Question 270 An operator confuses a label-switched path with a VPN routing table and expects a transport LSP alone to prevent one customer's traffic from reaching another. Which technical mechanism best explains the behavior observed in this scenario? Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. A complete LSP needs continuous label switching across the intended MPLS-capable path. LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. ExplanationCorrect Answer B:A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. This explains why the initial condition produces the observed failure. The direct repair is: Separate transport label delivery from VPN service isolation and validate the applicable VRF/service labels. Validate through: Trace outer transport forwarding and the distinct customer-specific forwarding context at ingress and egress. Other Answers A:Label forwarding for a FEC commonly follows the underlay next-hop decision, so IGP metric changes can alter the LSP. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. C:A complete LSP needs continuous label switching across the intended MPLS-capable path. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. D:LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms.
Question 271 An operator confuses a label-switched path with a VPN routing table and expects a transport LSP alone to prevent one customer's traffic from reaching another. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Verify FEC reachability in the underlay and the corresponding LDP label binding. Inspect the assigned incoming label and associated label operation on the failing LSR. Trace outer transport forwarding and the distinct customer-specific forwarding context at ingress and egress. Compare incoming and outgoing labels at intermediate routers and observe delivery at the final egress. ExplanationCorrect Answer C:Trace outer transport forwarding and the distinct customer-specific forwarding context at ingress and egress. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. Other Answers A:Verify FEC reachability in the underlay and the corresponding LDP label binding. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. B:Inspect the assigned incoming label and associated label operation on the failing LSR. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. D:Compare incoming and outgoing labels at intermediate routers and observe delivery at the final egress. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms.
Question 272 An operator confuses a label-switched path with a VPN routing table and expects a transport LSP alone to prevent one customer's traffic from reaching another. Which lasting design or operational safeguard best prevents this particular issue from recurring? Teach per-hop label significance in operations runbooks and packet-trace procedures. Document the label stack and per-hop switching behavior in provider path troubleshooting. Monitor label distribution and LFIB consistency whenever core interfaces or protocols change. Document transport-versus-service labels in carrier design reviews. ExplanationCorrect Answer D:Document transport-versus-service labels in carrier design reviews. This addresses the recurring cause: A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. A targeted acceptance check is: Trace outer transport forwarding and the distinct customer-specific forwarding context at ingress and egress. Other Answers A:Teach per-hop label significance in operations runbooks and packet-trace procedures. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. B:Document the label stack and per-hop switching behavior in provider path troubleshooting. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. C:Monitor label distribution and LFIB consistency whenever core interfaces or protocols change. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms.
Question 273 The same incoming label number appears on two different core routers and a junior engineer reports a collision. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Validate each router's local label binding and adjacency rather than demanding one network-wide numeric label. Restore routability and required LDP discovery/transport reachability to the peer's label-space identifier. 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. ExplanationCorrect Answer A:Validate each router's local label binding and adjacency rather than demanding one network-wide numeric label. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. Inspect each hop's local incoming/outgoing label mapping and verify end-to-end continuity. Other Answers B:Restore routability and required LDP discovery/transport reachability to the peer's label-space identifier. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. C:Trace FEC next-hop selection in the underlay and align the core routing metric with the desired path. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. D:Recognize penultimate-hop popping and verify that the egress receives the intended remaining header or payload. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers.
Question 274 The same incoming label number appears on two different core routers and a junior engineer reports a collision. Which technical mechanism best explains the behavior observed in this scenario? A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. LDP signaling requires compatible peer discovery and transport connectivity beyond plain data-plane link state. ExplanationCorrect Answer B:MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. This explains why the initial condition produces the observed failure. The direct repair is: Validate each router's local label binding and adjacency rather than demanding one network-wide numeric label. Validate through: Inspect each hop's local incoming/outgoing label mapping and verify end-to-end continuity. Other Answers A:A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. C:LDP label bindings rely on reachable forwarding-equivalence classes and usable transport reachability. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. D:LDP signaling requires compatible peer discovery and transport connectivity beyond plain data-plane link state. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers.
Question 275 The same incoming label number appears on two different core routers and a junior engineer reports a collision. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Verify FEC reachability in the underlay and the corresponding LDP label binding. Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. Inspect each hop's local incoming/outgoing label mapping and verify end-to-end continuity. Capture or inspect LFIB pop operation at the penultimate node and successful delivery to egress. ExplanationCorrect Answer C:Inspect each hop's local incoming/outgoing label mapping and verify end-to-end continuity. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. Other Answers A:Verify FEC reachability in the underlay and the corresponding LDP label binding. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. B:Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. D:Capture or inspect LFIB pop operation at the penultimate node and successful delivery to egress. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers.
Question 276 The same incoming label number appears on two different core routers and a junior engineer reports a collision. Which lasting design or operational safeguard best prevents this particular issue from recurring? Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. Review label path impact when making IGP cost engineering changes. Document the label stack and per-hop switching behavior in provider path troubleshooting. Teach per-hop label significance in operations runbooks and packet-trace procedures. ExplanationCorrect Answer D:Teach per-hop label significance in operations runbooks and packet-trace procedures. This addresses the recurring cause: MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. A targeted acceptance check is: Inspect each hop's local incoming/outgoing label mapping and verify end-to-end continuity. Other Answers A:Use stable, reachable MPLS/LDP router IDs and validate them in maintenance windows. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. B:Review label path impact when making IGP cost engineering changes. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. C:Document the label stack and per-hop switching behavior in provider path troubleshooting. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers.
Question 277 A new IPv4 core path forwards plain IP but fails a labeled service because MPLS is not enabled on an intermediate transit link. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Enable or repair the supported MPLS forwarding and label-distribution configuration on the missing core link. Investigate the missing LFIB label binding or LSP continuity before changing customer IP routes. Repair IGP reachability to the required loopback and FEC before troubleshooting service labels. Trace the label-switched path and forwarding-label entries instead of assuming repeated customer-IP lookups in the core. ExplanationCorrect Answer A:Enable or repair the supported MPLS forwarding and label-distribution configuration on the missing core link. A complete LSP needs continuous label switching across the intended MPLS-capable path. Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. Other Answers B:Investigate the missing LFIB label binding or LSP continuity before changing customer IP routes. A complete LSP needs continuous label switching across the intended MPLS-capable path. C:Repair IGP reachability to the required loopback and FEC before troubleshooting service labels. A complete LSP needs continuous label switching across the intended MPLS-capable path. D:Trace the label-switched path and forwarding-label entries instead of assuming repeated customer-IP lookups in the core. A complete LSP needs continuous label switching across the intended MPLS-capable path.
Question 278 A new IPv4 core path forwards plain IP but fails a labeled service because MPLS is not enabled on an intermediate transit link. Which technical mechanism best explains the behavior observed in this scenario? A labeled packet requires a usable incoming-label forwarding entry; an unrelated global IP route does not replace it. A complete LSP needs continuous label switching across the intended MPLS-capable path. A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. ExplanationCorrect Answer B:A complete LSP needs continuous label switching across the intended MPLS-capable path. This explains why the initial condition produces the observed failure. The direct repair is: Enable or repair the supported MPLS forwarding and label-distribution configuration on the missing core link. Validate through: Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. Other Answers A:A labeled packet requires a usable incoming-label forwarding entry; an unrelated global IP route does not replace it. A complete LSP needs continuous label switching across the intended MPLS-capable path. C:A transport LSP carries traffic through the MPLS core; VPN context and forwarding separation require service mechanisms. A complete LSP needs continuous label switching across the intended MPLS-capable path. D:MPLS labels are locally significant to a label-switching context, not globally unique identifiers for all routers. A complete LSP needs continuous label switching across the intended MPLS-capable path.
Question 279 A new IPv4 core path forwards plain IP but fails a labeled service because MPLS is not enabled on an intermediate transit link. 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. Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. Inspect the assigned incoming label and associated label operation on the failing LSR. ExplanationCorrect Answer C:Check per-hop MPLS interface state, LDP adjacency and LFIB entries across the whole path. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: A complete LSP needs continuous label switching across the intended MPLS-capable path. Other Answers A:Check LDP neighbors and the transport address reachability after correcting underlay routing. A complete LSP needs continuous label switching across the intended MPLS-capable path. B:Compare incoming and outgoing labels at intermediate routers and observe delivery at the final egress. A complete LSP needs continuous label switching across the intended MPLS-capable path. D:Inspect the assigned incoming label and associated label operation on the failing LSR. A complete LSP needs continuous label switching across the intended MPLS-capable path.
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.
