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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 26

Question 250

An operator attaches a standard BGP community to customer routes. Observed: The upstream does not apply the agreed blackhole policy. What evidence would validate recovery from this precise failure mode?

  1. The session's TCP endpoint addresses match the planned loopback addresses.
  2. Reflected route attributes remain loop-free and no repeated re-advertisement occurs.
  3. The upstream confirms the intended tagged route receives the agreed action.
  4. The receiver sees the complete three-part community and classifies it correctly.

Explanation

Correct Answer

C:

The intended result is The upstream confirms the intended tagged route receives the agreed action. It specifically verifies recovery from the carrier expects a different community value or route export suppresses communities, which produced the original symptom: The upstream does not apply the agreed blackhole policy. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

A:

This result is useful in another case with evidence One router silently sources TCP from a physical interface instead of its loopback. It does not test recovery from the upstream does not apply the agreed blackhole policy. Check instead whether the upstream confirms the intended tagged route receives the agreed action.

B:

It confirms an unrelated service correction: Client and nonclient relationships were modified without controlling reflection loops. The present case reports The upstream does not apply the agreed blackhole policy. Its completion test is The upstream confirms the intended tagged route receives the agreed action.

D:

That observation would verify a separate fault involving standard communities do not provide the three-field large-community semantics. Its symptom is A 32-bit community representation cannot encode the required triple of values. For this case the actual issue is the carrier expects a different community value or route export suppresses communities, and the relevant success signal is The upstream confirms the intended tagged route receives the agreed action.

Question 251

An operator attaches a standard BGP community to customer routes. Observed: The upstream does not apply the agreed blackhole policy. What underlying protocol or service configuration problem best explains the evidence?

  1. Standard communities do not provide the three-field large-community semantics.
  2. The carrier expects a different community value or route export suppresses communities.
  3. Update-source and reachability design disagree across the peers.
  4. Client and nonclient relationships were modified without controlling reflection loops.

Explanation

Correct Answer

B:

Because the upstream does not apply the agreed blackhole policy, the likely cause is the carrier expects a different community value or route export suppresses communities. It is testable: Use the contracted community value and enable the permitted community propagation. Expected follow-up: The upstream confirms the intended tagged route receives the agreed action.

Incorrect Answers

A:

The stated cause is possible elsewhere but explains a 32-bit community representation cannot encode the required triple of values, not the upstream does not apply the agreed blackhole policy. This incident is better attributed to the carrier expects a different community value or route export suppresses communities.

C:

That explanation fits another condition: One router silently sources TCP from a physical interface instead of its loopback. The evidence here is The upstream does not apply the agreed blackhole policy. Its closer root cause is The carrier expects a different community value or route export suppresses communities.

D:

Client and nonclient relationships were modified without controlling reflection loops. would normally be accompanied by path oscillation appears between two route reflectors after clients are rearranged. The observed symptom is different: The upstream does not apply the agreed blackhole policy. The likely cause is The carrier expects a different community value or route export suppresses communities.

Question 252

An operator attaches a standard BGP community to customer routes. Observed: The upstream does not apply the agreed blackhole policy. Which ongoing validation gate would best detect a recurrence of this problem?

  1. For each approved related change, verify that the receiver sees the complete three-part community and classifies it correctly. Flag recurrence if a 32-bit community representation cannot encode the required triple of values.
  2. For each approved related change, verify that the upstream confirms the intended tagged route receives the agreed action. Flag recurrence if the upstream does not apply the agreed blackhole policy.
  3. For each approved related change, verify that reflected route attributes remain loop-free and no repeated re-advertisement occurs. Flag recurrence if path oscillation appears between two route reflectors after clients are rearranged.
  4. For each approved related change, verify that the session's TCP endpoint addresses match the planned loopback addresses. Flag recurrence if one router silently sources TCP from a physical interface instead of its loopback.

Explanation

Correct Answer

B:

A useful regression gate tests whether the upstream confirms the intended tagged route receives the agreed action and alerts when the upstream does not apply the agreed blackhole policy. This directly checks the technical weakness: The carrier expects a different community value or route export suppresses communities. The gate is derived from the fictional incident and is not an independent Juniper engineer signoff.

Incorrect Answers

A:

The proposed control is tied to standard communities do not provide the three-field large-community semantics, typically observed when a 32-bit community representation cannot encode the required triple of values. Here the target is the carrier expects a different community value or route export suppresses communities; monitor the upstream confirms the intended tagged route receives the agreed action.

C:

This gate monitors a different failure, path oscillation appears between two route reflectors after clients are rearranged. It would not detect the current problem: The upstream does not apply the agreed blackhole policy. The appropriate check requires the upstream confirms the intended tagged route receives the agreed action.

D:

It is valid for another service scenario but checks one router silently sources tcp from a physical interface instead of its loopback. This case instead needs a gate for the upstream does not apply the agreed blackhole policy and evidence that the upstream confirms the intended tagged route receives the agreed action.

Question 253

A customer is moving to large BGP communities for policy scaling. Observed: A 32-bit community representation cannot encode the required triple of values. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Use supported large-community attributes and matching import/export policy.
  2. Align route-policy characteristics and supported internal multipath behavior.
  3. Rewrite and test the policy expression against permitted and blocked AS paths.
  4. Evaluate Junos BGP attributes and policy ordering rather than importing another vendor's model.

Explanation

Correct Answer

A:

The observed condition is A 32-bit community representation cannot encode the required triple of values. That indicates standard communities do not provide the three-field large-community semantics. Applying the proposed remedy directly changes that condition. A concrete completion check is: The receiver sees the complete three-part community and classifies it correctly.

Incorrect Answers

B:

The option may be useful when equal NLRI from different originators causes inconsistent distribution, but that is not the current evidence. Here, a 32-bit community representation cannot encode the required triple of values, indicating standard communities do not provide the three-field large-community semantics. The targeted action is Use supported large-community attributes and matching import/export policy.

C:

This remediates the regex was not anchored to the intended as path boundaries, normally indicated by The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. It would leave the observed problem (A 32-bit community representation cannot encode the required triple of values) unresolved. Address it with use supported large-community attributes and matching import/export policy.

D:

This change belongs to a different BGP issue: An operator assumes weight should decide the path on a Junos router. That issue involves vendor-specific nonportable bgp weight behavior was conflated with junos route preference. The current symptom is A 32-bit community representation cannot encode the required triple of values. It instead requires use supported large-community attributes and matching import/export policy.

Question 254

A customer is moving to large BGP communities for policy scaling. Observed: A 32-bit community representation cannot encode the required triple of values. After the correction, which result would most convincingly show that this fault is resolved?

  1. Only the intended AS-path patterns trigger the route filter.
  2. The receiver sees the complete three-part community and classifies it correctly.
  3. Both permitted paths become active only when their attributes qualify.
  4. The selected best path matches valid Junos preference and BGP decision rules.

Explanation

Correct Answer

B:

After use supported large-community attributes and matching import/export policy, inspect whether the receiver sees the complete three-part community and classifies it correctly. This closes the loop between the reported observation (A 32-bit community representation cannot encode the required triple of values) and the underlying issue (Standard communities do not provide the three-field large-community semantics).

Incorrect Answers

A:

This result is useful in another case with evidence The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. It does not test recovery from a 32-bit community representation cannot encode the required triple of values. Check instead whether the receiver sees the complete three-part community and classifies it correctly.

C:

That observation would verify a separate fault involving required bgp multipath attributes are not sufficiently equivalent for multipath. Its symptom is Equal NLRI from different originators causes inconsistent distribution. For this case the actual issue is standard communities do not provide the three-field large-community semantics, and the relevant success signal is The receiver sees the complete three-part community and classifies it correctly.

D:

It confirms an unrelated service correction: Vendor-specific nonportable BGP weight behavior was conflated with Junos route preference. The present case reports A 32-bit community representation cannot encode the required triple of values. Its completion test is The receiver sees the complete three-part community and classifies it correctly.

Question 255

A customer is moving to large BGP communities for policy scaling. Observed: A 32-bit community representation cannot encode the required triple of values. Which root cause is most consistent with this symptom?

  1. Required BGP multipath attributes are not sufficiently equivalent for multipath.
  2. Standard communities do not provide the three-field large-community semantics.
  3. Vendor-specific nonportable BGP weight behavior was conflated with Junos route preference.
  4. The regex was not anchored to the intended AS path boundaries.

Explanation

Correct Answer

B:

The reported evidence—A 32-bit community representation cannot encode the required triple of values—supports standard communities do not provide the three-field large-community semantics. The appropriate intervention is to use supported large-community attributes and matching import/export policy, with confirmation from the receiver sees the complete three-part community and classifies it correctly. Other causes require actual device-state verification.

Incorrect Answers

A:

The stated cause is possible elsewhere but explains equal nlri from different originators causes inconsistent distribution, not a 32-bit community representation cannot encode the required triple of values. This incident is better attributed to standard communities do not provide the three-field large-community semantics.

C:

Vendor-specific nonportable BGP weight behavior was conflated with Junos route preference. would normally be accompanied by an operator assumes weight should decide the path on a junos router. The observed symptom is different: A 32-bit community representation cannot encode the required triple of values. The likely cause is Standard communities do not provide the three-field large-community semantics.

D:

That explanation fits another condition: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. The evidence here is A 32-bit community representation cannot encode the required triple of values. Its closer root cause is Standard communities do not provide the three-field large-community semantics.

Question 256

A customer is moving to large BGP communities for policy scaling. Observed: A 32-bit community representation cannot encode the required triple of values. Which change-acceptance control is most relevant to preventing this exact failure?

  1. For each approved related change, verify that the selected best path matches valid Junos preference and BGP decision rules. Flag recurrence if an operator assumes weight should decide the path on a Junos router.
  2. For each approved related change, verify that only the intended AS-path patterns trigger the route filter. Flag recurrence if the filter matches unrelated longer AS-path sequences and rejects legitimate traffic.
  3. For each approved related change, verify that the receiver sees the complete three-part community and classifies it correctly. Flag recurrence if a 32-bit community representation cannot encode the required triple of values.
  4. For each approved related change, verify that both permitted paths become active only when their attributes qualify. Flag recurrence if equal NLRI from different originators causes inconsistent distribution.

Explanation

Correct Answer

C:

The control is specific to the initial failure. It requires the result The receiver sees the complete three-part community and classifies it correctly. and treats A 32-bit community representation cannot encode the required triple of values. as a failure signal. The causal concern is standard communities do not provide the three-field large-community semantics.

Incorrect Answers

A:

This gate monitors a different failure, an operator assumes weight should decide the path on a junos router. It would not detect the current problem: A 32-bit community representation cannot encode the required triple of values. The appropriate check requires the receiver sees the complete three-part community and classifies it correctly.

B:

It is valid for another service scenario but checks the filter matches unrelated longer as-path sequences and rejects legitimate traffic. This case instead needs a gate for a 32-bit community representation cannot encode the required triple of values and evidence that the receiver sees the complete three-part community and classifies it correctly.

D:

The proposed control is tied to required bgp multipath attributes are not sufficiently equivalent for multipath, typically observed when equal NLRI from different originators causes inconsistent distribution. Here the target is standard communities do not provide the three-field large-community semantics; monitor the receiver sees the complete three-part community and classifies it correctly.

Question 257

A BGP import filter includes a regular expression for customer AS paths. Observed: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. What should the routing engineer change first to address this particular symptom?

  1. Remove the accidental AS-path loop or redesign the session without broad allow-as loops.
  2. Enable the intended multiprotocol IPv6 unicast family on both neighbors.
  3. Rewrite and test the policy expression against permitted and blocked AS paths.
  4. Restrict the MED mutation term to the agreed prefixes and peer communities.

Explanation

Correct Answer

C:

The decisive evidence is that The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. This follows from the regex was not anchored to the intended as path boundaries. The focused remedy is to rewrite and test the policy expression against permitted and blocked AS paths. Confirm improvement when only the intended AS-path patterns trigger the route filter. Validate on an approved lab or change window before touching production.

Incorrect Answers

A:

The option may be useful when the next router drops it because its own AS is present in the path, but that is not the current evidence. Here, the filter matches unrelated longer AS-path sequences and rejects legitimate traffic, indicating the regex was not anchored to the intended as path boundaries. The targeted action is Rewrite and test the policy expression against permitted and blocked AS paths.

B:

This change belongs to a different BGP issue: The IPv4 BGP session is Established but IPv6 route exchange never starts. That issue involves ipv6 address-family activation is missing for that neighbor. The current symptom is The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. It instead requires rewrite and test the policy expression against permitted and blocked AS paths.

D:

This remediates a broad routing-policy term matches routes outside its intended customer prefix list, normally indicated by Policy unexpectedly modifies MED for every customer route. It would leave the observed problem (The filter matches unrelated longer AS-path sequences and rejects legitimate traffic) unresolved. Address it with rewrite and test the policy expression against permitted and blocked AS paths.

Question 258

A BGP import filter includes a regular expression for customer AS paths. Observed: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. Which acceptance observation best confirms that the proposed change worked?

  1. An authorized loop-free path is accepted and no repeated AS numbers cause rejection.
  2. IPv6 NLRI appears with reachable IPv6 next hops while IPv4 remains stable.
  3. Only the intended AS-path patterns trigger the route filter.
  4. MED differs only on targeted routes and unrelated announcements remain unchanged.

Explanation

Correct Answer

C:

This acceptance criterion tests the actual fault. The source evidence was The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. The correction addresses the regex was not anchored to the intended as path boundaries; success requires only the intended AS-path patterns trigger the route filter.

Incorrect Answers

A:

That observation would verify a separate fault involving as-loop prevention correctly rejects a path containing the local autonomous system. Its symptom is The next router drops it because its own AS is present in the path. For this case the actual issue is the regex was not anchored to the intended as path boundaries, and the relevant success signal is Only the intended AS-path patterns trigger the route filter.

B:

It confirms an unrelated service correction: IPv6 address-family activation is missing for that neighbor. The present case reports The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. Its completion test is Only the intended AS-path patterns trigger the route filter.

D:

This result is useful in another case with evidence Policy unexpectedly modifies MED for every customer route. It does not test recovery from the filter matches unrelated longer as-path sequences and rejects legitimate traffic. Check instead whether only the intended AS-path patterns trigger the route filter.

Question 259

A BGP import filter includes a regular expression for customer AS paths. Observed: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. What is the most likely source of the observed routing or service failure?

  1. IPv6 address-family activation is missing for that neighbor.
  2. AS-loop prevention correctly rejects a path containing the local autonomous system.
  3. The regex was not anchored to the intended AS path boundaries.
  4. A broad routing-policy term matches routes outside its intended customer prefix list.

Explanation

Correct Answer

C:

This explanation is the closest match to the observed symptom: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. The specified root issue is The regex was not anchored to the intended AS path boundaries. Repair it through rewrite and test the policy expression against permitted and blocked AS paths, then check only the intended AS-path patterns trigger the route filter.

Incorrect Answers

A:

IPv6 address-family activation is missing for that neighbor. would normally be accompanied by the ipv4 bgp session is established but ipv6 route exchange never starts. The observed symptom is different: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. The likely cause is The regex was not anchored to the intended AS path boundaries.

B:

The stated cause is possible elsewhere but explains the next router drops it because its own as is present in the path, not the filter matches unrelated longer as-path sequences and rejects legitimate traffic. This incident is better attributed to the regex was not anchored to the intended as path boundaries.

D:

That explanation fits another condition: Policy unexpectedly modifies MED for every customer route. The evidence here is The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. Its closer root cause is The regex was not anchored to the intended AS path boundaries.

Question 260

A BGP import filter includes a regular expression for customer AS paths. Observed: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. What operational check best guards against this problem returning?

  1. For each approved related change, verify that iPv6 NLRI appears with reachable IPv6 next hops while IPv4 remains stable. Flag recurrence if the IPv4 BGP session is Established but IPv6 route exchange never starts.
  2. For each approved related change, verify that only the intended AS-path patterns trigger the route filter. Flag recurrence if the filter matches unrelated longer AS-path sequences and rejects legitimate traffic.
  3. For each approved related change, verify that an authorized loop-free path is accepted and no repeated AS numbers cause rejection. Flag recurrence if the next router drops it because its own AS is present in the path.
  4. For each approved related change, verify that mED differs only on targeted routes and unrelated announcements remain unchanged. Flag recurrence if policy unexpectedly modifies MED for every customer route.

Explanation

Correct Answer

B:

This control asks for the same recovery evidence (Only the intended AS-path patterns trigger the route filter) and flags recurrence of the same failure (The filter matches unrelated longer AS-path sequences and rejects legitimate traffic). It targets the underlying issue, the regex was not anchored to the intended as path boundaries, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

This gate monitors a different failure, the ipv4 bgp session is established but ipv6 route exchange never starts. It would not detect the current problem: The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. The appropriate check requires only the intended AS-path patterns trigger the route filter.

C:

The proposed control is tied to as-loop prevention correctly rejects a path containing the local autonomous system, typically observed when the next router drops it because its own AS is present in the path. Here the target is the regex was not anchored to the intended as path boundaries; monitor only the intended AS-path patterns trigger the route filter.

D:

It is valid for another service scenario but checks policy unexpectedly modifies med for every customer route. This case instead needs a gate for the filter matches unrelated longer as-path sequences and rejects legitimate traffic and evidence that only the intended AS-path patterns trigger the route filter.

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