Cisco 350-501 Practice Test 37
Question 360
For an original SPCOR service-provider engineering scenario, consider: An IP ping reaches a PE loopback but an L3VPN destination fails because a label binding in the transit LFIB points to the wrong next hop. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Assume loopback ping alone validates every VPN LSP and never inspect the data-plane label stack.
- Change: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Change: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior.
- Check: Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
Explanation
Correct Answer
B:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. Acceptance: The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
E:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. Required intervention: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
Incorrect Answers
A:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D:Change: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Question 361
A service provider network engineer is reviewing this backbone or customer-service scenario: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic. A proposed shortcut is: Assume loopback ping alone validates every VPN LSP and never inspect the data-plane label stack. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
- 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.
- Assume loopback ping alone validates every VPN LSP and never inspect the data-plane label stack.
Explanation
Correct Answer
C:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic.
Incorrect Answers
A:Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
B:Use supported LDP session protection or targeted discovery with routed transport continuity and bounded recovery timers. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. Applied case: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic.
Question 362
A Cisco service provider design review finds: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic. The team proposes: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
- 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.
- SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains.
- MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Explanation
Correct Answer
D:Demonstrable success requires: The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable. Applied case: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic.
Incorrect Answers
A:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
B: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 LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains. A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic.
Question 363
The service provider operations team has not yet approved a change. Current evidence indicates: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic. 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.
- Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
- Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow.
- Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn.
Explanation
Correct Answer
A:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. Confirm afterward that: The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
Incorrect Answers
B:This option addresses a different service provider engineering topic (Unified MPLS core and BGP labeled unicast transport) rather than the documented MPLS OAM LSP ping and traceroute diagnostics decision.
C:Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D:Test link removal, targeted hello maintenance, TCP session state and alternate loopback reachability while measuring session churn. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Question 364
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic. 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.
- The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
- A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed.
- Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
- Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
Explanation
Correct Answer
A:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. The approved implementation step was: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
Incorrect Answers
B:A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid. A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic.
D:Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Question 365
An implementation sign-off request identifies the following problem: A carrier verifies only IGP neighbors after an MPLS outage and never tests the actual forwarding equivalence class that carries VPN traffic. 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: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. Verify: Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
- Change: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure. Verify: Compare computed repair SIDs, protected resource, postfailure path and packet-loss duration under a lab failure.
- 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.
Explanation
Correct Answer
B:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. The change is successful only when: The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
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. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:This option addresses a different service provider engineering topic (TI-LFA topology-independent loop-free repair) rather than the documented MPLS OAM LSP ping and traceroute diagnostics decision.
D:Change: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
Question 366
A service provider network engineer is reviewing this backbone or customer-service scenario: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability. A proposed shortcut is: Assume a plain unlabeled IPv4 route to the distant PE automatically satisfies every cross-domain MPLS VPN label requirement. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Assume a plain unlabeled IPv4 route to the distant PE automatically satisfies every cross-domain MPLS VPN label requirement.
- Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior.
- Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
- Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
Explanation
Correct Answer
D:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability.
Incorrect Answers
A:Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
B:Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
C:Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
Question 367
A Cisco service provider design review finds: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability. The team proposes: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- MPLS TE fast reroute preestablishes backup forwarding or signaling so a point of local repair can redirect LSP traffic quickly after a protected failure.
- MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
- Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
- 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:Demonstrable success requires: Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs. This principle explains the proposed technical approach, which is: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
Incorrect Answers
A:MPLS TE fast reroute preestablishes backup forwarding or signaling so a point of local repair can redirect LSP traffic quickly after a protected failure. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
B:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
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. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
Question 368
The service provider operations team has not yet approved a change. Current evidence indicates: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability. 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 protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
- Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
Explanation
Correct Answer
D:Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed. Applied case: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability.
Incorrect Answers
A:Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
B:Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
C:Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
Question 369
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability. 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.
- Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
- The steered flow crosses the required link and falls back safely if that adjacency is not available.
- Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
- Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
Explanation
Correct Answer
D:Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed. The approved implementation step was: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
Incorrect Answers
A:Traffic does not migrate onto the recovered path until a valid label-switched transport is available. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
B:The steered flow crosses the required link and falls back safely if that adjacency is not available. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
C:Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
Question 370
For an original SPCOR service-provider engineering scenario, consider: A multi-area service provider wants end-to-end labeled transport but only local LDP adjacencies exist and distant PE loopbacks lack consistent label reachability. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
- Change: Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling.
- Check: Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- Change: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
- Assume a plain unlabeled IPv4 route to the distant PE automatically satisfies every cross-domain MPLS VPN label requirement.
Explanation
Correct Answer
A:Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed. Required intervention: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate.
D:Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed. Acceptance: Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
Incorrect Answers
B:This option addresses a different service provider engineering topic (PCE-PCC delegation and SRTE path computation) rather than the documented Unified MPLS core and BGP labeled unicast transport decision.
C:Check: Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
E:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
