Question 430 A router's IPv4 ACL has permit statements for two user networks but silently drops DNS replies from a third required subnet. Which technical mechanism best explains the behavior observed in this scenario? uRPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. ExplanationCorrect Answer B:The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. This explains why the initial condition produces the observed failure. The direct repair is: Add a narrowly scoped permit for the authorized DNS traffic before the implicit deny. Validate through: Inspect ACE hit counts and verify only the intended DNS exchange now passes. Other Answers A:URPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. C:IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. D:A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit.
Question 431 A router's IPv4 ACL has permit statements for two user networks but silently drops DNS replies from a third required subnet. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Use packet-path tracing and ACE counters to show the target flow actually encounters the policy. Inspect running policy and counters for representative new addresses after deployment. Inspect ACE hit counts and verify only the intended DNS exchange now passes. Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. ExplanationCorrect Answer C:Inspect ACE hit counts and verify only the intended DNS exchange now passes. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. Other Answers A:Use packet-path tracing and ACE counters to show the target flow actually encounters the policy. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. B:Inspect running policy and counters for representative new addresses after deployment. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. D:Compare reverse-route lookup with ingress interface and confirm authorized asymmetric traffic passes after correction. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit.
Question 432 A router's IPv4 ACL has permit statements for two user networks but silently drops DNS replies from a third required subnet. Which lasting design or operational safeguard best prevents this particular issue from recurring? Map interface/direction placement to forwarding paths during every ACL change. Use ordered exception reviews and negative tests before ACL deployment. Monitor source-prefix reachability alongside ingress anti-spoofing drops. Track required applications and implicit-deny cases in ACL policy matrices. ExplanationCorrect Answer D:Track required applications and implicit-deny cases in ACL policy matrices. This addresses the recurring cause: The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. A targeted acceptance check is: Inspect ACE hit counts and verify only the intended DNS exchange now passes. Other Answers A:Map interface/direction placement to forwarding paths during every ACL change. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. B:Use ordered exception reviews and negative tests before ACL deployment. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit. C:Monitor source-prefix reachability alongside ingress anti-spoofing drops. The end of an IPv4 ACL has an implicit deny for packets not matching any earlier permit.
Question 433 A standard ACL applied outbound on a shared WAN interface blocks a server subnet that should be allowed, but it cannot distinguish application ports. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Use an appropriately placed extended ACL that matches source, destination and required transport ports. Verify the actual traffic ingress path and apply the policy to the correct interface and direction. Trace each applied ACL and relevant control-plane policy along the actual packet path rather than expanding the local permit. Evaluate feasible or loose uRPF mode and source-prefix policy against the approved asymmetric topology. ExplanationCorrect Answer A:Use an appropriately placed extended ACL that matches source, destination and required transport ports. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. Verify the intended server application passes and an unauthorized source/port pair still fails. Other Answers B:Verify the actual traffic ingress path and apply the policy to the correct interface and direction. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. C:Trace each applied ACL and relevant control-plane policy along the actual packet path rather than expanding the local permit. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. D:Evaluate feasible or loose uRPF mode and source-prefix policy against the approved asymmetric topology. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields.
Question 434 A standard ACL applied outbound on a shared WAN interface blocks a server subnet that should be allowed, but it cannot distinguish application ports. Which technical mechanism best explains the behavior observed in this scenario? IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. Cisco ACL entries are evaluated in order and processing stops at the first match. uRPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. ExplanationCorrect Answer B:A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. This explains why the initial condition produces the observed failure. The direct repair is: Use an appropriately placed extended ACL that matches source, destination and required transport ports. Validate through: Verify the intended server application passes and an unauthorized source/port pair still fails. Other Answers A:IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. C:Cisco ACL entries are evaluated in order and processing stops at the first match. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. D:URPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields.
Question 435 A standard ACL applied outbound on a shared WAN interface blocks a server subnet that should be allowed, but it cannot distinguish application ports. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. 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. Inspect running policy and counters for representative new addresses after deployment. ExplanationCorrect Answer C:Verify the intended server application passes and an unauthorized source/port pair still fails. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. Other Answers A:Inspect source RIB entry, interface uRPF counters and accepted customer packets after route recovery. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. B:Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. D:Inspect running policy and counters for representative new addresses after deployment. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields.
Question 436 A standard ACL applied outbound on a shared WAN interface blocks a server subnet that should be allowed, but it cannot distinguish application ports. Which lasting design or operational safeguard best prevents this particular issue from recurring? Review IPv4 and IPv6 filters together in dual-stack hardening checks. Track required applications and implicit-deny cases in ACL policy matrices. Map interface/direction placement to forwarding paths during every ACL change. Choose ACL type and placement according to the fields required by the security decision. ExplanationCorrect Answer D:Choose ACL type and placement according to the fields required by the security decision. This addresses the recurring cause: A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. A targeted acceptance check is: Verify the intended server application passes and an unauthorized source/port pair still fails. Other Answers A:Review IPv4 and IPv6 filters together in dual-stack hardening checks. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. B:Track required applications and implicit-deny cases in ACL policy matrices. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields. C:Map interface/direction placement to forwarding paths during every ACL change. A standard IPv4 ACL matches source addressing only, while extended ACLs can match more packet fields.
Question 437 A router interface accepts IPv6 SSH from a maintenance host even though the team configured an IPv4 ACL denying its IPv4 equivalent. Which corrective action most directly resolves the documented failure without suppressing unrelated safeguards? Apply a properly scoped IPv6 traffic-filter policy to the correct interface and direction. Use an appropriately placed extended ACL that matches source, destination and required transport ports. Correct and synchronize device time and validate the referenced time-range configuration. Verify feature support and compile an equivalent explicit supported ACE policy for the device release. ExplanationCorrect Answer A:Apply a properly scoped IPv6 traffic-filter policy to the correct interface and direction. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Other Answers B:Use an appropriately placed extended ACL that matches source, destination and required transport ports. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. C:Correct and synchronize device time and validate the referenced time-range configuration. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. D:Verify feature support and compile an equivalent explicit supported ACE policy for the device release. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax.
Question 438 A router interface accepts IPv6 SSH from a maintenance host even though the team configured an IPv4 ACL denying its IPv4 equivalent. Which technical mechanism best explains the behavior observed in this scenario? uRPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. Cisco ACL entries are evaluated in order and processing stops at the first match. Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. ExplanationCorrect Answer B:IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. This explains why the initial condition produces the observed failure. The direct repair is: Apply a properly scoped IPv6 traffic-filter policy to the correct interface and direction. Validate through: Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Other Answers A:URPF depends on source-route lookup; losing a legitimate source route can make valid traffic fail reverse-path checks. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. C:Cisco ACL entries are evaluated in order and processing stops at the first match. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. D:Strict uRPF expects the reverse-path best route toward the source to use the receiving interface, so asymmetry can cause drops. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax.
Question 439 A router interface accepts IPv6 SSH from a maintenance host even though the team configured an IPv4 ACL denying its IPv4 equivalent. After applying the correction, which verification evidence most directly demonstrates that this issue is resolved? Check clock/timezone, active time range and backup traffic at the intended window. Inspect hit counters for the deny and permit ACEs and test HTTPS plus denied non-HTTPS traffic. Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. ExplanationCorrect Answer C:Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. This checks the affected traffic or control-plane behavior, not merely a generic up/down indicator. The underlying mechanism is: IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. Other Answers A:Check clock/timezone, active time range and backup traffic at the intended window. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. B:Inspect hit counters for the deny and permit ACEs and test HTTPS plus denied non-HTTPS traffic. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. D:Observe a permitted local ACL hit alongside a deny hit at the actual blocking policy. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax.
Question 440 A router interface accepts IPv6 SSH from a maintenance host even though the team configured an IPv4 ACL denying its IPv4 equivalent. Which lasting design or operational safeguard best prevents this particular issue from recurring? Use defined source-address allowlists and do not assume loose uRPF equals strict ingress validation. Use ordered exception reviews and negative tests before ACL deployment. Validate supported syntax and feature matrices before distributing common ACL templates. Review IPv4 and IPv6 filters together in dual-stack hardening checks. ExplanationCorrect Answer D:Review IPv4 and IPv6 filters together in dual-stack hardening checks. This addresses the recurring cause: IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. A targeted acceptance check is: Test IPv6 SSH from authorized and unauthorized hosts against IPv6 ACL counters. Other Answers A:Use defined source-address allowlists and do not assume loose uRPF equals strict ingress validation. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. B:Use ordered exception reviews and negative tests before ACL deployment. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax. C:Validate supported syntax and feature matrices before distributing common ACL templates. IPv4 ACLs do not filter IPv6 packets; IPv6 traffic needs separate IPv6 policy and matching syntax.
