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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 32

Question 310

A BGP router has imported a route with an unexpected AS path. Observed: The next router drops it because its own AS is present in the path. What evidence would validate recovery from this precise failure mode?

  1. MED differs only on targeted routes and unrelated announcements remain unchanged.
  2. Remote customer sees its contracted prefixes without provider loopbacks.
  3. The receiver sees the complete three-part community and classifies it correctly.
  4. An authorized loop-free path is accepted and no repeated AS numbers cause rejection.

Explanation

Correct Answer

D:

The intended result is An authorized loop-free path is accepted and no repeated AS numbers cause rejection. It specifically verifies recovery from as-loop prevention correctly rejects a path containing the local autonomous system, which produced the original symptom: The next router drops it because its own AS is present in the path. It is stronger evidence than a generic interface-up indicator.

Incorrect Answers

A:

This result is useful in another case with evidence Policy unexpectedly modifies MED for every customer route. It does not test recovery from the next router drops it because its own as is present in the path. Check instead whether an authorized loop-free path is accepted and no repeated AS numbers cause rejection.

B:

That observation would verify a separate fault involving bgp export policy is too broad for the neighbor's contractual prefix set. Its symptom is The transit edge begins advertising an infrastructure loopback to an external customer. For this case the actual issue is as-loop prevention correctly rejects a path containing the local autonomous system, and the relevant success signal is An authorized loop-free path is accepted and no repeated AS numbers cause rejection.

C:

It confirms an unrelated service correction: Standard communities do not provide the three-field large-community semantics. The present case reports The next router drops it because its own AS is present in the path. Its completion test is An authorized loop-free path is accepted and no repeated AS numbers cause rejection.

Question 311

A BGP router has imported a route with an unexpected AS path. Observed: The next router drops it because its own AS is present in the path. What underlying protocol or service configuration problem best explains the evidence?

  1. A broad routing-policy term matches routes outside its intended customer prefix list.
  2. BGP export policy is too broad for the neighbor's contractual prefix set.
  3. Standard communities do not provide the three-field large-community semantics.
  4. AS-loop prevention correctly rejects a path containing the local autonomous system.

Explanation

Correct Answer

D:

Because the next router drops it because its own AS is present in the path, the likely cause is as-loop prevention correctly rejects a path containing the local autonomous system. It is testable: Remove the accidental AS-path loop or redesign the session without broad allow-as loops. Expected follow-up: An authorized loop-free path is accepted and no repeated AS numbers cause rejection.

Incorrect Answers

A:

That explanation fits another condition: Policy unexpectedly modifies MED for every customer route. The evidence here is The next router drops it because its own AS is present in the path. Its closer root cause is AS-loop prevention correctly rejects a path containing the local autonomous system.

B:

The stated cause is possible elsewhere but explains the transit edge begins advertising an infrastructure loopback to an external customer, not the next router drops it because its own as is present in the path. This incident is better attributed to as-loop prevention correctly rejects a path containing the local autonomous system.

C:

Standard communities do not provide the three-field large-community semantics. would normally be accompanied by a 32-bit community representation cannot encode the required triple of values. The observed symptom is different: The next router drops it because its own AS is present in the path. The likely cause is AS-loop prevention correctly rejects a path containing the local autonomous system.

Question 312

A BGP router has imported a route with an unexpected AS path. Observed: The next router drops it because its own AS is present in the path. Which ongoing validation gate would best detect a recurrence of this problem?

  1. 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.
  2. For each approved related change, verify that remote customer sees its contracted prefixes without provider loopbacks. Flag recurrence if the transit edge begins advertising an infrastructure loopback to an external customer.
  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 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.

Explanation

Correct Answer

D:

A useful regression gate tests whether an authorized loop-free path is accepted and no repeated AS numbers cause rejection and alerts when the next router drops it because its own AS is present in the path. This directly checks the technical weakness: AS-loop prevention correctly rejects a path containing the local autonomous system. The gate is derived from the fictional incident and is not an independent Juniper engineer signoff.

Incorrect Answers

A:

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 next router drops it because its own as is present in the path and evidence that an authorized loop-free path is accepted and no repeated AS numbers cause rejection.

B:

The proposed control is tied to bgp export policy is too broad for the neighbor's contractual prefix set, typically observed when the transit edge begins advertising an infrastructure loopback to an external customer. Here the target is as-loop prevention correctly rejects a path containing the local autonomous system; monitor an authorized loop-free path is accepted and no repeated AS numbers cause rejection.

C:

This gate monitors a different failure, a 32-bit community representation cannot encode the required triple of values. It would not detect the current problem: The next router drops it because its own AS is present in the path. The appropriate check requires an authorized loop-free path is accepted and no repeated AS numbers cause rejection.

Question 313

A provider wants to keep internal network prefixes private. Observed: The transit edge begins advertising an infrastructure loopback to an external customer. Which change most directly corrects the failure while respecting the existing service boundary?

  1. Require authenticated allowed-prefix and specificity checks before community-triggered discard.
  2. Explicitly permit only authorized customer announcements and reject internal infrastructure routes.
  3. Rewrite and test the policy expression against permitted and blocked AS paths.
  4. Reinstate the agreed route family and prefix export policy with validation.

Explanation

Correct Answer

B:

The observed condition is The transit edge begins advertising an infrastructure loopback to an external customer. That indicates bgp export policy is too broad for the neighbor's contractual prefix set. Applying the proposed remedy directly changes that condition. A concrete completion check is: Remote customer sees its contracted prefixes without provider loopbacks.

Incorrect Answers

A:

This change belongs to a different BGP issue: The provider edge accepts a blackhole community with a customer-controlled unbounded prefix. That issue involves the policy does not verify source authorization or maximum route specificity. The current symptom is The transit edge begins advertising an infrastructure loopback to an external customer. It instead requires explicitly permit only authorized customer announcements and reject internal infrastructure routes.

C:

The option may be useful when the filter matches unrelated longer AS-path sequences and rejects legitimate traffic, but that is not the current evidence. Here, the transit edge begins advertising an infrastructure loopback to an external customer, indicating bgp export policy is too broad for the neighbor's contractual prefix set. The targeted action is Explicitly permit only authorized customer announcements and reject internal infrastructure routes.

D:

This remediates a peer export policy was accidentally changed to advertise default only, normally indicated by Specific destination prefixes disappear from the customer route table. It would leave the observed problem (The transit edge begins advertising an infrastructure loopback to an external customer) unresolved. Address it with explicitly permit only authorized customer announcements and reject internal infrastructure routes.

Question 314

A provider wants to keep internal network prefixes private. Observed: The transit edge begins advertising an infrastructure loopback to an external customer. 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. Only allowed attack destinations are suppressed and legitimate prefixes remain forwarding.
  3. The customer receives exactly the contracted specific prefixes and default behavior.
  4. Remote customer sees its contracted prefixes without provider loopbacks.

Explanation

Correct Answer

D:

After explicitly permit only authorized customer announcements and reject internal infrastructure routes, inspect whether remote customer sees its contracted prefixes without provider loopbacks. This closes the loop between the reported observation (The transit edge begins advertising an infrastructure loopback to an external customer) and the underlying issue (BGP export policy is too broad for the neighbor's contractual prefix set).

Incorrect Answers

A:

That observation would verify a separate fault involving the regex was not anchored to the intended as path boundaries. Its symptom is The filter matches unrelated longer AS-path sequences and rejects legitimate traffic. For this case the actual issue is bgp export policy is too broad for the neighbor's contractual prefix set, and the relevant success signal is Remote customer sees its contracted prefixes without provider loopbacks.

B:

It confirms an unrelated service correction: The policy does not verify source authorization or maximum route specificity. The present case reports The transit edge begins advertising an infrastructure loopback to an external customer. Its completion test is Remote customer sees its contracted prefixes without provider loopbacks.

C:

This result is useful in another case with evidence Specific destination prefixes disappear from the customer route table. It does not test recovery from the transit edge begins advertising an infrastructure loopback to an external customer. Check instead whether remote customer sees its contracted prefixes without provider loopbacks.

Question 315

A provider wants to keep internal network prefixes private. Observed: The transit edge begins advertising an infrastructure loopback to an external customer. Which root cause is most consistent with this symptom?

  1. A peer export policy was accidentally changed to advertise default only.
  2. The regex was not anchored to the intended AS path boundaries.
  3. The policy does not verify source authorization or maximum route specificity.
  4. BGP export policy is too broad for the neighbor's contractual prefix set.

Explanation

Correct Answer

D:

The reported evidence—The transit edge begins advertising an infrastructure loopback to an external customer—supports bgp export policy is too broad for the neighbor's contractual prefix set. The appropriate intervention is to explicitly permit only authorized customer announcements and reject internal infrastructure routes, with confirmation from remote customer sees its contracted prefixes without provider loopbacks. Other causes require actual device-state verification.

Incorrect Answers

A:

That explanation fits another condition: Specific destination prefixes disappear from the customer route table. The evidence here is The transit edge begins advertising an infrastructure loopback to an external customer. Its closer root cause is BGP export policy is too broad for the neighbor's contractual prefix set.

B:

The stated cause is possible elsewhere but explains the filter matches unrelated longer as-path sequences and rejects legitimate traffic, not the transit edge begins advertising an infrastructure loopback to an external customer. This incident is better attributed to bgp export policy is too broad for the neighbor's contractual prefix set.

C:

The policy does not verify source authorization or maximum route specificity. would normally be accompanied by the provider edge accepts a blackhole community with a customer-controlled unbounded prefix. The observed symptom is different: The transit edge begins advertising an infrastructure loopback to an external customer. The likely cause is BGP export policy is too broad for the neighbor's contractual prefix set.

Question 316

A provider wants to keep internal network prefixes private. Observed: The transit edge begins advertising an infrastructure loopback to an external customer. Which change-acceptance control is most relevant to preventing this exact failure?

  1. For each approved related change, verify that remote customer sees its contracted prefixes without provider loopbacks. Flag recurrence if the transit edge begins advertising an infrastructure loopback to an external customer.
  2. For each approved related change, verify that the customer receives exactly the contracted specific prefixes and default behavior. Flag recurrence if specific destination prefixes disappear from the customer route table.
  3. For each approved related change, verify that only allowed attack destinations are suppressed and legitimate prefixes remain forwarding. Flag recurrence if the provider edge accepts a blackhole community with a customer-controlled unbounded prefix.
  4. 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.

Explanation

Correct Answer

A:

The control is specific to the initial failure. It requires the result Remote customer sees its contracted prefixes without provider loopbacks. and treats The transit edge begins advertising an infrastructure loopback to an external customer. as a failure signal. The causal concern is bgp export policy is too broad for the neighbor's contractual prefix set.

Incorrect Answers

B:

It is valid for another service scenario but checks specific destination prefixes disappear from the customer route table. This case instead needs a gate for the transit edge begins advertising an infrastructure loopback to an external customer and evidence that remote customer sees its contracted prefixes without provider loopbacks.

C:

This gate monitors a different failure, the provider edge accepts a blackhole community with a customer-controlled unbounded prefix. It would not detect the current problem: The transit edge begins advertising an infrastructure loopback to an external customer. The appropriate check requires remote customer sees its contracted prefixes without provider loopbacks.

D:

The proposed control is tied to the regex was not anchored to the intended as path boundaries, typically observed when the filter matches unrelated longer AS-path sequences and rejects legitimate traffic. Here the target is bgp export policy is too broad for the neighbor's contractual prefix set; monitor remote customer sees its contracted prefixes without provider loopbacks.

Question 317

A BGP customer edge receives an unexpected default-only route after peering work. Observed: Specific destination prefixes disappear from the customer route table. What should the routing engineer change first to address this particular symptom?

  1. Reinstate the agreed route family and prefix export policy with validation.
  2. Align neighbor addresses and peer AS configuration with the authorized session design.
  3. Lower backup desirability via a consistent local policy and test withdrawal.
  4. Enable the intended multiprotocol IPv6 unicast family on both neighbors.

Explanation

Correct Answer

A:

The decisive evidence is that Specific destination prefixes disappear from the customer route table. This follows from a peer export policy was accidentally changed to advertise default only. The focused remedy is to reinstate the agreed route family and prefix export policy with validation. Confirm improvement when the customer receives exactly the contracted specific prefixes and default behavior. Validate on an approved lab or change window before touching production.

Incorrect Answers

B:

The option may be useful when bGP remains Idle even though next-hop IPs respond to ping, but that is not the current evidence. Here, specific destination prefixes disappear from the customer route table, indicating a peer export policy was accidentally changed to advertise default only. The targeted action is Reinstate the agreed route family and prefix export policy with validation.

C:

This change belongs to a different BGP issue: Backup path is preferred when an origin prefix first appears. That issue involves import policy assigns the backup a higher preference or local preference. The current symptom is Specific destination prefixes disappear from the customer route table. It instead requires reinstate the agreed route family and prefix export policy with validation.

D:

This remediates ipv6 address-family activation is missing for that neighbor, normally indicated by The IPv4 BGP session is Established but IPv6 route exchange never starts. It would leave the observed problem (Specific destination prefixes disappear from the customer route table) unresolved. Address it with reinstate the agreed route family and prefix export policy with validation.

Question 318

A BGP customer edge receives an unexpected default-only route after peering work. Observed: Specific destination prefixes disappear from the customer route table. Which acceptance observation best confirms that the proposed change worked?

  1. IPv6 NLRI appears with reachable IPv6 next hops while IPv4 remains stable.
  2. The customer receives exactly the contracted specific prefixes and default behavior.
  3. Primary path wins normally and backup activates on controlled failure.
  4. The intended external BGP session establishes and the agreed routes appear.

Explanation

Correct Answer

B:

This acceptance criterion tests the actual fault. The source evidence was Specific destination prefixes disappear from the customer route table. The correction addresses a peer export policy was accidentally changed to advertise default only; success requires the customer receives exactly the contracted specific prefixes and default behavior.

Incorrect Answers

A:

This result is useful in another case with evidence The IPv4 BGP session is Established but IPv6 route exchange never starts. It does not test recovery from specific destination prefixes disappear from the customer route table. Check instead whether the customer receives exactly the contracted specific prefixes and default behavior.

C:

It confirms an unrelated service correction: Import policy assigns the backup a higher preference or local preference. The present case reports Specific destination prefixes disappear from the customer route table. Its completion test is The customer receives exactly the contracted specific prefixes and default behavior.

D:

That observation would verify a separate fault involving the remote neighbor ip or expected autonomous-system setting does not match the peering contract. Its symptom is BGP remains Idle even though next-hop IPs respond to ping. For this case the actual issue is a peer export policy was accidentally changed to advertise default only, and the relevant success signal is The customer receives exactly the contracted specific prefixes and default behavior.

Question 319

A BGP customer edge receives an unexpected default-only route after peering work. Observed: Specific destination prefixes disappear from the customer route table. What is the most likely source of the observed routing or service failure?

  1. IPv6 address-family activation is missing for that neighbor.
  2. Import policy assigns the backup a higher preference or local preference.
  3. A peer export policy was accidentally changed to advertise default only.
  4. The remote neighbor IP or expected autonomous-system setting does not match the peering contract.

Explanation

Correct Answer

C:

This explanation is the closest match to the observed symptom: Specific destination prefixes disappear from the customer route table. The specified root issue is A peer export policy was accidentally changed to advertise default only. Repair it through reinstate the agreed route family and prefix export policy with validation, then check the customer receives exactly the contracted specific prefixes and default behavior.

Incorrect Answers

A:

That explanation fits another condition: The IPv4 BGP session is Established but IPv6 route exchange never starts. The evidence here is Specific destination prefixes disappear from the customer route table. Its closer root cause is A peer export policy was accidentally changed to advertise default only.

B:

Import policy assigns the backup a higher preference or local preference. would normally be accompanied by backup path is preferred when an origin prefix first appears. The observed symptom is different: Specific destination prefixes disappear from the customer route table. The likely cause is A peer export policy was accidentally changed to advertise default only.

D:

The stated cause is possible elsewhere but explains bgp remains idle even though next-hop ips respond to ping, not specific destination prefixes disappear from the customer route table. This incident is better attributed to a peer export policy was accidentally changed to advertise default only.

Question 320

A BGP customer edge receives an unexpected default-only route after peering work. Observed: Specific destination prefixes disappear from the customer route table. What operational check best guards against this problem returning?

  1. For each approved related change, verify that the intended external BGP session establishes and the agreed routes appear. Flag recurrence if bGP remains Idle even though next-hop IPs respond to ping.
  2. 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.
  3. For each approved related change, verify that primary path wins normally and backup activates on controlled failure. Flag recurrence if backup path is preferred when an origin prefix first appears.
  4. For each approved related change, verify that the customer receives exactly the contracted specific prefixes and default behavior. Flag recurrence if specific destination prefixes disappear from the customer route table.

Explanation

Correct Answer

D:

This control asks for the same recovery evidence (The customer receives exactly the contracted specific prefixes and default behavior) and flags recurrence of the same failure (Specific destination prefixes disappear from the customer route table). It targets the underlying issue, a peer export policy was accidentally changed to advertise default only, rather than a different service problem. The exact cadence must be agreed with operations.

Incorrect Answers

A:

The proposed control is tied to the remote neighbor ip or expected autonomous-system setting does not match the peering contract, typically observed when bGP remains Idle even though next-hop IPs respond to ping. Here the target is a peer export policy was accidentally changed to advertise default only; monitor the customer receives exactly the contracted specific prefixes and default behavior.

B:

It is valid for another service scenario but checks the ipv4 bgp session is established but ipv6 route exchange never starts. This case instead needs a gate for specific destination prefixes disappear from the customer route table and evidence that the customer receives exactly the contracted specific prefixes and default behavior.

C:

This gate monitors a different failure, backup path is preferred when an origin prefix first appears. It would not detect the current problem: Specific destination prefixes disappear from the customer route table. The appropriate check requires the customer receives exactly the contracted specific prefixes and default behavior.

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