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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 14

Question 130

An L1/L2 IS-IS PE imports customer prefixes from Level 2. Observed: A Level 1 access router never learns a required remote subnet. What evidence would validate recovery from this precise failure mode?

  1. Neighbors stay up and authentication errors stop in protocol logs.
  2. The allowed prefix reaches Level 1 without route feedback into Level 2.
  3. LSP IDs are unique and topology information becomes stable.
  4. Branch default chooses the planned reachable gateway and avoids unexpected detours.

Explanation

Correct Answer

B:

The intended result is The allowed prefix reaches Level 1 without route feedback into Level 2. It specifically verifies recovery from controlled l2-to-l1 route leaking is not configured for the permitted destination, which produced the original symptom: A Level 1 access router never learns a required remote subnet. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

A:

It confirms an unrelated service correction: Authentication method and key match do not agree between adjacent peers. The present case reports A Level 1 access router never learns a required remote subnet. Its completion test is The allowed prefix reaches Level 1 without route feedback into Level 2.

C:

This result is useful in another case with evidence The LSDB shows a second device's LSP under an existing system ID. It does not test recovery from a level 1 access router never learns a required remote subnet. Check instead whether the allowed prefix reaches Level 1 without route feedback into Level 2.

D:

That observation would verify a separate fault involving attached-bit and default-cost selection ignore intended internal metric planning. Its symptom is Traffic consistently uses the farther gateway despite the closer one being healthy. For this case the actual issue is controlled l2-to-l1 route leaking is not configured for the permitted destination, and the relevant success signal is The allowed prefix reaches Level 1 without route feedback into Level 2.

Question 131

An L1/L2 IS-IS PE imports customer prefixes from Level 2. Observed: A Level 1 access router never learns a required remote subnet. What underlying protocol or service configuration problem best explains the evidence?

  1. Duplicate IS-IS system IDs cause LSP origin ambiguity.
  2. Attached-bit and default-cost selection ignore intended internal metric planning.
  3. Controlled L2-to-L1 route leaking is not configured for the permitted destination.
  4. Authentication method and key match do not agree between adjacent peers.

Explanation

Correct Answer

C:

Because a Level 1 access router never learns a required remote subnet, the likely cause is controlled l2-to-l1 route leaking is not configured for the permitted destination. It is testable: Add scoped route leaking with compatible up/down protection and routing policy. Expected follow-up: The allowed prefix reaches Level 1 without route feedback into Level 2.

Incorrect Answers

A:

That explanation fits another condition: The LSDB shows a second device's LSP under an existing system ID. The evidence here is A Level 1 access router never learns a required remote subnet. Its closer root cause is Controlled L2-to-L1 route leaking is not configured for the permitted destination.

B:

The stated cause is possible elsewhere but explains traffic consistently uses the farther gateway despite the closer one being healthy, not a level 1 access router never learns a required remote subnet. This incident is better attributed to controlled l2-to-l1 route leaking is not configured for the permitted destination.

D:

Authentication method and key match do not agree between adjacent peers. would normally be accompanied by adjacencies flap only when authentication is enabled. The observed symptom is different: A Level 1 access router never learns a required remote subnet. The likely cause is Controlled L2-to-L1 route leaking is not configured for the permitted destination.

Question 132

An L1/L2 IS-IS PE imports customer prefixes from Level 2. Observed: A Level 1 access router never learns a required remote subnet. Which ongoing validation gate would best detect a recurrence of this problem?

  1. For each approved related change, verify that neighbors stay up and authentication errors stop in protocol logs. Flag recurrence if adjacencies flap only when authentication is enabled.
  2. For each approved related change, verify that branch default chooses the planned reachable gateway and avoids unexpected detours. Flag recurrence if traffic consistently uses the farther gateway despite the closer one being healthy.
  3. For each approved related change, verify that lSP IDs are unique and topology information becomes stable. Flag recurrence if the LSDB shows a second device's LSP under an existing system ID.
  4. For each approved related change, verify that the allowed prefix reaches Level 1 without route feedback into Level 2. Flag recurrence if a Level 1 access router never learns a required remote subnet.

Explanation

Correct Answer

D:

A useful regression gate tests whether the allowed prefix reaches Level 1 without route feedback into Level 2 and alerts when a Level 1 access router never learns a required remote subnet. This directly checks the technical weakness: Controlled L2-to-L1 route leaking is not configured for the permitted destination. 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, adjacencies flap only when authentication is enabled. It would not detect the current problem: A Level 1 access router never learns a required remote subnet. The appropriate check requires the allowed prefix reaches Level 1 without route feedback into Level 2.

B:

The proposed control is tied to attached-bit and default-cost selection ignore intended internal metric planning, typically observed when traffic consistently uses the farther gateway despite the closer one being healthy. Here the target is controlled l2-to-l1 route leaking is not configured for the permitted destination; monitor the allowed prefix reaches Level 1 without route feedback into Level 2.

C:

It is valid for another service scenario but checks the lsdb shows a second device's lsp under an existing system id. This case instead needs a gate for a level 1 access router never learns a required remote subnet and evidence that the allowed prefix reaches Level 1 without route feedback into Level 2.

Question 133

An IS-IS network has two potential L1/L2 gateways. Observed: Traffic consistently uses the farther gateway despite the closer one being healthy. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships.
  2. Repair MTU consistency and test hello packet carriage before reestablishing adjacency.
  3. Align the intended L2-to-L1 leak policy and imported metric on selected gateways.
  4. Adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.

Explanation

Correct Answer

A:

The observed condition is Traffic consistently uses the farther gateway despite the closer one being healthy. That indicates attached-bit and default-cost selection ignore intended internal metric planning. Applying the proposed remedy directly changes that condition. A concrete completion check is: Branch default chooses the planned reachable gateway and avoids unexpected detours.

Incorrect Answers

B:

This remediates is-is hello packet padding exceeds one path's available frame size, normally indicated by Neighbor remains in initialization and three-way handshake does not complete. It would leave the observed problem (Traffic consistently uses the farther gateway despite the closer one being healthy) unresolved. Address it with inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships.

C:

The option may be useful when a critical prefix from Level 2 appears in one branch with a problematic metric, but that is not the current evidence. Here, traffic consistently uses the farther gateway despite the closer one being healthy, indicating attached-bit and default-cost selection ignore intended internal metric planning. The targeted action is Inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships.

D:

This change belongs to a different IS-IS issue: Several IS-IS devices omit recently advertised routes during peak growth. That issue involves lsp fragmentation and configured lsp size assumptions were not reviewed. The current symptom is Traffic consistently uses the farther gateway despite the closer one being healthy. It instead requires inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships.

Question 134

An IS-IS network has two potential L1/L2 gateways. Observed: Traffic consistently uses the farther gateway despite the closer one being healthy. After the correction, which result would most convincingly show that this fault is resolved?

  1. All required prefix TLVs appear across receiving LSDBs without LSP truncation.
  2. Branch default chooses the planned reachable gateway and avoids unexpected detours.
  3. Neighbor forms at the intended level without padding drops.
  4. The permitted branch route has stable and correct cost across the area.

Explanation

Correct Answer

B:

After inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships, inspect whether branch default chooses the planned reachable gateway and avoids unexpected detours. This closes the loop between the reported observation (Traffic consistently uses the farther gateway despite the closer one being healthy) and the underlying issue (Attached-bit and default-cost selection ignore intended internal metric planning).

Incorrect Answers

A:

It confirms an unrelated service correction: LSP fragmentation and configured LSP size assumptions were not reviewed. The present case reports Traffic consistently uses the farther gateway despite the closer one being healthy. Its completion test is Branch default chooses the planned reachable gateway and avoids unexpected detours.

C:

This result is useful in another case with evidence Neighbor remains in initialization and three-way handshake does not complete. It does not test recovery from traffic consistently uses the farther gateway despite the closer one being healthy. Check instead whether branch default chooses the planned reachable gateway and avoids unexpected detours.

D:

That observation would verify a separate fault involving route leaking policy and metric adjustment are inconsistent among l1/l2 routers. Its symptom is A critical prefix from Level 2 appears in one branch with a problematic metric. For this case the actual issue is attached-bit and default-cost selection ignore intended internal metric planning, and the relevant success signal is Branch default chooses the planned reachable gateway and avoids unexpected detours.

Question 135

An IS-IS network has two potential L1/L2 gateways. Observed: Traffic consistently uses the farther gateway despite the closer one being healthy. Which root cause is most consistent with this symptom?

  1. IS-IS hello packet padding exceeds one path's available frame size.
  2. Attached-bit and default-cost selection ignore intended internal metric planning.
  3. LSP fragmentation and configured LSP size assumptions were not reviewed.
  4. Route leaking policy and metric adjustment are inconsistent among L1/L2 routers.

Explanation

Correct Answer

B:

The reported evidence—Traffic consistently uses the farther gateway despite the closer one being healthy—supports attached-bit and default-cost selection ignore intended internal metric planning. The appropriate intervention is to inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships, with confirmation from branch default chooses the planned reachable gateway and avoids unexpected detours. Other causes require actual device-state verification.

Incorrect Answers

A:

That explanation fits another condition: Neighbor remains in initialization and three-way handshake does not complete. The evidence here is Traffic consistently uses the farther gateway despite the closer one being healthy. Its closer root cause is Attached-bit and default-cost selection ignore intended internal metric planning.

C:

LSP fragmentation and configured LSP size assumptions were not reviewed. would normally be accompanied by several is-is devices omit recently advertised routes during peak growth. The observed symptom is different: Traffic consistently uses the farther gateway despite the closer one being healthy. The likely cause is Attached-bit and default-cost selection ignore intended internal metric planning.

D:

The stated cause is possible elsewhere but explains a critical prefix from level 2 appears in one branch with a problematic metric, not traffic consistently uses the farther gateway despite the closer one being healthy. This incident is better attributed to attached-bit and default-cost selection ignore intended internal metric planning.

Question 136

An IS-IS network has two potential L1/L2 gateways. Observed: Traffic consistently uses the farther gateway despite the closer one being healthy. Which change-acceptance control is most relevant to preventing this exact failure?

  1. For each approved related change, verify that neighbor forms at the intended level without padding drops. Flag recurrence if neighbor remains in initialization and three-way handshake does not complete.
  2. For each approved related change, verify that the permitted branch route has stable and correct cost across the area. Flag recurrence if a critical prefix from Level 2 appears in one branch with a problematic metric.
  3. For each approved related change, verify that all required prefix TLVs appear across receiving LSDBs without LSP truncation. Flag recurrence if several IS-IS devices omit recently advertised routes during peak growth.
  4. For each approved related change, verify that branch default chooses the planned reachable gateway and avoids unexpected detours. Flag recurrence if traffic consistently uses the farther gateway despite the closer one being healthy.

Explanation

Correct Answer

D:

The control is specific to the initial failure. It requires the result Branch default chooses the planned reachable gateway and avoids unexpected detours. and treats Traffic consistently uses the farther gateway despite the closer one being healthy. as a failure signal. The causal concern is attached-bit and default-cost selection ignore intended internal metric planning.

Incorrect Answers

A:

It is valid for another service scenario but checks neighbor remains in initialization and three-way handshake does not complete. This case instead needs a gate for traffic consistently uses the farther gateway despite the closer one being healthy and evidence that branch default chooses the planned reachable gateway and avoids unexpected detours.

B:

The proposed control is tied to route leaking policy and metric adjustment are inconsistent among l1/l2 routers, typically observed when a critical prefix from Level 2 appears in one branch with a problematic metric. Here the target is attached-bit and default-cost selection ignore intended internal metric planning; monitor branch default chooses the planned reachable gateway and avoids unexpected detours.

C:

This gate monitors a different failure, several is-is devices omit recently advertised routes during peak growth. It would not detect the current problem: Traffic consistently uses the farther gateway despite the closer one being healthy. The appropriate check requires branch default chooses the planned reachable gateway and avoids unexpected detours.

Question 137

An IS-IS transit segment runs on links with inconsistent physical MTUs. Observed: Neighbor remains in initialization and three-way handshake does not complete. What should the routing engineer change first to address this particular symptom?

  1. Repair MTU consistency and test hello packet carriage before reestablishing adjacency.
  2. Enable a valid Level 2 topology at the interarea boundary.
  3. Enable supported IS-IS IPv6 reachability on required interfaces and levels.
  4. Check equal accumulated IS-IS costs and supported ECMP settings.

Explanation

Correct Answer

A:

The decisive evidence is that Neighbor remains in initialization and three-way handshake does not complete. This follows from is-is hello packet padding exceeds one path's available frame size. The focused remedy is to repair MTU consistency and test hello packet carriage before reestablishing adjacency. Confirm improvement when neighbor forms at the intended level without padding drops. Validate on an approved lab or change window before touching production.

Incorrect Answers

B:

This change belongs to a different IS-IS issue: Transit prefixes in one area disappear from an adjacent area. That issue involves a router operates only level 1 across a segment requiring level 2 connectivity. The current symptom is Neighbor remains in initialization and three-way handshake does not complete. It instead requires repair MTU consistency and test hello packet carriage before reestablishing adjacency.

C:

The option may be useful when routers do not install IPv6 interrouter loopback prefixes, but that is not the current evidence. Here, neighbor remains in initialization and three-way handshake does not complete, indicating is-is hello packet padding exceeds one path's available frame size. The targeted action is Repair MTU consistency and test hello packet carriage before reestablishing adjacency.

D:

This remediates wide metrics differ or the installed multipath limit excludes an otherwise equal path, normally indicated by The backup next hop is not in the routing table despite physical path diversity. It would leave the observed problem (Neighbor remains in initialization and three-way handshake does not complete) unresolved. Address it with repair MTU consistency and test hello packet carriage before reestablishing adjacency.

Question 138

An IS-IS transit segment runs on links with inconsistent physical MTUs. Observed: Neighbor remains in initialization and three-way handshake does not complete. Which acceptance observation best confirms that the proposed change worked?

  1. The target IPv6 loopbacks install with correct IS-IS next hops.
  2. Both approved next hops appear with safe load distribution and failover.
  3. Remote Level 2 routes are reachable without improperly merging Level 1 areas.
  4. Neighbor forms at the intended level without padding drops.

Explanation

Correct Answer

D:

This acceptance criterion tests the actual fault. The source evidence was Neighbor remains in initialization and three-way handshake does not complete. The correction addresses is-is hello packet padding exceeds one path's available frame size; success requires neighbor forms at the intended level without padding drops.

Incorrect Answers

A:

That observation would verify a separate fault involving ipv6 topology or address-family advertisements are not enabled as intended. Its symptom is Routers do not install IPv6 interrouter loopback prefixes. For this case the actual issue is is-is hello packet padding exceeds one path's available frame size, and the relevant success signal is Neighbor forms at the intended level without padding drops.

B:

This result is useful in another case with evidence The backup next hop is not in the routing table despite physical path diversity. It does not test recovery from neighbor remains in initialization and three-way handshake does not complete. Check instead whether neighbor forms at the intended level without padding drops.

C:

It confirms an unrelated service correction: A router operates only Level 1 across a segment requiring Level 2 connectivity. The present case reports Neighbor remains in initialization and three-way handshake does not complete. Its completion test is Neighbor forms at the intended level without padding drops.

Question 139

An IS-IS transit segment runs on links with inconsistent physical MTUs. Observed: Neighbor remains in initialization and three-way handshake does not complete. What is the most likely source of the observed routing or service failure?

  1. IS-IS hello packet padding exceeds one path's available frame size.
  2. IPv6 topology or address-family advertisements are not enabled as intended.
  3. A router operates only Level 1 across a segment requiring Level 2 connectivity.
  4. Wide metrics differ or the installed multipath limit excludes an otherwise equal path.

Explanation

Correct Answer

A:

This explanation is the closest match to the observed symptom: Neighbor remains in initialization and three-way handshake does not complete. The specified root issue is IS-IS hello packet padding exceeds one path's available frame size. Repair it through repair MTU consistency and test hello packet carriage before reestablishing adjacency, then check neighbor forms at the intended level without padding drops.

Incorrect Answers

B:

The stated cause is possible elsewhere but explains routers do not install ipv6 interrouter loopback prefixes, not neighbor remains in initialization and three-way handshake does not complete. This incident is better attributed to is-is hello packet padding exceeds one path's available frame size.

C:

A router operates only Level 1 across a segment requiring Level 2 connectivity. would normally be accompanied by transit prefixes in one area disappear from an adjacent area. The observed symptom is different: Neighbor remains in initialization and three-way handshake does not complete. The likely cause is IS-IS hello packet padding exceeds one path's available frame size.

D:

That explanation fits another condition: The backup next hop is not in the routing table despite physical path diversity. The evidence here is Neighbor remains in initialization and three-way handshake does not complete. Its closer root cause is IS-IS hello packet padding exceeds one path's available frame size.

Question 140

An IS-IS transit segment runs on links with inconsistent physical MTUs. Observed: Neighbor remains in initialization and three-way handshake does not complete. What operational check best guards against this problem returning?

  1. For each approved related change, verify that remote Level 2 routes are reachable without improperly merging Level 1 areas. Flag recurrence if transit prefixes in one area disappear from an adjacent area.
  2. For each approved related change, verify that both approved next hops appear with safe load distribution and failover. Flag recurrence if the backup next hop is not in the routing table despite physical path diversity.
  3. For each approved related change, verify that neighbor forms at the intended level without padding drops. Flag recurrence if neighbor remains in initialization and three-way handshake does not complete.
  4. For each approved related change, verify that the target IPv6 loopbacks install with correct IS-IS next hops. Flag recurrence if routers do not install IPv6 interrouter loopback prefixes.

Explanation

Correct Answer

C:

This control asks for the same recovery evidence (Neighbor forms at the intended level without padding drops) and flags recurrence of the same failure (Neighbor remains in initialization and three-way handshake does not complete). It targets the underlying issue, is-is hello packet padding exceeds one path's available frame size, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

This gate monitors a different failure, transit prefixes in one area disappear from an adjacent area. It would not detect the current problem: Neighbor remains in initialization and three-way handshake does not complete. The appropriate check requires neighbor forms at the intended level without padding drops.

B:

It is valid for another service scenario but checks the backup next hop is not in the routing table despite physical path diversity. This case instead needs a gate for neighbor remains in initialization and three-way handshake does not complete and evidence that neighbor forms at the intended level without padding drops.

D:

The proposed control is tied to ipv6 topology or address-family advertisements are not enabled as intended, typically observed when routers do not install IPv6 interrouter loopback prefixes. Here the target is is-is hello packet padding exceeds one path's available frame size; monitor neighbor forms at the intended level without padding drops.

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