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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 17

Question 160

A large IS-IS domain undergoes maintenance with rapidly flapping optical links. Observed: Repeated LSP floods overload route processors across the metro. Which change-acceptance control is most relevant to preventing this exact failure?

  1. 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.
  2. For each approved related change, verify that all devices agree on the LSP sequence and routing destinations become reachable. Flag recurrence if neighbors show Up but a route is transiently absent on one PE.
  3. For each approved related change, verify that all transit routes use the intended wide metric values with stable SPF outcomes. Flag recurrence if paths appear with maximum legacy metric rather than engineering cost.
  4. For each approved related change, verify that lSP churn declines while a legitimate failover still converges promptly. Flag recurrence if repeated LSP floods overload route processors across the metro.

Explanation

Correct Answer

D:

The control is specific to the initial failure. It requires the result LSP churn declines while a legitimate failover still converges promptly. and treats Repeated LSP floods overload route processors across the metro. as a failure signal. The causal concern is an unstable interface causes repeated topology regenerations and spf scheduling.

Incorrect Answers

A:

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 repeated lsp floods overload route processors across the metro and evidence that lSP churn declines while a legitimate failover still converges promptly.

B:

This gate monitors a different failure, neighbors show up but a route is transiently absent on one pe. It would not detect the current problem: Repeated LSP floods overload route processors across the metro. The appropriate check requires lSP churn declines while a legitimate failover still converges promptly.

C:

The proposed control is tied to one or more devices retain incompatible metric-style processing, typically observed when paths appear with maximum legacy metric rather than engineering cost. Here the target is an unstable interface causes repeated topology regenerations and spf scheduling; monitor lSP churn declines while a legitimate failover still converges promptly.

Question 161

An IS-IS router experiences adjacent system-ID collisions. Observed: The LSDB shows a second device's LSP under an existing system ID. What should the routing engineer change first to address this particular symptom?

  1. Add scoped route leaking with compatible up/down protection and routing policy.
  2. Assign unique NET system IDs and restart affected adjacencies safely.
  3. Adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.
  4. Stage matched IS-IS authentication keys and supported algorithm configuration.

Explanation

Correct Answer

B:

The decisive evidence is that The LSDB shows a second device's LSP under an existing system ID. This follows from duplicate is-is system ids cause lsp origin ambiguity. The focused remedy is to assign unique NET system IDs and restart affected adjacencies safely. Confirm improvement when lSP IDs are unique and topology information becomes stable. Validate on an approved lab or change window before touching production.

Incorrect Answers

A:

This remediates controlled l2-to-l1 route leaking is not configured for the permitted destination, normally indicated by A Level 1 access router never learns a required remote subnet. It would leave the observed problem (The LSDB shows a second device's LSP under an existing system ID) unresolved. Address it with assign unique NET system IDs and restart affected adjacencies safely.

C:

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 The LSDB shows a second device's LSP under an existing system ID. It instead requires assign unique NET system IDs and restart affected adjacencies safely.

D:

The option may be useful when adjacencies flap only when authentication is enabled, but that is not the current evidence. Here, the LSDB shows a second device's LSP under an existing system ID, indicating duplicate is-is system ids cause lsp origin ambiguity. The targeted action is Assign unique NET system IDs and restart affected adjacencies safely.

Question 162

An IS-IS router experiences adjacent system-ID collisions. Observed: The LSDB shows a second device's LSP under an existing system ID. Which acceptance observation best confirms that the proposed change worked?

  1. Neighbors stay up and authentication errors stop in protocol logs.
  2. All required prefix TLVs appear across receiving LSDBs without LSP truncation.
  3. The allowed prefix reaches Level 1 without route feedback into Level 2.
  4. LSP IDs are unique and topology information becomes stable.

Explanation

Correct Answer

D:

This acceptance criterion tests the actual fault. The source evidence was The LSDB shows a second device's LSP under an existing system ID. The correction addresses duplicate is-is system ids cause lsp origin ambiguity; success requires lSP IDs are unique and topology information becomes stable.

Incorrect Answers

A:

That observation would verify a separate fault involving authentication method and key match do not agree between adjacent peers. Its symptom is Adjacencies flap only when authentication is enabled. For this case the actual issue is duplicate is-is system ids cause lsp origin ambiguity, and the relevant success signal is LSP IDs are unique and topology information becomes stable.

B:

It confirms an unrelated service correction: LSP fragmentation and configured LSP size assumptions were not reviewed. The present case reports The LSDB shows a second device's LSP under an existing system ID. Its completion test is LSP IDs are unique and topology information becomes stable.

C:

This result is useful in another case with evidence A Level 1 access router never learns a required remote subnet. It does not test recovery from the lsdb shows a second device's lsp under an existing system id. Check instead whether lSP IDs are unique and topology information becomes stable.

Question 163

An IS-IS router experiences adjacent system-ID collisions. Observed: The LSDB shows a second device's LSP under an existing system ID. What is the most likely source of the observed routing or service failure?

  1. LSP fragmentation and configured LSP size assumptions were not reviewed.
  2. Duplicate IS-IS system IDs cause LSP origin ambiguity.
  3. Authentication method and key match do not agree between adjacent peers.
  4. Controlled L2-to-L1 route leaking is not configured for the permitted destination.

Explanation

Correct Answer

B:

This explanation is the closest match to the observed symptom: The LSDB shows a second device's LSP under an existing system ID. The specified root issue is Duplicate IS-IS system IDs cause LSP origin ambiguity. Repair it through assign unique NET system IDs and restart affected adjacencies safely, then check lSP IDs are unique and topology information becomes stable.

Incorrect Answers

A:

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: The LSDB shows a second device's LSP under an existing system ID. The likely cause is Duplicate IS-IS system IDs cause LSP origin ambiguity.

C:

The stated cause is possible elsewhere but explains adjacencies flap only when authentication is enabled, not the lsdb shows a second device's lsp under an existing system id. This incident is better attributed to duplicate is-is system ids cause lsp origin ambiguity.

D:

That explanation fits another condition: A Level 1 access router never learns a required remote subnet. The evidence here is The LSDB shows a second device's LSP under an existing system ID. Its closer root cause is Duplicate IS-IS system IDs cause LSP origin ambiguity.

Question 164

An IS-IS router experiences adjacent system-ID collisions. Observed: The LSDB shows a second device's LSP under an existing system ID. What operational check best guards against this problem returning?

  1. 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.
  2. 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.
  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

C:

This control asks for the same recovery evidence (LSP IDs are unique and topology information becomes stable) and flags recurrence of the same failure (The LSDB shows a second device's LSP under an existing system ID). It targets the underlying issue, duplicate is-is system ids cause lsp origin ambiguity, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

This gate monitors a different failure, several is-is devices omit recently advertised routes during peak growth. It would not detect the current problem: The LSDB shows a second device's LSP under an existing system ID. The appropriate check requires lSP IDs are unique and topology information becomes stable.

B:

The proposed control is tied to authentication method and key match do not agree between adjacent peers, typically observed when adjacencies flap only when authentication is enabled. Here the target is duplicate is-is system ids cause lsp origin ambiguity; monitor lSP IDs are unique and topology information becomes stable.

D:

It is valid for another service scenario but checks a level 1 access router never learns a required remote subnet. This case instead needs a gate for the lsdb shows a second device's lsp under an existing system id and evidence that lSP IDs are unique and topology information becomes stable.

Question 165

A service-provider core receives LSPs close to the configured database size. Observed: Several IS-IS devices omit recently advertised routes during peak growth. Which targeted remediation is most appropriate for the observed condition?

  1. Align the intended L2-to-L1 leak policy and imported metric on selected gateways.
  2. Adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.
  3. Enable supported IS-IS IPv6 reachability on required interfaces and levels.
  4. Inspect gateway attached-bit advertisement and set appropriate level-1 metric relationships.

Explanation

Correct Answer

B:

This fix addresses the stated cause rather than an unrelated protocol. The reported symptom—Several IS-IS devices omit recently advertised routes during peak growth—is consistent with lsp fragmentation and configured lsp size assumptions were not reviewed. Use the specified correction, then verify: All required prefix TLVs appear across receiving LSDBs without LSP truncation. Preserve existing policy and tenant isolation.

Incorrect Answers

A:

This remediates route leaking policy and metric adjustment are inconsistent among l1/l2 routers, normally indicated by A critical prefix from Level 2 appears in one branch with a problematic metric. It would leave the observed problem (Several IS-IS devices omit recently advertised routes during peak growth) unresolved. Address it with adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.

C:

The option may be useful when routers do not install IPv6 interrouter loopback prefixes, but that is not the current evidence. Here, several IS-IS devices omit recently advertised routes during peak growth, indicating lsp fragmentation and configured lsp size assumptions were not reviewed. The targeted action is Adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.

D:

This change belongs to a different IS-IS issue: Traffic consistently uses the farther gateway despite the closer one being healthy. That issue involves attached-bit and default-cost selection ignore intended internal metric planning. The current symptom is Several IS-IS devices omit recently advertised routes during peak growth. It instead requires adjust supported LSP capacity and fragmentation settings with MTU compatibility checks.

Question 166

A service-provider core receives LSPs close to the configured database size. Observed: Several IS-IS devices omit recently advertised routes during peak growth. What evidence would validate recovery from this precise failure mode?

  1. Branch default chooses the planned reachable gateway and avoids unexpected detours.
  2. The target IPv6 loopbacks install with correct IS-IS next hops.
  3. All required prefix TLVs appear across receiving LSDBs without LSP truncation.
  4. The permitted branch route has stable and correct cost across the area.

Explanation

Correct Answer

C:

The intended result is All required prefix TLVs appear across receiving LSDBs without LSP truncation. It specifically verifies recovery from lsp fragmentation and configured lsp size assumptions were not reviewed, which produced the original symptom: Several IS-IS devices omit recently advertised routes during peak growth. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

A:

It confirms an unrelated service correction: Attached-bit and default-cost selection ignore intended internal metric planning. The present case reports Several IS-IS devices omit recently advertised routes during peak growth. Its completion test is All required prefix TLVs appear across receiving LSDBs without LSP truncation.

B:

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 lsp fragmentation and configured lsp size assumptions were not reviewed, and the relevant success signal is All required prefix TLVs appear across receiving LSDBs without LSP truncation.

D:

This result is useful in another case with evidence A critical prefix from Level 2 appears in one branch with a problematic metric. It does not test recovery from several is-is devices omit recently advertised routes during peak growth. Check instead whether all required prefix TLVs appear across receiving LSDBs without LSP truncation.

Question 167

A service-provider core receives LSPs close to the configured database size. Observed: Several IS-IS devices omit recently advertised routes during peak growth. What underlying protocol or service configuration problem best explains the evidence?

  1. Route leaking policy and metric adjustment are inconsistent among L1/L2 routers.
  2. IPv6 topology or address-family advertisements are not enabled as intended.
  3. Attached-bit and default-cost selection ignore intended internal metric planning.
  4. LSP fragmentation and configured LSP size assumptions were not reviewed.

Explanation

Correct Answer

D:

Because several IS-IS devices omit recently advertised routes during peak growth, the likely cause is lsp fragmentation and configured lsp size assumptions were not reviewed. It is testable: Adjust supported LSP capacity and fragmentation settings with MTU compatibility checks. Expected follow-up: All required prefix TLVs appear across receiving LSDBs without LSP truncation.

Incorrect Answers

A:

That explanation fits another condition: A critical prefix from Level 2 appears in one branch with a problematic metric. The evidence here is Several IS-IS devices omit recently advertised routes during peak growth. Its closer root cause is LSP fragmentation and configured LSP size assumptions were not reviewed.

B:

The stated cause is possible elsewhere but explains routers do not install ipv6 interrouter loopback prefixes, not several is-is devices omit recently advertised routes during peak growth. This incident is better attributed to lsp fragmentation and configured lsp size assumptions were not reviewed.

C:

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

Question 168

A service-provider core receives LSPs close to the configured database size. Observed: Several IS-IS devices omit recently advertised routes during peak growth. Which ongoing validation gate would best detect a recurrence of this problem?

  1. 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.
  2. 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.
  3. 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.
  4. 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.

Explanation

Correct Answer

D:

A useful regression gate tests whether all required prefix TLVs appear across receiving LSDBs without LSP truncation and alerts when several IS-IS devices omit recently advertised routes during peak growth. This directly checks the technical weakness: LSP fragmentation and configured LSP size assumptions were not reviewed. 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 consistently uses the farther gateway despite the closer one being healthy. It would not detect the current problem: Several IS-IS devices omit recently advertised routes during peak growth. The appropriate check requires all required prefix TLVs appear across receiving LSDBs without LSP truncation.

B:

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 lsp fragmentation and configured lsp size assumptions were not reviewed; monitor all required prefix TLVs appear across receiving LSDBs without LSP truncation.

C:

It is valid for another service scenario but checks a critical prefix from level 2 appears in one branch with a problematic metric. This case instead needs a gate for several is-is devices omit recently advertised routes during peak growth and evidence that all required prefix TLVs appear across receiving LSDBs without LSP truncation.

Question 169

An IPv6 IS-IS deployment has working IPv4 reachability. Observed: Routers do not install IPv6 interrouter loopback prefixes. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Make the customer network passive or remove protocol participation as appropriate.
  2. Enable supported IS-IS IPv6 reachability on required interfaces and levels.
  3. Repair MTU consistency and test hello packet carriage before reestablishing adjacency.
  4. Check equal accumulated IS-IS costs and supported ECMP settings.

Explanation

Correct Answer

B:

The observed condition is Routers do not install IPv6 interrouter loopback prefixes. That indicates ipv6 topology or address-family advertisements are not enabled as intended. Applying the proposed remedy directly changes that condition. A concrete completion check is: The target IPv6 loopbacks install with correct IS-IS next hops.

Incorrect Answers

A:

This remediates the customer interface was enabled as an active is-is circuit instead of a passive advertisement, normally indicated by Customer service interface accidentally forms an IS-IS adjacency. It would leave the observed problem (Routers do not install IPv6 interrouter loopback prefixes) unresolved. Address it with enable supported IS-IS IPv6 reachability on required interfaces and levels.

C:

The option may be useful when neighbor remains in initialization and three-way handshake does not complete, but that is not the current evidence. Here, routers do not install IPv6 interrouter loopback prefixes, indicating ipv6 topology or address-family advertisements are not enabled as intended. The targeted action is Enable supported IS-IS IPv6 reachability on required interfaces and levels.

D:

This change belongs to a different IS-IS issue: The backup next hop is not in the routing table despite physical path diversity. That issue involves wide metrics differ or the installed multipath limit excludes an otherwise equal path. The current symptom is Routers do not install IPv6 interrouter loopback prefixes. It instead requires enable supported IS-IS IPv6 reachability on required interfaces and levels.

Question 170

An IPv6 IS-IS deployment has working IPv4 reachability. Observed: Routers do not install IPv6 interrouter loopback prefixes. After the correction, which result would most convincingly show that this fault is resolved?

  1. The target IPv6 loopbacks install with correct IS-IS next hops.
  2. No customer-facing IS-IS Hello forms a neighbor while internal routing remains correct.
  3. Neighbor forms at the intended level without padding drops.
  4. Both approved next hops appear with safe load distribution and failover.

Explanation

Correct Answer

A:

After enable supported IS-IS IPv6 reachability on required interfaces and levels, inspect whether the target IPv6 loopbacks install with correct IS-IS next hops. This closes the loop between the reported observation (Routers do not install IPv6 interrouter loopback prefixes) and the underlying issue (IPv6 topology or address-family advertisements are not enabled as intended).

Incorrect Answers

B:

This result is useful in another case with evidence Customer service interface accidentally forms an IS-IS adjacency. It does not test recovery from routers do not install ipv6 interrouter loopback prefixes. Check instead whether the target IPv6 loopbacks install with correct IS-IS next hops.

C:

That observation would verify a separate fault involving is-is hello packet padding exceeds one path's available frame size. Its symptom is Neighbor remains in initialization and three-way handshake does not complete. For this case the actual issue is ipv6 topology or address-family advertisements are not enabled as intended, and the relevant success signal is The target IPv6 loopbacks install with correct IS-IS next hops.

D:

It confirms an unrelated service correction: Wide metrics differ or the installed multipath limit excludes an otherwise equal path. The present case reports Routers do not install IPv6 interrouter loopback prefixes. Its completion test is The target IPv6 loopbacks install with correct IS-IS next hops.

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