Cisco 350-501 Practice Test 43
Question 420
For an original SPCOR service-provider engineering scenario, consider: A provider defines two SRTE candidate paths but the headend fails to steer selected services into the intended color and endpoint policy. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
- Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
- Configure an unused SR policy and assume all customer packets automatically steer onto it without classification or binding.
- Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Change: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
Explanation
Correct Answer
A: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. Required intervention: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
E: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. Evidence: Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
Incorrect Answers
B:Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. 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.
C:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. 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.
D:Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. 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.
Question 421
A service provider network engineer is reviewing this backbone or customer-service scenario: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked. A proposed shortcut is: Configure an unused SR policy and assume all customer packets automatically steer onto it without classification or binding. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
- Configure an unused SR policy and assume all customer packets automatically steer onto it without classification or binding.
- Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
- 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 controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked.
Incorrect Answers
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. Applied case: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked.
C:Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. 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.
D:Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node. 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.
Question 422
A Cisco service provider design review finds: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked. The team proposes: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- 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.
- 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.
- A Path Computation Element calculates constraints-based paths while the PCC enforces or requests them, and PCEP sessions and delegation govern their coordination.
Explanation
Correct Answer
C:Demonstrable success requires: Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid. Applied case: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked.
Incorrect Answers
A:SRv6 encodes endpoint functions in IPv6 SIDs and uSID compresses supported behavior sequences; interworking gateways translate service or transport context between domains. 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.
B:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. 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.
D:This option addresses a different service provider engineering topic (PCE-PCC delegation and SRTE path computation) rather than the documented SR policy candidate paths and SRTE endpoint steering decision.
Question 423
The service provider operations team has not yet approved a change. Current evidence indicates: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
- Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
Explanation
Correct Answer
C: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. This check tests the actual routing, transport or service boundary before an operationally risky response.
Incorrect Answers
A:Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops. 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.
B:Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router. 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.
D:Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled. 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.
Question 424
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked. 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.
- Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
- Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
- 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: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. The approved implementation step was: Bind the service steering rule to the correct SR policy color and endpoint and validate candidate preference, segment-list resolution and policy validity.
Incorrect Answers
B:Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs. A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked.
C:Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation. 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.
D:The faulty label operation or transit hop is identified and repaired while core IP adjacencies stay stable. 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.
Question 425
An implementation sign-off request identifies the following problem: A controller supplies a path that crosses a maintenance link while traffic still uses an older lower-preference SR policy because candidate selection was not checked. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- 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.
- 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: Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes. Verify: Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow.
- 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
A: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. The change is successful only when: Targeted traffic follows the active approved policy and reacts predictably when the selected candidate becomes invalid.
Incorrect Answers
B:Change: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. 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.
C:Change: Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes. 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.
D:Change: Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path. 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.
Question 426
A service provider network engineer is reviewing this backbone or customer-service scenario: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path. A proposed shortcut is: Use any alternate interface as TI-LFA protection without checking the backup path for loops or failed-resource traversal. 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.
- Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
- Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
- Use any alternate interface as TI-LFA protection without checking the backup path for loops or failed-resource traversal.
Explanation
Correct Answer
B:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. The required acceptance condition is: Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route.
Incorrect Answers
A:Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
C:Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
D:TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
Question 427
A Cisco service provider design review finds: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path. The team proposes: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure. 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.
- TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
- MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
- Unified MPLS extends labeled reachability across IGP boundaries while keeping each IGP domain scalable, but label continuity and next-hop resolution must be designed.
Explanation
Correct Answer
B:Demonstrable success requires: Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route. This principle explains the proposed technical approach, which is: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
Incorrect Answers
A:This option addresses a different service provider engineering topic (MPLS OAM LSP ping and traceroute diagnostics) rather than the documented TI-LFA topology-independent loop-free repair decision.
C:MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
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. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
Question 428
The service provider operations team has not yet approved a change. Current evidence indicates: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
- 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.
- Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow.
Explanation
Correct Answer
C:Confirm afterward that: Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route. Applied case: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path.
Incorrect Answers
A:Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
B:Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
D:This option addresses a different service provider engineering topic (SRv6 locators uSID and interworking gateway) rather than the documented TI-LFA topology-independent loop-free repair decision.
Question 429
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair 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.
- Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
- Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
- Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route.
- The intended traffic resumes over an eligible repair path within the service convergence target and no protection loop is created.
Explanation
Correct Answer
C:TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Traffic does not migrate onto the recovered path until a valid label-switched transport is available. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
B:Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
D:The intended traffic resumes over an eligible repair path within the service convergence target and no protection loop is created. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
Question 430
For an original SPCOR service-provider engineering scenario, consider: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Change: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
- Change: Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node.
- Check: Compare computed repair SIDs, protected resource, postfailure path and packet-loss duration under a lab failure.
- Use any alternate interface as TI-LFA protection without checking the backup path for loops or failed-resource traversal.
- Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
Explanation
Correct Answer
A:Acceptance: Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route. Applied case: An SR-MPLS router loses its primary next hop and waits for full IGP convergence though its topology has a viable postconvergence repair path.
C:Acceptance: Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
Incorrect Answers
B:Change: Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
D:TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure. Use this instead: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
E:Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test. TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
