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This option proposes: IGMP reports express receiver interest in multicast groups and a querier maintains group membership state; without appropriate reports or queries a router can age out forwarding toward a segment. It addresses the different topic IGMP querier membership reports and group timeout, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Passive OSPF interfaces can stop unwanted neighbor discovery while their connected networks may still be advertised through the OSPF process; authentication protects routing exchanges and requires compatible peer settings. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: An OSPF ASBR originates type 5 external LSAs in eligible areas; E1 metrics account for internal cost toward the ASBR, whereas E2 selection prioritizes external cost except for applicable tie-breakers. It addresses the different topic OSPF external LSAs and E1 versus E2 cost, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Compare each candidate path's per-interface costs, SPF route metrics, topology database and resulting next-hop entries. It addresses the different topic OSPF SPF calculation and interface cost changes, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Inspect all routers' area flags, ABR default LSA advertisement, permitted LSA types and whether an ASBR is incorrectly placed in the area. It addresses the different topic Stub and totally stub area restrictions, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Inspect classifier match counters, behavior actions, traffic-policy associations, interface attachment and ingress/egress direction. It addresses the different topic Huawei MQC traffic classification and behavior binding, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

That option concerns OSPF summarization at ABR and ASBR. That follows from the targeted action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

That option concerns IS-IS area addresses and adjacency prerequisites. That follows from the targeted action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

That option concerns NSSA type seven translation and default routing. That follows from the targeted action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

This option proposes: Troubleshoot BGP establishment by distinguishing TCP port 179 transport, peer configuration and OPEN capability negotiation. It addresses the different topic BGP transport reachability and session states, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Check DR and BDR addresses, each neighbor's interface priority and router ID, network type and whether an election actually occurred. It addresses the different topic OSPF broadcast DR and BDR election, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Choose the appropriate enterprise datacom architecture for a campus user edge versus a scalable data-center fabric before selecting a particular routing or switching feature. It addresses the different topic Campus design versus data center fabric operational boundaries, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (A growing enterprise introduces area 40 that connects only through area 20, and prefixes are inconsistent because area 0 is not properly joined.).

This option proposes: Diagnose an unexpected OSPF intra-area path by comparing cumulative interface costs through the shortest-path tree. It addresses the different topic OSPF SPF calculation and interface cost changes, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Trace PIM-SM receiver joins toward an RP and subsequent shortest-path behavior when investigating delayed or suboptimal multicast. It addresses the different topic PIM sparse mode RP shared tree and shortest path transition, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Compare OSPF interface state, area, authentication, timers and network type before resetting a neighbor relationship. It addresses the different topic OSPF adjacency prerequisites and mismatched parameters, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: A stub area blocks type 5 external LSAs and receives an appropriate default through its ABR; a totally stubby configuration additionally suppresses most inter-area summaries and is incompatible with certain topology roles. It addresses the different topic Stub and totally stub area restrictions, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Routing protocols and static configuration contribute candidate routes to the routing information base, while the forwarding information base contains resolved next-hop and interface data used to forward packets. It addresses the different topic Network forwarding planes RIB versus FIB, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: On a broadcast network OSPF uses a DR and BDR to limit adjacency overhead; priority zero excludes a candidate, and higher eligible priority and router ID influence a new election rather than forcing instant replacement of a functioning DR. It addresses the different topic OSPF broadcast DR and BDR election, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Review manager IP, user security level, permissions, device trap destination, authentication logs and sample interface counters or link-down notifications. It addresses the different topic SNMP manager polling traps and authenticated operation, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Trace the NSSA ASBR's type 7 LSA, translator ABR status, resulting type 5 advertisement outside the area and any intentionally configured default. It addresses the different topic NSSA type seven translation and default routing, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Check whether the interface should form neighbors, its authentication mode, passive state, advertised prefix and neighboring device visibility. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

That option concerns OSPF external LSAs and E1 versus E2 cost. That follows from the targeted Recommended action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

That option concerns NSSA type seven translation and default routing. That follows from the targeted Recommended action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

That option concerns SDN WAN control and SD-WAN policy forwarding. That follows from the targeted Recommended action: Evaluate non-backbone OSPF connectivity through area 0 and whether a virtual link is an appropriate temporary correction in supported topologies.

This option proposes: Assume adding an arbitrary BGP community automatically blocks a route from every router on the Internet without any peer-side policy or recognized well-known meaning. It addresses the different topic BGP community tagging and route-policy control, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Enable OSPF neighbor formation on an untrusted user access VLAN because route advertisement is presumed impossible without forming user-device adjacencies. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Configure a stub area on only one side of an OSPF adjacency and insist that an external type 5 LSA must cross that boundary unchanged. It addresses the different topic Stub and totally stub area restrictions, not the directly tested OSPF backbone connectivity and virtual link design failure in the stated incident (An engineer proposes a virtual link to bridge a divided OSPF backbone but overlooks that the chosen transit area was configured as totally stub.).

This option proposes: Distinguish redistributed external routes and external cost types when diagnosing a route that enters through an ASBR. It addresses the different topic OSPF external LSAs and E1 versus E2 cost, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).

This option proposes: Use AS_PATH to reason about external route propagation, loop prevention and intentional prepending effects. It addresses the different topic BGP AS_PATH path-vector loop prevention, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).

This option proposes: Compare OSPF interface state, area, authentication, timers and network type before resetting a neighbor relationship. It addresses the different topic OSPF adjacency prerequisites and mismatched parameters, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).

This option proposes: On a broadcast network OSPF uses a DR and BDR to limit adjacency overhead; priority zero excludes a candidate, and higher eligible priority and router ID influence a new election rather than forcing instant replacement of a functioning DR. It addresses the different topic OSPF broadcast DR and BDR election, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).

This option proposes: An NSSA permits its local ASBR to originate type 7 external LSAs that can be translated to type 5 by an eligible ABR, while incoming external type 5 advertisements are not flooded into the NSSA. It addresses the different topic NSSA type seven translation and default routing, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).

This option proposes: MED is an optional nontransitive BGP attribute, with lower values typically favored when compared under applicable rules; it is often compared for routes from the same neighboring AS unless policy changes this behavior. It addresses the different topic BGP MED interpretation between neighboring autonomous systems, not the directly tested OSPF SPF calculation and interface cost changes failure in the stated incident (A campus core prefers a three-link path over a direct uplink because the direct link's OSPF cost was raised for maintenance.).