Question 280 A new IPv4 core path forwards plain IP but fails a labeled service because MPLS is not enabled on an intermediate transit link. Which lasting design or operational safeguard best prevents this particular issue from recurring? Document expected label-pop behavior and distinguish it from unexpected label loss. Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. Teach per-hop label significance in operations runbooks and packet-trace procedures. Require labeled-service path tests in every backbone circuit acceptance plan. ExplanationCorrect Answer D:Require labeled-service path tests in every backbone circuit acceptance plan. This addresses the recurring cause: A complete LSP needs continuous label switching across the intended MPLS-capable path. A targeted acceptance check is: Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. Other Answers A:Document expected label-pop behavior and distinguish it from unexpected label loss. A complete LSP needs continuous label switching across the intended MPLS-capable path. B:Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. A complete LSP needs continuous label switching across the intended MPLS-capable path. C:Teach per-hop label significance in operations runbooks and packet-trace procedures. A complete LSP needs continuous label switching across the intended MPLS-capable path.
Question 281 A core router unexpectedly sends a label-switched packet toward a suboptimal neighbor after a change to the IGP metric. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Trace FEC next-hop selection in the underlay and align the core routing metric with the desired path. Recognize penultimate-hop popping and verify that the egress receives the intended remaining header or payload. Trace the label-switched path and forwarding-label entries instead of assuming repeated customer-IP lookups in the core. Separate transport label delivery from VPN service isolation and validate the applicable VRF/service labels. ExplanationCorrect Answer A:Trace FEC next-hop selection in the underlay and align the core routing metric with the desired path. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. Compare IGP next hops and LFIB outgoing adjacency before and after the metric correction. Other Answers B:Recognize penultimate-hop popping and verify that the egress receives the intended remaining header or payload. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. C:Trace the label-switched path and forwarding-label entries instead of assuming repeated customer-IP lookups in the core. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. D:Separate transport label delivery from VPN service isolation and validate the applicable VRF/service labels. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP.
Question 282 A core router unexpectedly sends a label-switched packet toward a suboptimal neighbor after a change to the IGP metric. Which technical mechanism best explains the behavior observed in this scenario? LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. A complete LSP needs continuous label switching across the intended MPLS-capable path. MPLS core label-switching routers forward based on labels using swap, push or pop operations according to LFIB entries. ExplanationCorrect Answer B:Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. This explains why the initial condition produces the observed failure. The direct repair is: Trace FEC next-hop selection in the underlay and align the core routing metric with the desired path. Validate through: Compare IGP next hops and LFIB outgoing adjacency before and after the metric correction. Other Answers A:LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. C:A complete LSP needs continuous label switching across the intended MPLS-capable path. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. D:MPLS core label-switching routers forward based on labels using swap, push or pop operations according to LFIB entries. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP.
Question 283 A core router unexpectedly sends a label-switched packet toward a suboptimal neighbor after a change to the IGP metric. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Check LDP neighbors and the transport address reachability after correcting underlay routing. Compare incoming and outgoing labels at intermediate routers and observe delivery at the final egress. Compare IGP next hops and LFIB outgoing adjacency before and after the metric correction. Capture or inspect LFIB pop operation at the penultimate node and successful delivery to egress. ExplanationCorrect Answer C:Compare IGP next hops and LFIB outgoing adjacency before and after the metric correction. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. Other Answers A:Check LDP neighbors and the transport address reachability after correcting underlay routing. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. B:Compare incoming and outgoing labels at intermediate routers and observe delivery at the final egress. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. D:Capture or inspect LFIB pop operation at the penultimate node and successful delivery to egress. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP.
Question 284 A core router unexpectedly sends a label-switched packet toward a suboptimal neighbor after a change to the IGP metric. Which lasting design or operational safeguard best prevents this particular issue from recurring? Monitor label distribution and LFIB consistency whenever core interfaces or protocols change. Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. Document the label stack and per-hop switching behavior in provider path troubleshooting. Review label path impact when making IGP cost engineering changes. ExplanationCorrect Answer D:Review label path impact when making IGP cost engineering changes. This addresses the recurring cause: Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. A targeted acceptance check is: Compare IGP next hops and LFIB outgoing adjacency before and after the metric correction. Other Answers A:Monitor label distribution and LFIB consistency whenever core interfaces or protocols change. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. B:Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. C:Document the label stack and per-hop switching behavior in provider path troubleshooting. Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP.
Question 285 Two enterprises use the same RFC1918 prefix in a shared MPLS L3 VPN core, but their VPN routes are leaking into one customer's forwarding table. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Check VRF import/export route-target policy and remove the unintended cross-tenant import. Repair provider core reachability to the advertising PE's next hop before changing the CE route. Correct the intended export/import route-target association on the relevant PEs. Configure appropriate route-target policies; keep route distinguishers for VPN route uniqueness. ExplanationCorrect Answer A:Check VRF import/export route-target policy and remove the unintended cross-tenant import. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. Inspect the customer VRF route tables and prove only authorized route targets are imported. Other Answers B:Repair provider core reachability to the advertising PE's next hop before changing the CE route. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. C:Correct the intended export/import route-target association on the relevant PEs. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. D:Configure appropriate route-target policies; keep route distinguishers for VPN route uniqueness. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap.
Question 286 Two enterprises use the same RFC1918 prefix in a shared MPLS L3 VPN core, but their VPN routes are leaking into one customer's forwarding table. Which technical mechanism best explains the behavior observed in this scenario? MPLS VPN labels support traffic separation and forwarding context, not cryptographic confidentiality of the payload. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. Route distinguishers distinguish VPNv4 prefixes, while route targets control import/export membership. ExplanationCorrect Answer B:VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. This explains why the initial condition produces the observed failure. The direct repair is: Check VRF import/export route-target policy and remove the unintended cross-tenant import. Validate through: Inspect the customer VRF route tables and prove only authorized route targets are imported. Other Answers A:MPLS VPN labels support traffic separation and forwarding context, not cryptographic confidentiality of the payload. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. C:A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. D:Route distinguishers distinguish VPNv4 prefixes, while route targets control import/export membership. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap.
Question 287 Two enterprises use the same RFC1918 prefix in a shared MPLS L3 VPN core, but their VPN routes are leaking into one customer's forwarding table. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Validate separate encryption controls, such as an approved IPsec overlay, rather than treating label traces as security proof. Confirm VPNv4 routes and their extended communities appear between PE neighbors. Inspect the customer VRF route tables and prove only authorized route targets are imported. Verify VRF RIB, MP-BGP route next hop and label stack all the way to remote PE. ExplanationCorrect Answer C:Inspect the customer VRF route tables and prove only authorized route targets are imported. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. Other Answers A:Validate separate encryption controls, such as an approved IPsec overlay, rather than treating label traces as security proof. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. B:Confirm VPNv4 routes and their extended communities appear between PE neighbors. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. D:Verify VRF RIB, MP-BGP route next hop and label stack all the way to remote PE. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap.
Question 288 Two enterprises use the same RFC1918 prefix in a shared MPLS L3 VPN core, but their VPN routes are leaking into one customer's forwarding table. Which lasting design or operational safeguard best prevents this particular issue from recurring? Include VPN address-family and community carriage in PE-to-PE peering checklists. Document route distinguisher and route-target roles separately in service templates. Verify PE loopback reachability and transport labels as part of new VPN service turn-up. Manage route-target inventories and apply explicit route-leak approval controls. ExplanationCorrect Answer D:Manage route-target inventories and apply explicit route-leak approval controls. This addresses the recurring cause: VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. A targeted acceptance check is: Inspect the customer VRF route tables and prove only authorized route targets are imported. Other Answers A:Include VPN address-family and community carriage in PE-to-PE peering checklists. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. B:Document route distinguisher and route-target roles separately in service templates. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap. C:Verify PE loopback reachability and transport labels as part of new VPN service turn-up. VRF route-target import policy controls which VPNv4 routes enter each customer VRF, independent of prefix overlap.
Question 289 A PE router sees a VPNv4 route in MP-BGP, but the customer VRF does not import it because the advertised route target is different. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Correct the intended export/import route-target association on the relevant PEs. Repair provider core reachability to the advertising PE's next hop before changing the CE route. Trace the VPN route's next hop and service-label/transport-label resolution across the provider core. Check VRF import/export route-target policy and remove the unintended cross-tenant import. ExplanationCorrect Answer A:Correct the intended export/import route-target association on the relevant PEs. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. Inspect the VPNv4 route's extended communities and the destination VRF's import list. Other Answers B:Repair provider core reachability to the advertising PE's next hop before changing the CE route. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. C:Trace the VPN route's next hop and service-label/transport-label resolution across the provider core. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. D:Check VRF import/export route-target policy and remove the unintended cross-tenant import. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target.
Question 290 A PE router sees a VPNv4 route in MP-BGP, but the customer VRF does not import it because the advertised route target is different. Which technical mechanism best explains the behavior observed in this scenario? VPNv4 NLRI and its route-target information require the appropriate multiprotocol BGP address family. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. A VPNv4 route can be learned but unusable if its BGP next hop cannot be resolved to a transport LSP. Route distinguishers distinguish VPNv4 prefixes, while route targets control import/export membership. ExplanationCorrect Answer B:A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. This explains why the initial condition produces the observed failure. The direct repair is: Correct the intended export/import route-target association on the relevant PEs. Validate through: Inspect the VPNv4 route's extended communities and the destination VRF's import list. Other Answers A:VPNv4 NLRI and its route-target information require the appropriate multiprotocol BGP address family. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. C:A VPNv4 route can be learned but unusable if its BGP next hop cannot be resolved to a transport LSP. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target. D:Route distinguishers distinguish VPNv4 prefixes, while route targets control import/export membership. A VPN route can exist in the MP-BGP control plane without entering a VRF that does not import its route target.
