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Aligning the OSPF hello and dead timers on the adjacency interfaces would not assign distinct stable router IDs and restart/clear the relevant OSPF process as required by the platform.

Interpreting DR/BDR election and normal DROther-to-DROther 2-Way behavior on broadcast networks would not assign distinct stable router IDs and restart/clear the relevant OSPF process as required by the platform.

Configuring the appropriate OSPF point-to-point network type on the dedicated link would not assign distinct stable router IDs and restart/clear the relevant OSPF process as required by the platform.

This test measures a different behavior: Verify no DR/BDR election and the peer reaches Full on the point-to-point interface. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check `show ip ospf neighbor` transitions to Full and peer router IDs are unique.

This test measures a different behavior: Compare interface timer fields in OSPF show output and verify neighbors reach Full. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check `show ip ospf neighbor` transitions to Full and peer router IDs are unique.

This test measures a different behavior: Check that both DROthers form Full adjacency to the designated router or backup router as appropriate. It does not establish the target outcome. For the documented fault, the direct acceptance test is: check `show ip ospf neighbor` transitions to Full and peer router IDs are unique.

That diagnosis is supported by a different symptom: A two-router point-to-point link unexpectedly elects a DR and follows broadcast-style adjacency rules. Here the recorded observation is: oSPF adjacency fails or behaves inconsistently when duplicate router IDs are present. The applicable cause is: the OSPF domain does not have unique router identifiers for participating routers.

That diagnosis is supported by a different symptom: Hello packets are received but no OSPF neighbor adjacency establishes. Here the recorded observation is: oSPF adjacency fails or behaves inconsistently when duplicate router IDs are present. The applicable cause is: the OSPF domain does not have unique router identifiers for participating routers.

That diagnosis is supported by a different symptom: Two DROthers remain in 2-Way even though the network is forwarding routes normally. Here the recorded observation is: oSPF adjacency fails or behaves inconsistently when duplicate router IDs are present. The applicable cause is: the OSPF domain does not have unique router identifiers for participating routers.

DR and BDR election behavior does not remove a duplicate OSPF router ID between the two neighbors.

That control reduces a separate risk: The peers do not agree on required OSPF hello/dead interval parameters. For the described design, the recurring risk arises from: the OSPF domain does not have unique router identifiers for participating routers. The specific required safeguard is: reserve unique stable router IDs and verify after device replacements.

Changing the OSPF network type does not ensure that each router has a distinct router ID.

Applying the appropriate external redistribution route-map or prefix controls at the ASBR would not make the LAN-facing OSPF interface passive while still advertising its connected prefix as appropriate.

Aligning the OSPF hello and dead timers on the adjacency interfaces would not make the LAN-facing OSPF interface passive while still advertising its connected prefix as appropriate.

Enabling supported OSPFv3 IPv6 routing and adjacencies using IPv6 link-local neighbor reachability would not make the LAN-facing OSPF interface passive while still advertising its connected prefix as appropriate.

This test measures a different behavior: Inspect OSPFv3 neighbors and IPv6 link-local next hops on the interface. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect OSPF interface/passive state and verify no LAN neighbor adjacencies form.

This test measures a different behavior: Compare interface timer fields in OSPF show output and verify neighbors reach Full. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect OSPF interface/passive state and verify no LAN neighbor adjacencies form.

This test measures a different behavior: Inspect redistributed external LSAs and confirm prohibited prefixes are not originated. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect OSPF interface/passive state and verify no LAN neighbor adjacencies form.

That diagnosis is supported by a different symptom: External prefixes still appear in OSPF despite a changed inter-area summary range. Here the recorded observation is: untrusted LAN hosts receive OSPF Hellos and can attempt to form adjacencies. The applicable cause is: the user-facing interface is active for OSPF neighbor discovery instead of passive.

That diagnosis is supported by a different symptom: An operator rejects a valid OSPFv3 design because no global IPv6 address appears on the transit link. Here the recorded observation is: untrusted LAN hosts receive OSPF Hellos and can attempt to form adjacencies. The applicable cause is: the user-facing interface is active for OSPF neighbor discovery instead of passive.

That diagnosis is supported by a different symptom: Hello packets are received but no OSPF neighbor adjacency establishes. Here the recorded observation is: untrusted LAN hosts receive OSPF Hellos and can attempt to form adjacencies. The applicable cause is: the user-facing interface is active for OSPF neighbor discovery instead of passive.

That control reduces a separate risk: The area range controls inter-area summarization, not the ASBR's redistributed external LSA set. For the described design, the recurring risk arises from: the user-facing interface is active for OSPF neighbor discovery instead of passive. The specific required safeguard is: prefer passive-interface default with explicit trusted transit exceptions where supported.

That control reduces a separate risk: OSPFv3 neighbor formation uses link-local addressing on the link, not a required global neighbor address. For the described design, the recurring risk arises from: the user-facing interface is active for OSPF neighbor discovery instead of passive. The specific required safeguard is: prefer passive-interface default with explicit trusted transit exceptions where supported.

That control reduces a separate risk: The peers do not agree on required OSPF hello/dead interval parameters. For the described design, the recurring risk arises from: the user-facing interface is active for OSPF neighbor discovery instead of passive. The specific required safeguard is: prefer passive-interface default with explicit trusted transit exceptions where supported.

Placing ASBR external routes in an area type that supports external LSAs or adjust area design deliberately would not correct the underlying MTU mismatch or carefully use a supported MTU-ignore exception only when justified.

Placing the connected OSPFv3 interfaces into the same intended area, maintaining valid process and instance alignment would not correct the underlying MTU mismatch or carefully use a supported MTU-ignore exception only when justified.

Aligning the OSPF hello and dead timers on the adjacency interfaces would not correct the underlying MTU mismatch or carefully use a supported MTU-ignore exception only when justified.

This test measures a different behavior: Compare interface timer fields in OSPF show output and verify neighbors reach Full. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect adjacency progress and database exchange after matching MTU settings.

This test measures a different behavior: Check OSPFv3 interface area IDs and neighbor state until adjacency reaches Full. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect adjacency progress and database exchange after matching MTU settings.

This test measures a different behavior: Check area type, LSA database and default-route behavior for the selected stub model. It does not establish the target outcome. For the documented fault, the direct acceptance test is: inspect adjacency progress and database exchange after matching MTU settings.

That diagnosis is supported by a different symptom: Hello packets are received but no OSPF neighbor adjacency establishes. Here the recorded observation is: the adjacency never reaches Full despite matching area, hello and dead timers. The applicable cause is: the OSPF database description negotiation detects incompatible interface MTUs.

That diagnosis is supported by a different symptom: External routes are absent inside the stub despite a working internal adjacency. Here the recorded observation is: the adjacency never reaches Full despite matching area, hello and dead timers. The applicable cause is: the OSPF database description negotiation detects incompatible interface MTUs.

That diagnosis is supported by a different symptom: No OSPFv3 adjacency forms despite IPv6 link-local connectivity. Here the recorded observation is: the adjacency never reaches Full despite matching area, hello and dead timers. The applicable cause is: the OSPF database description negotiation detects incompatible interface MTUs.