Question 450 An extended ACL with a permit for TCP destination port 22 cannot pass SSH because another policy earlier on the path denies the same connection. Which technical mechanism best explains the behavior observed in this scenario? Interface ACLs inspect packets only as they cross the configured interface in the specified direction. An interface ACL permit does not override a deny at a different processing point or security layer. ACL object-group support and expansion depend on platform and software; unsupported constructs do not create intended matches. uRPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. ExplanationCorrect Answer B:An interface ACL permit does not override a deny at a different processing point or security layer. This explains why the initial condition produces the observed failure. The direct repair is: Trace each applied ACL and relevant control-plane policy along the actual packet path rather than expanding the local permit. Validate through: Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. Other Answers A:Interface ACLs inspect packets only as they cross the configured interface in the specified direction. An interface ACL permit does not override a deny at a different processing point or security layer. C:ACL object-group support and expansion depend on platform and software; unsupported constructs do not create intended matches. An interface ACL permit does not override a deny at a different processing point or security layer. D:URPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. An interface ACL permit does not override a deny at a different processing point or security layer.
Question 451 An extended ACL with a permit for TCP destination port 22 cannot pass SSH because another policy earlier on the path denies the same connection. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Inspect hit counters for the deny and permit ACEs and test HTTPS plus denied non-HTTPS traffic. Inspect running policy and counters for representative new addresses after deployment. Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. Verify the intended server application passes and an unauthorized source/port pair still fails. ExplanationCorrect Answer C:Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: An interface ACL permit does not override a deny at a different processing point or security layer. Other Answers A:Inspect hit counters for the deny and permit ACEs and test HTTPS plus denied non-HTTPS traffic. An interface ACL permit does not override a deny at a different processing point or security layer. B:Inspect running policy and counters for representative new addresses after deployment. An interface ACL permit does not override a deny at a different processing point or security layer. D:Verify the intended server application passes and an unauthorized source/port pair still fails. An interface ACL permit does not override a deny at a different processing point or security layer.
Question 452 An extended ACL with a permit for TCP destination port 22 cannot pass SSH because another policy earlier on the path denies the same connection. Which lasting design or operational safeguard best prevents this particular issue from recurring? Monitor source-prefix reachability alongside ingress anti-spoofing drops. Map interface/direction placement to forwarding paths during every ACL change. Include time synchronization monitoring for all time-dependent firewall and ACL policies. Maintain end-to-end access path diagrams and test overlapping controls together. ExplanationCorrect Answer D:Maintain end-to-end access path diagrams and test overlapping controls together. This addresses the recurring cause: An interface ACL permit does not override a deny at a different processing point or security layer. A targeted acceptance check is: Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. Other Answers A:Monitor source-prefix reachability alongside ingress anti-spoofing drops. An interface ACL permit does not override a deny at a different processing point or security layer. B:Map interface/direction placement to forwarding paths during every ACL change. An interface ACL permit does not override a deny at a different processing point or security layer. C:Include time synchronization monitoring for all time-dependent firewall and ACL policies. An interface ACL permit does not override a deny at a different processing point or security layer.
Question 453 Strict unicast RPF drops valid customer packets on an asymmetric dual-homed network whose best return route uses the other interface. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Evaluate feasible or loose uRPF mode and source-prefix policy against the approved asymmetric topology. Trace each applied ACL and relevant control-plane policy along the actual packet path rather than expanding the local permit. Verify feature support and compile an equivalent explicit supported ACE policy for the device release. Repair authorized reverse-route visibility and then verify uRPF before disabling spoofing protections globally. ExplanationCorrect Answer A:Evaluate feasible or loose uRPF mode and source-prefix policy against the approved asymmetric topology. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. Other Answers B:Trace each applied ACL and relevant control-plane policy along the actual packet path rather than expanding the local permit. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. C:Verify feature support and compile an equivalent explicit supported ACE policy for the device release. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. D:Repair authorized reverse-route visibility and then verify uRPF before disabling spoofing protections globally. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops.
Question 454 Strict unicast RPF drops valid customer packets on an asymmetric dual-homed network whose best return route uses the other interface. Which technical mechanism best explains the behavior observed in this scenario? ACL object-group support and expansion depend on platform and software; unsupported constructs do not create intended matches. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. ExplanationCorrect Answer B:Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. This explains why the initial condition produces the observed failure. The direct repair is: Evaluate feasible or loose uRPF mode and source-prefix policy against the approved asymmetric topology. Validate through: Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. Other Answers A:ACL object-group support and expansion depend on platform and software; unsupported constructs do not create intended matches. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. C:The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. D:A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops.
Question 455 Strict unicast RPF drops valid customer packets on an asymmetric dual-homed network whose best return route uses the other interface. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. Verify the intended server application passes and an unauthorized source/port pair still fails. ExplanationCorrect Answer C:Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. Other Answers A:Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. B:Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. D:Verify the intended server application passes and an unauthorized source/port pair still fails. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops.
Question 456 Strict unicast RPF drops valid customer packets on an asymmetric dual-homed network whose best return route uses the other interface. Which lasting design or operational safeguard best prevents this particular issue from recurring? Validate supported syntax and feature matrices before distributing common ACL templates. Review IPv4 and IPv6 filters together in dual-stack hardening checks. Use ordered exception reviews and negative tests before ACL deployment. Design spoofing protection around real routing asymmetry and test multiple ingress paths. ExplanationCorrect Answer D:Design spoofing protection around real routing asymmetry and test multiple ingress paths. This addresses the recurring cause: Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. A targeted acceptance check is: Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. Other Answers A:Validate supported syntax and feature matrices before distributing common ACL templates. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. B:Review IPv4 and IPv6 filters together in dual-stack hardening checks. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. C:Use ordered exception reviews and negative tests before ACL deployment. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops.
Question 457 Loose uRPF allows a packet because a broad default route exists, even though the network team expects to block a forged source. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Combine appropriate source-prefix filtering and platform-specific uRPF behavior rather than relying solely on default-route reachability. Repair authorized reverse-route visibility and then verify uRPF before disabling spoofing protections globally. Apply a properly scoped IPv6 traffic-filter policy to the correct interface and direction. Add a narrowly scoped permit for the authorized DNS traffic before the implicit deny. ExplanationCorrect Answer A:Combine appropriate source-prefix filtering and platform-specific uRPF behavior rather than relying solely on default-route reachability. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Other Answers B:Repair authorized reverse-route visibility and then verify uRPF before disabling spoofing protections globally. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. C:Apply a properly scoped IPv6 traffic-filter policy to the correct interface and direction. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. D:Add a narrowly scoped permit for the authorized DNS traffic before the implicit deny. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings.
Question 458 Loose uRPF allows a packet because a broad default route exists, even though the network team expects to block a forged source. Which technical mechanism best explains the behavior observed in this scenario? Interface ACLs inspect packets only as they cross the configured interface in the specified direction. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. Time-range ACL evaluation depends on the router's effective time settings as well as packet matching. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. ExplanationCorrect Answer B:Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. This explains why the initial condition produces the observed failure. The direct repair is: Combine appropriate source-prefix filtering and platform-specific uRPF behavior rather than relying solely on default-route reachability. Validate through: Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Other Answers A:Interface ACLs inspect packets only as they cross the configured interface in the specified direction. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. C:Time-range ACL evaluation depends on the router's effective time settings as well as packet matching. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. D:The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings.
Question 459 Loose uRPF allows a packet because a broad default route exists, even though the network team expects to block a forged source. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Check clock/timezone, active time range and backup traffic at the intended window. Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. ExplanationCorrect Answer C:Send controlled spoofed-source test packets and verify the explicit source filter blocks them. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. Other Answers A:Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. B:Check clock/timezone, active time range and backup traffic at the intended window. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. D:Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings.
Question 460 Loose uRPF allows a packet because a broad default route exists, even though the network team expects to block a forged source. Which lasting design or operational safeguard best prevents this particular issue from recurring? Validate supported syntax and feature matrices before distributing common ACL templates. Choose ACL type and placement according to the fields required by the security decision. Maintain end-to-end access path diagrams and test overlapping controls together. Use defined source-address allowlists and do not assume loose uRPF equals strict ingress validation. ExplanationCorrect Answer D:Use defined source-address allowlists and do not assume loose uRPF equals strict ingress validation. This addresses the recurring cause: Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. A targeted acceptance check is: Send controlled spoofed-source test packets and verify the explicit source filter blocks them. Other Answers A:Validate supported syntax and feature matrices before distributing common ACL templates. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. B:Choose ACL type and placement according to the fields required by the security decision. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings. C:Maintain end-to-end access path diagrams and test overlapping controls together. Loose uRPF checks that a route to the source exists; a default route may satisfy that criterion depending on implementation settings.
