Cisco 350-501 Practice Test 33
Question 320
For an original SPCOR service-provider engineering scenario, consider: Two provider core routers have a healthy OSPF adjacency but form no LDP session because a loopback transport address is unreachable. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Change: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints.
- Change: Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop.
- Check: Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- Assume successful OSPF route exchange makes LDP operational even when its TCP session and label bindings are absent.
- Check: Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow.
Explanation
Correct Answer
B:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. Evidence: Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
C:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. Required intervention: Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop.
Incorrect Answers
A:Change: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
D:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
E:Check: Check IPv6 locator advertisements, SID behavior, encapsulation and decapsulation and gateway forwarding for a test VPN or steered flow. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
Question 321
A service provider network engineer is reviewing this backbone or customer-service scenario: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path. A proposed shortcut is: Assume successful OSPF route exchange makes LDP operational even when its TCP session and label bindings are absent. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Assume successful OSPF route exchange makes LDP operational even when its TCP session and label bindings are absent.
- Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints.
- Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop.
Explanation
Correct Answer
D:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path.
Incorrect Answers
A:Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
B:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. Applied case: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path.
C:Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
Question 322
A Cisco service provider design review finds: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path. The team proposes: Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop. 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.
- 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.
- MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
- 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.
Explanation
Correct Answer
A:Demonstrable success requires: LDP neighbors become operational on intended links and the requested FEC follows a valid label-switched path end to end. Applied case: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path.
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. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
C:MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
D: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 signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
Question 323
The service provider operations team has not yet approved a change. Current evidence indicates: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
- Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
Explanation
Correct Answer
D:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. This check tests the actual routing, transport or service boundary before an operationally risky response.
Incorrect Answers
A:Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
B:Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
C:Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
Question 324
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched 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.
- Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation.
- LDP neighbors become operational on intended links and the requested FEC follows a valid label-switched path end to end.
- Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
- The steered flow crosses the required link and falls back safely if that adjacency is not available.
Explanation
Correct Answer
B:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. The approved implementation step was: Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop.
Incorrect Answers
A:Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
C:Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
D:The steered flow crosses the required link and falls back safely if that adjacency is not available. LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
Question 325
An implementation sign-off request identifies the following problem: A PE uses MPLS on only one side of an uplink and an unlabeled packet cannot traverse an intended LDP-based label-switched path. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Verify MPLS forwarding activation, LDP discovery and reachable transport addresses on every required core hop. Verify: Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- 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: 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:LDP signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready. The change is successful only when: LDP neighbors become operational on intended links and the requested FEC follows a valid label-switched path end to end.
Incorrect Answers
B:Change: Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
C:Change: Configure supported RSVP local protection mechanisms and verify that a prepared bypass or detour can protect the intended link or node.
D:Change: Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling.
Question 326
A service provider network engineer is reviewing this backbone or customer-service scenario: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch. 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.
- 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.
- Coordinate IGP path eligibility with LDP readiness using supported LDP-IGP synchronization and verify label availability before restoring the path.
- Force the IGP interface to its lowest cost immediately at link-up regardless of LDP neighbor state.
Explanation
Correct Answer
C:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. 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.
Incorrect Answers
A:Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:Interpret MPLS label operations, bottom-of-stack state and egress handling based on the signaled FEC and selected pop or explicit-null behavior. 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. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
Question 327
A Cisco service provider design review finds: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch. 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 signaling distributes bindings for forwarding equivalence classes, while an IP routing adjacency alone does not prove label transport is ready.
- A Path Computation Element calculates constraints-based paths while the PCC enforces or requests them, and PCEP sessions and delegation govern their coordination.
- 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: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch.
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 core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
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 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. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Question 328
The service provider operations team has not yet approved a change. Current evidence indicates: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
- Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path.
- Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null.
Explanation
Correct Answer
C:Confirm afterward that: 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.
Incorrect Answers
A:Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:Inspect LDP discovery and session state, transport address routing, label binding and hardware forwarding labels along the path. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
D:Inspect incoming and outgoing labels, label stack operation, TTL and traffic class on a lab LSP with and without explicit-null. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
Question 329
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: An IGP restores a low-cost core link before LDP labels synchronize, drawing VPN traffic onto an IP path that cannot label-switch. 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.
- Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route.
- The headend accepts only valid controller-computed paths and falls back according to defined policy when PCE control is unavailable.
- 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. 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.
Incorrect Answers
A:Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
B:Protected traffic continues through a verified loop-free repair path while IGP converges to a stable new route. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
C:The headend accepts only valid controller-computed paths and falls back according to defined policy when PCE control is unavailable. MPLS core VPN traffic may be blackholed when IGP selects a path before its label transport is operational; LDP synchronization delays cost restoration.
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.
