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This option proposes: Packet selection uses the most-specific matching destination route before comparing candidate protocol preferences for identical prefixes; a broad default route does not displace a more-specific valid route solely by lower preference. It addresses the different topic Longest prefix match and route preferences, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: Inspect the community attached to a prefix, the matching community filter, permit or deny clauses and the route after policy application. It addresses the different topic BGP community tagging and route-policy control, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: All non-backbone areas have correct backbone-based connectivity, and any virtual link is explicitly understood as a constrained repair, not a generic shortcut. It addresses the different topic OSPF backbone connectivity and virtual link design, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: Routing adjacencies exist only on authorized transit links while user networks remain reachable as advertised prefixes. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: The Layer 2 domain forwards without loops and a documented alternate path transitions safely when the active root path fails. It addresses the different topic RSTP port roles and rapid convergence, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: Diagnose a multicast drop by checking reverse path forwarding against the packet's source rather than only validating the destination group. It addresses the different topic Multicast reverse path forwarding checks, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: Inspect the summarization boundary, contributing active component prefixes, aggregate advertisement and forwarding toward the actual destinations. It addresses the different topic OSPF summarization at ABR and ASBR, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (Two campus routers see one another's hello packets but remain in a non-Full state after an interface was moved into a different OSPF area.).

This option proposes: Choose OSPF summarization at the correct boundary and account for reachability when advertising aggregates. It addresses the different topic OSPF summarization at ABR and ASBR, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: Diagnose a packet-forwarding discrepancy by separating control-plane routes recorded in the RIB from hardware or software forwarding entries installed in the FIB. It addresses the different topic Network forwarding planes RIB versus FIB, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: OSPF's intra-area SPF calculation prefers the lowest valid accumulated link cost, subject to equal-cost rules; a protocol neighbor being Full alone does not establish path preference. It addresses the different topic OSPF SPF calculation and interface cost changes, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: STP and RSTP root election depends on bridge IDs and configured priorities, while root-path cost and port IDs help select forwarding roles; a device with more physical connections is not automatically elected root. It addresses the different topic RSTP designated root and backup topology selection, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: Compare bridge priority and MAC-derived IDs, root bridge identity, root-path costs and per-port selection on adjacent switches. It addresses the different topic RSTP designated root and backup topology selection, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

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 adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

That option concerns WLAN VLAN pools and DHCP address scopes. That follows from the targeted Recommended action: Compare OSPF interface state, area, authentication, timers and network type before resetting a neighbor relationship.

That option concerns Stub and totally stub area restrictions. That follows from the targeted Recommended action: Compare OSPF interface state, area, authentication, timers and network type before resetting a neighbor relationship.

That option concerns OSPF backbone connectivity and virtual link design. That follows from the targeted Recommended action: Compare OSPF interface state, area, authentication, timers and network type before resetting a neighbor relationship.

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 adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.). The better discriminating check for this case is: Inspect OSPF neighbor states and interface detail on both ends, including area IDs, hello/dead intervals, network type and authentication settings.

This option proposes: Examine per-VRF routing and interface membership before declaring two isolated customer networks mutually reachable. It addresses the different topic VRF traffic separation and route leaking controls, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: Validate IPv6 router advertisements, prefix information and duplicate-address detection before treating a newly generated address as usable. It addresses the different topic IPv6 SLAAC RA prefix and duplicate address detection, not the directly tested OSPF adjacency prerequisites and mismatched parameters failure in the stated incident (A branch migration changes OSPF authentication on one router only, and operations sees repeated neighbor down events although physical links remain up.).

This option proposes: Check OSPF area type before attempting to import external routes into an area intended to suppress route detail. It addresses the different topic Stub and totally stub area restrictions, not the directly tested OSPF broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).

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 broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).

This option proposes: Check the MED value and the policy context before using BGP advertisements to suggest which entry link another AS should prefer. It addresses the different topic BGP MED interpretation between neighboring autonomous systems, not the directly tested OSPF broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).

This option proposes: Inter-area OSPF design relies on a connected backbone area; virtual links can logically connect certain disconnected backbone segments through a suitable transit area but cannot pass through a stub area. It addresses the different topic OSPF backbone connectivity and virtual link design, not the directly tested OSPF broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).

This option proposes: VRRP uses a virtual router identity and virtual MAC per IPv4 group to preserve a stable next-hop identity across master changes; correct failover still requires matching VLAN, neighbor learning and eligible router state. It addresses the different topic VRRP virtual MAC and endpoint ARP continuity, not the directly tested OSPF broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).

This option proposes: OSPF's intra-area SPF calculation prefers the lowest valid accumulated link cost, subject to equal-cost rules; a protocol neighbor being Full alone does not establish path preference. It addresses the different topic OSPF SPF calculation and interface cost changes, not the directly tested OSPF broadcast DR and BDR election failure in the stated incident (A switch segment receives a new OSPF speaker with a high priority, but its dashboard still shows the long-running designated router.).