Question 540
After Starlight IP Services deploys MPLS-TE preemption priority to allow higher-priority reservation requests to displace lower-priority capacity commitments, the primary acceptance check passes (admission selects eligible reservations and preemption obeys intended priorities). What remaining operational risk should still be part of the design review?
- Strict hop constraints fail if an intermediate node or link becomes unavailable.
- Dual-stack label operation depends on platform feature compatibility.
- Missing labels can produce selective packet loss despite healthy routing.
- Preemption can interrupt displaced services and requires policy controls.
Explanation
Correct Answer
D:The relevant boundary of MPLS-TE preemption priority is that preemption can interrupt displaced services and requires policy controls. Passing the acceptance test does not eliminate this residual operational risk.
Incorrect Answers
A:This concern applies to RSVP TE explicit path in a different scenario where operators need to steer an MPLS TE tunnel over selected intermediate nodes rather than only IGP shortest path. For the deployed MPLS-TE preemption priority approach, the relevant caution is instead that preemption can interrupt displaced services and requires policy controls.
B:This concern applies to LDP address family transport in a different scenario where operators need to carry the intended labeled IPv4 transport prefixes consistently across a provider core. For the deployed MPLS-TE preemption priority approach, the relevant caution is instead that preemption can interrupt displaced services and requires policy controls.
C:This concern applies to LDP label binding verification in a different scenario where operators need to check the label binding for a specific IGP destination before enabling a VPN. For the deployed MPLS-TE preemption priority approach, the relevant caution is instead that preemption can interrupt displaced services and requires policy controls.
Question 541
Northstar Carrier must ensure a prefix segment index resolves to an MPLS label on every transit node. The operator is comparing several service-provider methods. Which design or control directly addresses that stated requirement?
- SRGB consistent index mapping
- SR label stack capacity
- LDP directly connected hello discovery
- LDP session protection
Explanation
Correct Answer
A:SRGB consistent index mapping matches this requirement: the team should advertise and interpret SRGB parameters correctly for each segment-routing node. A relevant outcome would be that segment identifiers resolve to the intended local labels and forward to the same destination.
Incorrect Answers
B:SR label stack capacity instead addresses a different condition: validate forwarding hardware can impose all required MPLS labels for an SR policy. It would instead require you to limit the SID stack to the platform-supported maximum or use policy simplification, not the stated goal to ensure a prefix segment index resolves to an MPLS label on every transit node.
C:LDP directly connected hello discovery instead addresses a different condition: form LDP adjacency on a provider core link carrying labeled traffic. It would instead require you to enable compatible LDP link discovery on both facing interfaces, not the stated goal to ensure a prefix segment index resolves to an MPLS label on every transit node.
D:LDP session protection instead addresses a different condition: keep an LDP peer session through a brief loss of direct link connectivity. It would instead require you to enable supported LDP session protection and targeted-hello retention, not the stated goal to ensure a prefix segment index resolves to an MPLS label on every transit node.
Question 542
At Orion Transit, the engineering change is approved for SRGB consistent index mapping. The specific goal is to ensure a prefix segment index resolves to an MPLS label on every transit node. Which implementation step belongs in this change plan?
- Limit the SID stack to the platform-supported maximum or use policy simplification.
- Advertise and interpret SRGB parameters correctly for each segment-routing node.
- Enable compatible LDP link discovery on both facing interfaces.
- Enable supported LDP session protection and targeted-hello retention.
Explanation
Correct Answer
B:Implementing SRGB consistent index mapping requires the operator to advertise and interpret SRGB parameters correctly for each segment-routing node. This makes the required goal testable using evidence that segment identifiers resolve to the intended local labels and forward to the same destination.
Incorrect Answers
A:The proposed step is for SR label stack capacity, whose purpose is to validate forwarding hardware can impose all required MPLS labels for an SR policy. It would not perform the necessary SRGB consistent index mapping operation: advertise and interpret SRGB parameters correctly for each segment-routing node.
C:The proposed step is for LDP directly connected hello discovery, whose purpose is to form LDP adjacency on a provider core link carrying labeled traffic. It would not perform the necessary SRGB consistent index mapping operation: advertise and interpret SRGB parameters correctly for each segment-routing node.
D:The proposed step is for LDP session protection, whose purpose is to keep an LDP peer session through a brief loss of direct link connectivity. It would not perform the necessary SRGB consistent index mapping operation: advertise and interpret SRGB parameters correctly for each segment-routing node.
Question 543
Meridian Networks has deployed SRGB consistent index mapping to ensure a prefix segment index resolves to an MPLS label on every transit node. The implementation step was to advertise and interpret SRGB parameters correctly for each segment-routing node. Which observation demonstrates that the requested service is working?
- The headend programs the entire label stack without hardware resource errors.
- Peer discovery identifies both LSRs and the LDP session reaches operational state.
- Segment identifiers resolve to the intended local labels and forward to the same destination.
- The label session remains established over alternate IP reachability during disruption.
Explanation
Correct Answer
C:For SRGB consistent index mapping, successful verification means that segment identifiers resolve to the intended local labels and forward to the same destination. That evidence directly tests whether the provider can ensure a prefix segment index resolves to an MPLS label on every transit node after deployment.
Incorrect Answers
A:The observation would verify SR label stack capacity under the separate requirement to validate forwarding hardware can impose all required MPLS labels for an SR policy. It does not demonstrate the needed SRGB consistent index mapping result: segment identifiers resolve to the intended local labels and forward to the same destination.
B:The observation would verify LDP directly connected hello discovery under the separate requirement to form LDP adjacency on a provider core link carrying labeled traffic. It does not demonstrate the needed SRGB consistent index mapping result: segment identifiers resolve to the intended local labels and forward to the same destination.
D:The observation would verify LDP session protection under the separate requirement to keep an LDP peer session through a brief loss of direct link connectivity. It does not demonstrate the needed SRGB consistent index mapping result: segment identifiers resolve to the intended local labels and forward to the same destination.
Question 544
While troubleshooting SRGB consistent index mapping at Kestrel Broadband, the intended acceptance outcome is still missing: segment identifiers resolve to the intended local labels and forward to the same destination. Which fault condition should be investigated first for this particular design?
- An explicit SR path is configured with more imposed labels than hardware supports.
- IP routing works but LDP hellos are absent on the transport interface.
- The LDP session drops solely because direct hello adjacency disappeared.
- A global prefix SID index is assumed to mean an identical label on mismatched SRGB nodes.
Explanation
Correct Answer
D:The suspected defect directly frustrates SRGB consistent index mapping: a global prefix SID index is assumed to mean an identical label on mismatched SRGB nodes. Correcting it should allow verification that segment identifiers resolve to the intended local labels and forward to the same destination.
Incorrect Answers
A:This defect belongs to SR label stack capacity, where the affected outcome is to validate forwarding hardware can impose all required MPLS labels for an SR policy. It is not the direct failure mode identified for the SRGB consistent index mapping design in this case: a global prefix SID index is assumed to mean an identical label on mismatched SRGB nodes.
B:This defect belongs to LDP directly connected hello discovery, where the affected outcome is to form LDP adjacency on a provider core link carrying labeled traffic. It is not the direct failure mode identified for the SRGB consistent index mapping design in this case: a global prefix SID index is assumed to mean an identical label on mismatched SRGB nodes.
C:This defect belongs to LDP session protection, where the affected outcome is to keep an LDP peer session through a brief loss of direct link connectivity. It is not the direct failure mode identified for the SRGB consistent index mapping design in this case: a global prefix SID index is assumed to mean an identical label on mismatched SRGB nodes.
Question 545
After Harbor Metro deploys SRGB consistent index mapping to ensure a prefix segment index resolves to an MPLS label on every transit node, the primary acceptance check passes (segment identifiers resolve to the intended local labels and forward to the same destination). What remaining operational risk should still be part of the design review?
- SRGB differences require correct label translation at intermediate hops.
- Maximum stack depth differs among hardware and software implementations.
- Label distribution depends on working IGP reachability for mapped prefixes.
- Protection timers and backup IP path availability bound continuity.
Explanation
Correct Answer
A:The relevant boundary of SRGB consistent index mapping is that SRGB differences require correct label translation at intermediate hops. Passing the acceptance test does not eliminate this residual operational risk.
Incorrect Answers
B:This concern applies to SR label stack capacity in a different scenario where operators need to validate forwarding hardware can impose all required MPLS labels for an SR policy. For the deployed SRGB consistent index mapping approach, the relevant caution is instead that SRGB differences require correct label translation at intermediate hops.
C:This concern applies to LDP directly connected hello discovery in a different scenario where operators need to form LDP adjacency on a provider core link carrying labeled traffic. For the deployed SRGB consistent index mapping approach, the relevant caution is instead that SRGB differences require correct label translation at intermediate hops.
D:This concern applies to LDP session protection in a different scenario where operators need to keep an LDP peer session through a brief loss of direct link connectivity. For the deployed SRGB consistent index mapping approach, the relevant caution is instead that SRGB differences require correct label translation at intermediate hops.
Question 546
Summit Service Provider must steer a segment-routed packet to a particular node along its IGP shortest path. The operator is comparing several service-provider methods. Which design or control directly addresses that stated requirement?
- SRv6 VPN decapsulation
- node prefix SID forwarding
- MPLS label forwarding fault isolation
- CBTS tunnel service assignment
Explanation
Correct Answer
B:node prefix SID forwarding matches this requirement: the team should use the node's advertised prefix SID in the appropriate segment list. A relevant outcome would be that the packet reaches the node according to the node-SID shortest-path behavior.
Incorrect Answers
A:SRv6 VPN decapsulation instead addresses a different condition: deliver SRv6-encapsulated VPN traffic into the correct customer routing table. It would instead require you to use a suitable End.DT4 or End.DT6 service SID on the egress PE, not the stated goal to steer a segment-routed packet to a particular node along its IGP shortest path.
C:MPLS label forwarding fault isolation instead addresses a different condition: localize loss along a labeled transport LSP rather than at a customer application. It would instead require you to use MPLS OAM echo or traceroute along the intended forwarding equivalence class, not the stated goal to steer a segment-routed packet to a particular node along its IGP shortest path.
D:CBTS tunnel service assignment instead addresses a different condition: steer traffic classes over traffic-engineered tunnels according to service treatment. It would instead require you to classify flows and apply class-based tunnel selection for the supported forwarding policy, not the stated goal to steer a segment-routed packet to a particular node along its IGP shortest path.
Question 547
At Ridgeway Networks, the engineering change is approved for node prefix SID forwarding. The specific goal is to steer a segment-routed packet to a particular node along its IGP shortest path. Which implementation step belongs in this change plan?
- Use a suitable End.DT4 or End.DT6 service SID on the egress PE.
- Use MPLS OAM echo or traceroute along the intended forwarding equivalence class.
- Use the node's advertised prefix SID in the appropriate segment list.
- Classify flows and apply class-based tunnel selection for the supported forwarding policy.
Explanation
Correct Answer
C:Implementing node prefix SID forwarding requires the operator to use the node's advertised prefix SID in the appropriate segment list. This makes the required goal testable using evidence that the packet reaches the node according to the node-SID shortest-path behavior.
Incorrect Answers
A:The proposed step is for SRv6 VPN decapsulation, whose purpose is to deliver SRv6-encapsulated VPN traffic into the correct customer routing table. It would not perform the necessary node prefix SID forwarding operation: use the node's advertised prefix SID in the appropriate segment list.
B:The proposed step is for MPLS label forwarding fault isolation, whose purpose is to localize loss along a labeled transport LSP rather than at a customer application. It would not perform the necessary node prefix SID forwarding operation: use the node's advertised prefix SID in the appropriate segment list.
D:The proposed step is for CBTS tunnel service assignment, whose purpose is to steer traffic classes over traffic-engineered tunnels according to service treatment. It would not perform the necessary node prefix SID forwarding operation: use the node's advertised prefix SID in the appropriate segment list.
Question 548
Lakeside Transport has deployed node prefix SID forwarding to steer a segment-routed packet to a particular node along its IGP shortest path. The implementation step was to use the node's advertised prefix SID in the appropriate segment list. Which observation demonstrates that the requested service is working?
- Decapsulated traffic is looked up in the correct customer VRF.
- OAM results show which labeled hop first fails or misforwards traffic.
- Premium and best-effort classes follow their intended TE tunnels.
- The packet reaches the node according to the node-SID shortest-path behavior.
Explanation
Correct Answer
D:For node prefix SID forwarding, successful verification means that the packet reaches the node according to the node-SID shortest-path behavior. That evidence directly tests whether the provider can steer a segment-routed packet to a particular node along its IGP shortest path after deployment.
Incorrect Answers
A:The observation would verify SRv6 VPN decapsulation under the separate requirement to deliver SRv6-encapsulated VPN traffic into the correct customer routing table. It does not demonstrate the needed node prefix SID forwarding result: the packet reaches the node according to the node-SID shortest-path behavior.
B:The observation would verify MPLS label forwarding fault isolation under the separate requirement to localize loss along a labeled transport LSP rather than at a customer application. It does not demonstrate the needed node prefix SID forwarding result: the packet reaches the node according to the node-SID shortest-path behavior.
C:The observation would verify CBTS tunnel service assignment under the separate requirement to steer traffic classes over traffic-engineered tunnels according to service treatment. It does not demonstrate the needed node prefix SID forwarding result: the packet reaches the node according to the node-SID shortest-path behavior.
Question 549
While troubleshooting node prefix SID forwarding at Coastal Communications, the intended acceptance outcome is still missing: the packet reaches the node according to the node-SID shortest-path behavior. Which fault condition should be investigated first for this particular design?
- An adjacency SID is chosen expecting globally shortest-path node reachability.
- A transit End SID is used expecting to select a customer VRF automatically.
- Only ordinary host ping is used to assert every MPLS transit hop is correct.
- All classes remain on a single default tunnel despite distinct path requirement.
Explanation
Correct Answer
A:The suspected defect directly frustrates node prefix SID forwarding: an adjacency SID is chosen expecting globally shortest-path node reachability. Correcting it should allow verification that the packet reaches the node according to the node-SID shortest-path behavior.
Incorrect Answers
B:This defect belongs to SRv6 VPN decapsulation, where the affected outcome is to deliver SRv6-encapsulated VPN traffic into the correct customer routing table. It is not the direct failure mode identified for the node prefix SID forwarding design in this case: an adjacency SID is chosen expecting globally shortest-path node reachability.
C:This defect belongs to MPLS label forwarding fault isolation, where the affected outcome is to localize loss along a labeled transport LSP rather than at a customer application. It is not the direct failure mode identified for the node prefix SID forwarding design in this case: an adjacency SID is chosen expecting globally shortest-path node reachability.
D:This defect belongs to CBTS tunnel service assignment, where the affected outcome is to steer traffic classes over traffic-engineered tunnels according to service treatment. It is not the direct failure mode identified for the node prefix SID forwarding design in this case: an adjacency SID is chosen expecting globally shortest-path node reachability.
Question 550
After Bluebird Infrastructure deploys node prefix SID forwarding to steer a segment-routed packet to a particular node along its IGP shortest path, the primary acceptance check passes (the packet reaches the node according to the node-SID shortest-path behavior). What remaining operational risk should still be part of the design review?
- VRF security isolation depends on correctly assigned service SIDs.
- Node SID path still follows IGP state and can change after failures.
- Some platforms and security policies constrain MPLS OAM replies.
- Fallback behavior matters if a class-specific tunnel becomes unavailable.
Explanation
Correct Answer
B:The relevant boundary of node prefix SID forwarding is that node SID path still follows IGP state and can change after failures. Passing the acceptance test does not eliminate this residual operational risk.
Incorrect Answers
A:This concern applies to SRv6 VPN decapsulation in a different scenario where operators need to deliver SRv6-encapsulated VPN traffic into the correct customer routing table. For the deployed node prefix SID forwarding approach, the relevant caution is instead that node SID path still follows IGP state and can change after failures.
C:This concern applies to MPLS label forwarding fault isolation in a different scenario where operators need to localize loss along a labeled transport LSP rather than at a customer application. For the deployed node prefix SID forwarding approach, the relevant caution is instead that node SID path still follows IGP state and can change after failures.
D:This concern applies to CBTS tunnel service assignment in a different scenario where operators need to steer traffic classes over traffic-engineered tunnels according to service treatment. For the deployed node prefix SID forwarding approach, the relevant caution is instead that node SID path still follows IGP state and can change after failures.
Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) (350-501) Practice Tests