This change belongs to a different Class of Service (CoS) issue: Application packet loss remains high even with low measured total interface utilization. That issue involves queue-specific congestion and scheduler weights hide localized buffer exhaustion. The current symptom is Tail drops occur abruptly rather than the expected early-drop progression. It instead requires review average queue depth thresholds and attach the intended drop profile to the proper scheduler.

D:

The option may be useful when subinterfaces together exceed the parent shaping budget during congestion, but that is not the current evidence. Here, tail drops occur abruptly rather than the expected early-drop progression, indicating the wred drop-profile threshold curve or attachment is incorrect. The targeted action is Review average queue depth thresholds and attach the intended drop profile to the proper scheduler.

Question 422

A provider tests an application class with WRED enabled. Observed: Tail drops occur abruptly rather than the expected early-drop progression. After the correction, which result would most convincingly show that this fault is resolved?

  1. Voice packets experience controlled latency while bulk traffic retains available capacity.
  2. Queue telemetry shows configured early-drop behavior before hard buffer exhaustion.
  3. Video queue occupancy and packet loss improve under equivalent traffic replay.
  4. Aggregate egress stays within the contracted parent rate and class priorities remain intact.

Explanation

Correct Answer

B:

After review average queue depth thresholds and attach the intended drop profile to the proper scheduler, inspect whether queue telemetry shows configured early-drop behavior before hard buffer exhaustion. This closes the loop between the reported observation (Tail drops occur abruptly rather than the expected early-drop progression) and the underlying issue (The WRED drop-profile threshold curve or attachment is incorrect).

Incorrect Answers

A:

This result is useful in another case with evidence A single FIFO queue holds both low-latency and bulk data traffic. It does not test recovery from tail drops occur abruptly rather than the expected early-drop progression. Check instead whether queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

C:

It confirms an unrelated service correction: Queue-specific congestion and scheduler weights hide localized buffer exhaustion. The present case reports Tail drops occur abruptly rather than the expected early-drop progression. Its completion test is Queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

D:

That observation would verify a separate fault involving per-customer shapers are configured without enforcing a proper aggregate parent limit. Its symptom is Subinterfaces together exceed the parent shaping budget during congestion. For this case the actual issue is the wred drop-profile threshold curve or attachment is incorrect, and the relevant success signal is Queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

Question 423

A provider tests an application class with WRED enabled. Observed: Tail drops occur abruptly rather than the expected early-drop progression. Which root cause is most consistent with this symptom?

  1. No separate class queue protects delay-sensitive packets from serialization backlog.
  2. The WRED drop-profile threshold curve or attachment is incorrect.
  3. Queue-specific congestion and scheduler weights hide localized buffer exhaustion.
  4. Per-customer shapers are configured without enforcing a proper aggregate parent limit.

Explanation

Correct Answer

B:

The reported evidence—Tail drops occur abruptly rather than the expected early-drop progression—supports the wred drop-profile threshold curve or attachment is incorrect. The appropriate intervention is to review average queue depth thresholds and attach the intended drop profile to the proper scheduler, with confirmation from queue telemetry shows configured early-drop behavior before hard buffer exhaustion. Other causes require actual device-state verification.

Incorrect Answers

A:

That explanation fits another condition: A single FIFO queue holds both low-latency and bulk data traffic. The evidence here is Tail drops occur abruptly rather than the expected early-drop progression. Its closer root cause is The WRED drop-profile threshold curve or attachment is incorrect.

C:

Queue-specific congestion and scheduler weights hide localized buffer exhaustion. would normally be accompanied by application packet loss remains high even with low measured total interface utilization. The observed symptom is different: Tail drops occur abruptly rather than the expected early-drop progression. The likely cause is The WRED drop-profile threshold curve or attachment is incorrect.

D:

The stated cause is possible elsewhere but explains subinterfaces together exceed the parent shaping budget during congestion, not tail drops occur abruptly rather than the expected early-drop progression. This incident is better attributed to the wred drop-profile threshold curve or attachment is incorrect.

Question 424

A provider tests an application class with WRED enabled. Observed: Tail drops occur abruptly rather than the expected early-drop progression. Which change-acceptance control is most relevant to preventing this exact failure?

  1. For each approved related change, verify that video queue occupancy and packet loss improve under equivalent traffic replay. Flag recurrence if application packet loss remains high even with low measured total interface utilization.
  2. For each approved related change, verify that voice packets experience controlled latency while bulk traffic retains available capacity. Flag recurrence if a single FIFO queue holds both low-latency and bulk data traffic.
  3. For each approved related change, verify that aggregate egress stays within the contracted parent rate and class priorities remain intact. Flag recurrence if subinterfaces together exceed the parent shaping budget during congestion.
  4. For each approved related change, verify that queue telemetry shows configured early-drop behavior before hard buffer exhaustion. Flag recurrence if tail drops occur abruptly rather than the expected early-drop progression.

Explanation

Correct Answer

D:

The control is specific to the initial failure. It requires the result Queue telemetry shows configured early-drop behavior before hard buffer exhaustion. and treats Tail drops occur abruptly rather than the expected early-drop progression. as a failure signal. The causal concern is the wred drop-profile threshold curve or attachment is incorrect.

Incorrect Answers

A:

This gate monitors a different failure, application packet loss remains high even with low measured total interface utilization. It would not detect the current problem: Tail drops occur abruptly rather than the expected early-drop progression. The appropriate check requires queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

B:

It is valid for another service scenario but checks a single fifo queue holds both low-latency and bulk data traffic. This case instead needs a gate for tail drops occur abruptly rather than the expected early-drop progression and evidence that queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

C:

The proposed control is tied to per-customer shapers are configured without enforcing a proper aggregate parent limit, typically observed when subinterfaces together exceed the parent shaping budget during congestion. Here the target is the wred drop-profile threshold curve or attachment is incorrect; monitor queue telemetry shows configured early-drop behavior before hard buffer exhaustion.

Question 425

A customer complains that small voice packets are delayed by large packets. Observed: A single FIFO queue holds both low-latency and bulk data traffic. What should the routing engineer change first to address this particular symptom?

  1. Restore the intended multicast classification entry and corresponding scheduler.
  2. Separate packet-loss priority and apply compatible weighted random early drop profiles.
  3. Attach a coherent 802.1p rewrite policy for supported tagged egress frames.
  4. Create supported low-latency treatment with suitable class classification and queue scheduling.

Explanation

Correct Answer

D:

The decisive evidence is that A single FIFO queue holds both low-latency and bulk data traffic. This follows from no separate class queue protects delay-sensitive packets from serialization backlog. The focused remedy is to create supported low-latency treatment with suitable class classification and queue scheduling. Confirm improvement when voice packets experience controlled latency while bulk traffic retains available capacity. Validate on an approved lab or change window before touching production.

Incorrect Answers

A:

The option may be useful when multicast video packets are assigned to the lowest-priority class after a classifier update, but that is not the current evidence. Here, a single FIFO queue holds both low-latency and bulk data traffic, indicating no separate class queue protects delay-sensitive packets from serialization backlog. The targeted action is Create supported low-latency treatment with suitable class classification and queue scheduling.

B:

This remediates classification does not assign distinct packet-loss priorities for drop behavior, normally indicated by Both important and disposable video packets are dropped equally in congestion. It would leave the observed problem (A single FIFO queue holds both low-latency and bulk data traffic) unresolved. Address it with create supported low-latency treatment with suitable class classification and queue scheduling.

C:

This change belongs to a different Class of Service (CoS) issue: The 802.1p priority observed downstream no longer matches the agreed enterprise service class. That issue involves an egress ieee 802.1p rewrite map is absent or maps the wrong forwarding class. The current symptom is A single FIFO queue holds both low-latency and bulk data traffic. It instead requires create supported low-latency treatment with suitable class classification and queue scheduling.

Question 426

A customer complains that small voice packets are delayed by large packets. Observed: A single FIFO queue holds both low-latency and bulk data traffic. Which acceptance observation best confirms that the proposed change worked?

  1. Congestion counters show preferential dropping of disposable packets.
  2. Voice packets experience controlled latency while bulk traffic retains available capacity.
  3. Multicast packets land in the approved class and video impairment disappears.
  4. Downstream tag captures show the intended priority codepoint values.

Explanation

Correct Answer

B:

This acceptance criterion tests the actual fault. The source evidence was A single FIFO queue holds both low-latency and bulk data traffic. The correction addresses no separate class queue protects delay-sensitive packets from serialization backlog; success requires voice packets experience controlled latency while bulk traffic retains available capacity.

Incorrect Answers

A:

This result is useful in another case with evidence Both important and disposable video packets are dropped equally in congestion. It does not test recovery from a single fifo queue holds both low-latency and bulk data traffic. Check instead whether voice packets experience controlled latency while bulk traffic retains available capacity.

C:

That observation would verify a separate fault involving the updated dscp-to-forwarding-class table misses the multicast source marking. Its symptom is Multicast video packets are assigned to the lowest-priority class after a classifier update. For this case the actual issue is no separate class queue protects delay-sensitive packets from serialization backlog, and the relevant success signal is Voice packets experience controlled latency while bulk traffic retains available capacity.

D:

It confirms an unrelated service correction: An egress IEEE 802.1p rewrite map is absent or maps the wrong forwarding class. The present case reports A single FIFO queue holds both low-latency and bulk data traffic. Its completion test is Voice packets experience controlled latency while bulk traffic retains available capacity.

Question 427

A customer complains that small voice packets are delayed by large packets. Observed: A single FIFO queue holds both low-latency and bulk data traffic. What is the most likely source of the observed routing or service failure?

  1. An egress IEEE 802.1p rewrite map is absent or maps the wrong forwarding class.
  2. The updated DSCP-to-forwarding-class table misses the multicast source marking.
  3. No separate class queue protects delay-sensitive packets from serialization backlog.
  4. Classification does not assign distinct packet-loss priorities for drop behavior.

Explanation

Correct Answer

C:

This explanation is the closest match to the observed symptom: A single FIFO queue holds both low-latency and bulk data traffic. The specified root issue is No separate class queue protects delay-sensitive packets from serialization backlog. Repair it through create supported low-latency treatment with suitable class classification and queue scheduling, then check voice packets experience controlled latency while bulk traffic retains available capacity.

Incorrect Answers

A:

An egress IEEE 802.1p rewrite map is absent or maps the wrong forwarding class. would normally be accompanied by the 802.1p priority observed downstream no longer matches the agreed enterprise service class. The observed symptom is different: A single FIFO queue holds both low-latency and bulk data traffic. The likely cause is No separate class queue protects delay-sensitive packets from serialization backlog.

B:

The stated cause is possible elsewhere but explains multicast video packets are assigned to the lowest-priority class after a classifier update, not a single fifo queue holds both low-latency and bulk data traffic. This incident is better attributed to no separate class queue protects delay-sensitive packets from serialization backlog.

D:

That explanation fits another condition: Both important and disposable video packets are dropped equally in congestion. The evidence here is A single FIFO queue holds both low-latency and bulk data traffic. Its closer root cause is No separate class queue protects delay-sensitive packets from serialization backlog.

Question 428

A customer complains that small voice packets are delayed by large packets. Observed: A single FIFO queue holds both low-latency and bulk data traffic. What operational check best guards against this problem returning?

  1. For each approved related change, verify that congestion counters show preferential dropping of disposable packets. Flag recurrence if both important and disposable video packets are dropped equally in congestion.
  2. For each approved related change, verify that multicast packets land in the approved class and video impairment disappears. Flag recurrence if multicast video packets are assigned to the lowest-priority class after a classifier update.
  3. For each approved related change, verify that voice packets experience controlled latency while bulk traffic retains available capacity. Flag recurrence if a single FIFO queue holds both low-latency and bulk data traffic.
  4. For each approved related change, verify that downstream tag captures show the intended priority codepoint values. Flag recurrence if the 802.1p priority observed downstream no longer matches the agreed enterprise service class.

Explanation

Correct Answer

C:

This control asks for the same recovery evidence (Voice packets experience controlled latency while bulk traffic retains available capacity) and flags recurrence of the same failure (A single FIFO queue holds both low-latency and bulk data traffic). It targets the underlying issue, no separate class queue protects delay-sensitive packets from serialization backlog, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

It is valid for another service scenario but checks both important and disposable video packets are dropped equally in congestion. This case instead needs a gate for a single fifo queue holds both low-latency and bulk data traffic and evidence that voice packets experience controlled latency while bulk traffic retains available capacity.

B:

The proposed control is tied to the updated dscp-to-forwarding-class table misses the multicast source marking, typically observed when multicast video packets are assigned to the lowest-priority class after a classifier update. Here the target is no separate class queue protects delay-sensitive packets from serialization backlog; monitor voice packets experience controlled latency while bulk traffic retains available capacity.

D:

This gate monitors a different failure, the 802.1p priority observed downstream no longer matches the agreed enterprise service class. It would not detect the current problem: A single FIFO queue holds both low-latency and bulk data traffic. The appropriate check requires voice packets experience controlled latency while bulk traffic retains available capacity.

Question 429

An operator changes the outer VLAN priority marking at a PE. Observed: The 802.1p priority observed downstream no longer matches the agreed enterprise service class. Which targeted remediation is most appropriate for the observed condition?

  1. Attach a coherent 802.1p rewrite policy for supported tagged egress frames.
  2. Restrict the matching filter term to the authorized customer or logical interface.
  3. Apply equivalent scoped classification filters to both intended ingress interfaces.
  4. Move the rewrite policy to the actual egress logical interface with scoped review.

Explanation

Correct Answer

A:

This fix addresses the stated cause rather than an unrelated protocol. The reported symptom—The 802.1p priority observed downstream no longer matches the agreed enterprise service class—is consistent with an egress ieee 802.1p rewrite map is absent or maps the wrong forwarding class. Use the specified correction, then verify: Downstream tag captures show the intended priority codepoint values. Preserve existing policy and tenant isolation.

Incorrect Answers

B:

This change belongs to a different Class of Service (CoS) issue: A broad policer reduces throughput for other tenants on the same interface. That issue involves the policer was attached to a shared filter term rather than the customer's scoped traffic. The current symptom is The 802.1p priority observed downstream no longer matches the agreed enterprise service class. It instead requires attach a coherent 802.1p rewrite policy for supported tagged egress frames.

C:

The option may be useful when traffic is classified correctly only on one interface even though both see identical flows, but that is not the current evidence. Here, the 802.1p priority observed downstream no longer matches the agreed enterprise service class, indicating an egress ieee 802.1p rewrite map is absent or maps the wrong forwarding class. The targeted action is Attach a coherent 802.1p rewrite policy for supported tagged egress frames.

D:

This remediates the rewrite rule was bound to an interface with the wrong outbound direction, normally indicated by Downstream peers see markings unchanged while reverse traffic is altered unexpectedly. It would leave the observed problem (The 802.1p priority observed downstream no longer matches the agreed enterprise service class) unresolved. Address it with attach a coherent 802.1p rewrite policy for supported tagged egress frames.

Question 430

An operator changes the outer VLAN priority marking at a PE. Observed: The 802.1p priority observed downstream no longer matches the agreed enterprise service class. What evidence would validate recovery from this precise failure mode?

  1. Test packets on intended egress show correct markings and reverse traffic remains unchanged.
  2. Only the target guest class is capped while unrelated tenants keep their service rate.
  3. Matching application flows receive the same forwarding class regardless of incoming port.
  4. Downstream tag captures show the intended priority codepoint values.

Explanation

Correct Answer

D:

The intended result is Downstream tag captures show the intended priority codepoint values. It specifically verifies recovery from an egress ieee 802.1p rewrite map is absent or maps the wrong forwarding class, which produced the original symptom: The 802.1p priority observed downstream no longer matches the agreed enterprise service class. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

A:

This result is useful in another case with evidence Downstream peers see markings unchanged while reverse traffic is altered unexpectedly. It does not test recovery from the 802.1p priority observed downstream no longer matches the agreed enterprise service class. Check instead whether downstream tag captures show the intended priority codepoint values.

B:

It confirms an unrelated service correction: The policer was attached to a shared filter term rather than the customer's scoped traffic. The present case reports The 802.1p priority observed downstream no longer matches the agreed enterprise service class. Its completion test is Downstream tag captures show the intended priority codepoint values.

C:

That observation would verify a separate fault involving the firewall filter class action is attached on one ingress path but not the other. Its symptom is Traffic is classified correctly only on one interface even though both see identical flows. For this case the actual issue is an egress ieee 802.1p rewrite map is absent or maps the wrong forwarding class, and the relevant success signal is Downstream tag captures show the intended priority codepoint values.

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