Cisco 350-501 Practice Test 41
Question 400
For an original SPCOR service-provider engineering scenario, consider: Two core routers advertise the same global prefix SID index for different prefixes, creating inconsistent label meaning across the SR domain. Select THREE compatible elements: a proper correction, a targeted diagnostic and an acceptance result.
- Check: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
- Change: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
- Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
- Check: Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled.
- Result: Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
- Result: Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
Explanation
Correct Answer
A:A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values. Required intervention: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
C: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. Evidence: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
E: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. Result: Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
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. 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.
D:Check: Inspect protected interface and facility state, bypass path validity and measured traffic loss when the link or node is disabled. 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.
F:Result: Traffic does not migrate onto the recovered path until a valid label-switched transport is available. 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.
Question 401
A service provider network engineer is reviewing this backbone or customer-service scenario: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB. A proposed shortcut is: Assign arbitrary overlapping prefix SID indexes and treat the numeric label as globally identical across routers with different SRGBs. 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.
- Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability.
- Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling.
- Assign arbitrary overlapping prefix SID indexes and treat the numeric label as globally identical across routers with different SRGBs.
Explanation
Correct Answer
A:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB.
Incorrect Answers
B:Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. 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.
C:Establish an authenticated PCE-PCC control relationship, current topology data and valid policy delegation or candidate update handling. 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.
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. Applied case: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB.
Question 402
A Cisco service provider design review finds: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB. The team proposes: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence.
- A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values.
- LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport.
- Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling.
Explanation
Correct Answer
B:Demonstrable success requires: Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport. Applied case: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB.
Incorrect Answers
A:A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence. A global prefix SID expresses reachability toward a node or prefix through IGP shortest path, while an SRGB maps SID indexes into local label values.
C:LDP session protection can preserve an established LDP session using alternate IP reachability during local link interruptions but depends on continued peer transport. 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.
D:Penultimate-hop popping removes the outer transport label before egress, while explicit-null retains a label where required for policy or QoS handling. 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.
Question 403
The service provider operations team has not yet approved a change. Current evidence indicates: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding.
- Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
- Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
- Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state.
Explanation
Correct Answer
C: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. This check tests the actual routing, transport or service boundary before an operationally risky response.
Incorrect Answers
A:Trace remote PE loopback route and label advertisements through each border node, then validate transport LSP and VPN service forwarding. 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.
B:Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route. 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.
D:Inspect PCEP session state, computed path constraints, delegated policy ownership, SID reachability and actual headend candidate state. 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.
Question 404
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB. 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.
- The headend accepts only valid controller-computed paths and falls back according to defined policy when PCE control is unavailable.
- Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs.
- Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
Explanation
Correct Answer
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. The approved implementation step was: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
Incorrect Answers
A:Transit and egress forwarding agree with the selected label operation and customer traffic exits at the proper PE without service loss. 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.
B:Applied case: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB.
C:Remote PEs have resolvable label-switched transport paths through interarea boundaries without flooding all service routes into core IGPs. 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.
Question 405
An implementation sign-off request identifies the following problem: A PE receives an SR node SID but attempts forwarding without checking that the SID index fits each router's configured SRGB. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- 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: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. Verify: Check TE database attributes, unreserved bandwidth, ERO or path message and reservation errors across the candidate hops.
- 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: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers. Verify: Inspect prefix SID TLVs, SRGB advertisements, derived labels and outgoing next hops on at least three routers.
Explanation
Correct Answer
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. The change is successful only when: Every router resolves the intended prefix SID consistently and traffic reaches the target node via the valid SR transport.
Incorrect Answers
A:Change: Use MPLS-aware OAM and label-stack inspection to verify LSP forwarding and localize transport failures separate from ordinary IP reachability. 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.
B:Change: Advertise accurate TE topology and choose a path whose available reservable bandwidth satisfies the RSVP-TE tunnel constraints. 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.
C:Change: Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes.
Question 406
A service provider network engineer is reviewing this backbone or customer-service scenario: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link. A proposed shortcut is: Use only a destination node SID and promise deterministic traversal of a particular ECMP member without an adjacency segment. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Use only a destination node SID and promise deterministic traversal of a particular ECMP member without an adjacency segment.
- Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure.
- Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes.
- Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
Explanation
Correct Answer
D:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link.
Incorrect Answers
A: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. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
B:Enable a supported TI-LFA protection mechanism and confirm the repair list is loop-free for the protected link or node failure. A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence.
C:Allocate routable SRv6 locators and supported endpoint behaviors and design explicit interworking for differing SR data planes. 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.
Question 407
A Cisco service provider design review finds: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link. The team proposes: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure.
- 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.
- MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks.
Explanation
Correct Answer
C:Demonstrable success requires: The steered flow crosses the required link and falls back safely if that adjacency is not available. Applied case: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link.
Incorrect Answers
A:TI-LFA computes a fast repair path using segment routing and a postconvergence viewpoint to avoid local loops after a topology failure. A node SID follows IGP shortest-path semantics, while an adjacency SID identifies a particular link local to its advertising router and must be reached in sequence.
B: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.
D:MPLS LSP ping and traceroute test labeled forwarding equivalence classes and can identify failures hidden behind successful IP control-plane checks. 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.
Question 408
The service provider operations team has not yet approved a change. Current evidence indicates: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link. 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.
- Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone.
- Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
- Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route.
Explanation
Correct Answer
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. Applied case: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link.
Incorrect Answers
A:This option addresses a different service provider engineering topic (RSVP TE fast reroute and local protection) rather than the documented SR adjacency SID and explicit segment list composition decision.
B:Inspect the active candidate, preference, BSID or policy steering rules, operational validity and flow path through the backbone. 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.
D:Compare MPLS echo replies, incoming and outgoing labels, FEC resolution and per-hop transport under the failed VPN route. 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.
Question 409
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link. 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 steered flow crosses the required link and falls back safely if that adjacency is not available.
- A valid LSP is signaled on capacity-feasible links and impossible reservations are rejected rather than silently oversubscribed.
- Traffic does not migrate onto the recovered path until a valid label-switched transport is available.
- Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation.
Explanation
Correct Answer
A: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. The result must be validated using the documented device, service or access context.
Incorrect Answers
B:This option addresses a different service provider engineering topic (RSVP-TE path signaling and reserved bandwidth) rather than the documented SR adjacency SID and explicit segment list composition decision.
C:Traffic does not migrate onto the recovered path until a valid label-switched transport is available. 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.
D:Each IPv6 segment resolves to its intended endpoint and traffic crosses SR-MPLS to SRv6 boundaries using supported adaptation. 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.
Question 410
For an original SPCOR service-provider engineering scenario, consider: A provider needs traffic to cross a specific parallel core link but its SR policy uses only the destination node SID, allowing normal ECMP to choose another link. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Change: Allocate unique intended prefix SID indexes and validate advertised SRGB information and effective labels on participating routers.
- Change: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
- Use only a destination node SID and promise deterministic traversal of a particular ECMP member without an adjacency segment.
- Check: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router.
- Check: Trace segment-list execution, SR label stack and the adjacency owner at each hop using a forced parallel-link test.
Explanation
Correct Answer
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. Acceptance: The steered flow crosses the required link and falls back safely if that adjacency is not available.
E: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. Required intervention: Combine node and adjacency SIDs in a segment list with proper endpoint locality and imposed stack depth for an explicit steering requirement.
Incorrect Answers
A:This option addresses a different service provider engineering topic (SR-MPLS prefix SID allocation and consistency) rather than the documented SR adjacency SID and explicit segment list composition decision.
C:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. 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.
D:Check: Compare IGP interface cost and SPF route, LDP session progress and LFIB entries during link bounce on each core router. 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.
