Cisco 350-501 Practice Test 35
Question 340
For an original SPCOR service-provider engineering scenario, consider: A core router experiences a brief direct link loss and repeatedly tears down its remote LDP session although an alternate routed path to the peer exists. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Change: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
- Change: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Check: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
- Check: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
- Set unlimited session retention after any physical failure and ignore whether the peer transport address is still reachable.
Explanation
Correct Answer
A:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. Evidence: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
C:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. Acceptance: Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
Incorrect Answers
B:Change: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
D:Check: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
E:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 341
A service provider network engineer is reviewing this backbone or customer-service scenario: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path. A proposed shortcut is: Set unlimited session retention after any physical failure and ignore whether the peer transport address is still reachable. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
- Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
- Set unlimited session retention after any physical failure and ignore whether the peer transport address is still reachable.
- Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node.
Explanation
Correct Answer
A:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path.
Incorrect Answers
B:Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
C:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. Applied case: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path.
D:Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 342
A Cisco service provider design review finds: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path. The team proposes: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
- RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation.
- A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values.
- SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains.
Explanation
Correct Answer
A:Relevant validation before approval: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn. Applied case: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path.
Incorrect Answers
B:RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
C:A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values. A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path.
D:SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 343
The service provider operations team has not yet approved a change. Current evidence indicates: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
Explanation
Correct Answer
D:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. This check tests the actual routing, transport or service boundary before an operationally risky response.
Incorrect Answers
A:Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
B:Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
C:This option addresses a different service provider engineering topic (LDP IGP synchronization and blackhole avoidance) rather than the documented LDP session protection and targeted transport decision.
Question 344
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path. The carrier operations owner needs positive and negative tests showing existing customer services remain available. Which acceptance result demonstrates correct service provider forwarding and control behavior without disrupting authorized workflows? Select ONE best answer.
- Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
- Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
- The steered flow crosses the required link and falls back safely if that adjacency is not available.
- Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
Explanation
Correct Answer
A:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. The approved implementation step was: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
Incorrect Answers
B:Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
C:The steered flow crosses the required link and falls back safely if that adjacency is not available. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
D:Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 345
An implementation sign-off request identifies the following problem: A provider expects a targeted LDP discovery session to survive an access link event but its transport address becomes unreachable over the backup IGP path. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers. Verify: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
- Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. Verify: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
- Change: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. Verify: Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops.
- Change: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity. Verify: Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
Explanation
Correct Answer
A:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. The change is successful only when: Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
Incorrect Answers
B:Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
C:Change: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
D:Change: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
Question 346
A service provider network engineer is reviewing this backbone or customer-service scenario: An engineer mistakes a penultimate-hop pop for a lost label and disables MPLS after seeing unlabeled delivery at the egress PE. A proposed shortcut is: Treat every popped transport label as proof of an invalid MPLS path and reinsert arbitrary labels without checking LFIB state. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
- Treat every popped transport label as proof of an invalid MPLS path and reinsert arbitrary labels without checking LFIB state.
- Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior.
- Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
Explanation
Correct Answer
C:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Incorrect Answers
A:Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
B:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
D:Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 347
A Cisco service provider design review finds: An engineer mistakes a penultimate-hop pop for a lost label and disables MPLS after seeing unlabeled delivery at the egress PE. The team proposes: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values.
- SR traffic engineering policies select candidate paths and instantiate explicit forwarding segments; configuration alone does not prove a policy is active or matched by traffic.
- Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
- A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence.
Explanation
Correct Answer
C:Relevant validation before approval: Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null. Demonstrable success requires: Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
Incorrect Answers
A:A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
B:SR traffic engineering policies select candidate paths and instantiate explicit forwarding segments; configuration alone does not prove a policy is active or matched by traffic. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
D:A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 348
The service provider operations team has not yet approved a change. Current evidence indicates: An engineer mistakes a penultimate-hop pop for a lost label and disables MPLS after seeing unlabeled delivery at the egress PE. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
- Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
- Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state.
Explanation
Correct Answer
B:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. Confirm afterward that: Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
Incorrect Answers
A:Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
C:This option addresses a different service provider engineering topic (MPLS LDP neighbor discovery and label switching) rather than the documented MPLS forwarding labels PHP explicit-null and TTL decision.
D:Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 349
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: An engineer mistakes a penultimate-hop pop for a lost label and disables MPLS after seeing unlabeled delivery at the egress PE. The carrier operations owner needs positive and negative tests showing existing customer services remain available. Which acceptance result demonstrates correct service provider forwarding and control behavior without disrupting authorized workflows? Select ONE best answer.
- A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed.
- Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
- Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
- The intended traffic resumes over an eligible repair path within the service convergence target and no protection loop is created.
Explanation
Correct Answer
B:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
C:Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
D:The intended traffic resumes over an eligible repair path within the service convergence target and no protection loop is created. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 350
For an original SPCOR service-provider engineering scenario, consider: An engineer mistakes a penultimate-hop pop for a lost label and disables MPLS after seeing unlabeled delivery at the egress PE. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Treat every popped transport label as proof of an invalid MPLS path and reinsert arbitrary labels without checking LFIB state.
- Check: Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
- Change: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
- Change: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior.
Explanation
Correct Answer
C:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. Acceptance: Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
E:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. Evidence: Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
Incorrect Answers
A:Check: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
B:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
D:Change: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
