Cisco 350-501 Practice Test 34
Question 330
For an original SPCOR service-provider engineering scenario, consider: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Force the IGP interface to its lowest cost immediately at link-up regardless of LDP neighbor state.
- Change: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
- Check: Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state.
- Change: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
- Check: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
Explanation
Correct Answer
D:Acceptance: Traffic does not migrate onto the recovered path until a valid label-switched transport is available. Applied case: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch.
E:Acceptance: Traffic does not migrate onto the recovered path until a valid label-switched transport is available. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Incorrect Answers
A:MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration. Use this instead: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
B:Change: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C:Check: Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Question 331
A service provider network engineer is reviewing this backbone or customer-service scenario: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable. A proposed shortcut is: Force the IGP interface to its lowest cost immediately at link-up regardless of LDP neighbor state. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
- Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
- Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes.
- Force the IGP interface to its lowest cost immediately at link-up regardless of LDP neighbor state.
Explanation
Correct Answer
B:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable.
Incorrect Answers
A:Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C:Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
D:MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration. Applied case: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable.
Question 332
A Cisco service provider design review finds: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable. The team proposes: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path. 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.
- SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains.
- 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.
- MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Explanation
Correct Answer
D:Demonstrable success requires: Traffic does not migrate onto the recovered path until a valid label-switched transport is available. Applied case: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable.
Incorrect Answers
A:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C: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. A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable.
Question 333
The service provider operations team has not yet approved a change. Current evidence indicates: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
- Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
- Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
Explanation
Correct Answer
D:Confirm afterward that: Traffic does not migrate onto the recovered path until a valid label-switched transport is available. Applied case: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable.
Incorrect Answers
A:Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C:Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Question 334
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable. 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.
- Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
- The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
- Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
- Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
Explanation
Correct Answer
D:MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C:Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Question 335
An implementation sign-off request identifies the following problem: A maintenance shutdown causes the IGP to prefer a fresh LDP-disabled segment while label forwarding is still unavailable. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. Verify: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Change: Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node. Verify: Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
- Change: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path. Verify: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- 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.
Explanation
Correct Answer
C:The change is successful only when: Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
Incorrect Answers
A:Change: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
B:This option addresses a different service provider engineering topic (RSVP TE fast reroute and local protection) rather than the documented LDP IGP synchronization and blackhole avoidance decision.
D:Change: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
Question 336
A service provider network engineer is reviewing this backbone or customer-service scenario: 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. 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.
- Set unlimited session retention after any physical failure and ignore whether the peer transport address is still reachable.
- Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers.
- Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
Explanation
Correct Answer
B:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Incorrect Answers
A:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
C: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:Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 337
A Cisco service provider design review finds: 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. 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.
- 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.
- MPLS TE fast reroute preestablishes backup forwarding or signaling so a point of local repair can redirect LSP traffic quickly after a protected failure.
- 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.
- LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Explanation
Correct Answer
D:Relevant validation before approval: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn. Demonstrable success requires: Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
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. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
B:MPLS TE fast reroute preestablishes backup forwarding or signaling so a point of local repair can redirect LSP traffic quickly after a protected failure. This option addresses a different service provider engineering topic (RSVP TE fast reroute and local protection) rather than the documented LDP session protection and targeted transport decision. The case-specific mechanism is: LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. The relevant action is: Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers. Discriminating evidence: Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn. Applied case: 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.
C: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. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 338
The service provider operations team has not yet approved a change. Current evidence indicates: 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. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
- Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
- 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. Confirm afterward that: Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
Incorrect Answers
A:This option addresses a different service provider engineering topic (MPLS LDP neighbor discovery and label switching) rather than the documented LDP session protection and targeted transport decision.
B: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.
C:Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
Question 339
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: 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. 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.
- Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation.
- Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
- Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
- A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed.
Explanation
Correct Answer
C:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
B:Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
D:A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed. LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
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.
