Cisco 350-501 Practice Test 36
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.
Question 351
A service provider network engineer is reviewing this backbone or customer-service scenario: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics. 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.
- Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- 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
D:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics.
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. Applied case: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics.
C:Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 352
A Cisco service provider design review finds: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics. 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.
- MPLS TE fast reroute preestablishes backup forwarding or signaling so a point of local repair can redirect LSP traffic quickly after a protected failure.
- TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
- Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
- RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation.
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. Applied case: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics.
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. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
B:TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
D:RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 353
The service provider operations team has not yet approved a change. Current evidence indicates: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Compare computed repair SIDs, protected resource, postfailure path and packet-loss duration under a lab failure.
- Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
Explanation
Correct Answer
D:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. This check tests the actual routing, transport or service boundary before an operationally risky response.
Incorrect Answers
A: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:Compare computed repair SIDs, protected resource, postfailure path and packet-loss duration under a lab failure. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
C:Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 354
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics. 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.
- Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
- Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
- Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation.
- The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
Explanation
Correct Answer
A:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. The approved implementation step was: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior.
Incorrect Answers
B:Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport. 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 (SRv6 locators uSID and interworking gateway) rather than the documented MPLS forwarding labels PHP explicit-null and TTL decision.
D:The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 355
An implementation sign-off request identifies the following problem: A provider requires egress QoS treatment but the design assumes PHP and explicit-null carry identical label information and QoS semantics. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior. Verify: Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
- Change: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate. Verify: Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
- 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: Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling. Verify: Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state.
Explanation
Correct Answer
A:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. The change is successful only when: Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss.
Incorrect Answers
B:Change: Establish end-to-end transport using documented interarea label distribution and BGP labeled-unicast mechanisms where appropriate. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
C:Change: Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node. 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: Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling. Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Question 356
A service provider network engineer is reviewing this backbone or customer-service scenario: 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. 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.
- Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop.
- Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
- Assume loopback ping alone validates every VPN LSP and never inspect the data-plane label stack.
Explanation
Correct Answer
B:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: 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.
Incorrect Answers
A:Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity. 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. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
Question 357
A Cisco service provider design review finds: 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. 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.
- MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
- A Path Computation Element calculates constraints-based paths while the PCC enforces or requests them, and PCEP sessions and delegation govern their coordination.
- RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation.
- 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:Demonstrable success requires: The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable. Applied case: 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.
Incorrect Answers
B:A Path Computation Element calculates constraints-based paths while the PCC enforces or requests them, and PCEP sessions and delegation govern their coordination. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:RSVP-TE establishes signaled label-switched paths using path and reservation messages, while IGP TE extensions distribute topology constraints for computation. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D: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.
Question 358
The service provider operations team has not yet approved a change. Current evidence indicates: 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. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
- Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
- Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops.
- Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
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. Applied case: 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.
Incorrect Answers
A:This option addresses a different service provider engineering topic (RSVP TE fast reroute and local protection) rather than the documented MPLS OAM LSP ping and traceroute diagnostics decision.
C:Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D:Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Question 359
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: 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. 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 headend accepts only valid controller-computed paths and falls back according to defined policy when PCE control is unavailable.
- The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable.
- Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not.
- Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
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 result must be validated using the documented device, service or access context.
Incorrect Answers
A:The headend accepts only valid controller-computed paths and falls back according to defined policy when PCE control is unavailable. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
C:Protected sessions survive the intended transient path change when peer transport remains viable and expire safely if it does not. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
D:Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid. MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
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.
