Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements. This check would diagnose OSPF external summarization at ASBR, but would not first isolate the described OSPF inter-area summarization placement. Begin with: Compare address blocks, ABR area-range settings, Type 3 LSAs and specific-prefix reachability.

Compare interface-to-area bindings and Hello area fields on both peers. This check would diagnose OSPF area-ID mismatch, but would not first isolate the described OSPF inter-area summarization placement. Begin with: Compare address blocks, ABR area-range settings, Type 3 LSAs and specific-prefix reachability.

Inspect port roles, proposal/agreement exchanges, physical link state and failover logs. This check would diagnose RSTP alternate port failover, but would not first isolate the described OSPF inter-area summarization placement. Begin with: Compare address blocks, ABR area-range settings, Type 3 LSAs and specific-prefix reachability.

Correct incompatible MTU assumptions and verify the OSPF database description exchange. This is a legitimate response to the different issue of OSPF MTU stalls ExStart, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Tune approved OSPF link costs to represent the intended path preference and re-evaluate SPF. This is a legitimate response to the different issue of OSPF SPF path-cost comparison, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Repair the allowed IS-IS database synchronization exchanges and check CSNP/PSNP and LSP sequence handling. This is a legitimate response to the different issue of IS-IS CSNP and PSNP database sync, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Both routers report Full and their relevant area LSDBs are synchronized. That observation would support a separate case of OSPF LSDB synchronization failure, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

The peer relationship reaches the expected adjacency state and area routing updates arrive. That observation would support a separate case of OSPF area-ID mismatch, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

The leaf follows the intended default path and its LSDB lacks the suppressed detailed inter-area summaries. That observation would support a separate case of OSPF totally stub area inter-area constraint, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

OSPF SPF computes paths from the link-state topology using accumulated interface costs. This explains OSPF SPF path-cost comparison, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

IP forwarding uses longest-prefix match; protocol route preference decides among competing candidates for the same prefix. This explains Longest-prefix and route preference, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

OSPF Hello validation requires compatible area identifiers across a participating link. This explains OSPF area-ID mismatch, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Confusing ABR summary handling with ASBR external import can hide the root cause. This consequence is associated more directly with OSPF type-3 inter-area summaries. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Mismatched neighbor timers can leave a functioning IP link without dynamic routes. This consequence is associated more directly with OSPF hello and dead timer mismatch. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Incorrectly treating an old LSP as current can preserve outdated reachability after recovery. This consequence is associated more directly with IS-IS LSP sequence and aging. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Inspect the ABR LSDB for Type 3 prefixes, area ranges and inter-area filter policy. This check would diagnose OSPF type-3 inter-area summaries, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.

Check area stub configuration on all routers, Type 3 default and any local ASBR attempts. This check would diagnose OSPF stub area external LSA constraint, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.

Inspect the Huawei IP routing table, FIB entries, adjacency resolution and a test flow. This check would diagnose RIB-to-FIB forwarding discrepancy, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.

Verify Type 7 origination in the NSSA and approved translation to Type 5 at an eligible ABR. This is a legitimate response to the different issue of OSPF NSSA type-7 translation, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Repair the allowed IS-IS database synchronization exchanges and check CSNP/PSNP and LSP sequence handling. This is a legitimate response to the different issue of IS-IS CSNP and PSNP database sync, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Apply supported area-range inter-area summarization at the ABR using a safe nonoverlapping aggregate. This is a legitimate response to the different issue of OSPF inter-area summarization placement, but it does not correct the specific OSPF external summarization at ASBR condition reported. The relevant technical distinction is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

OSPF authentication errors cease and the expected peer adjacency returns without disabling authentication. That observation would support a separate case of OSPF authentication-key mismatch, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

The preferred gateway is master under healthy conditions and backup is ready for takeover. That observation would support a separate case of VRRP priority and intended master, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

Downstream areas learn the intended aggregate while required exceptions remain reachable. That observation would support a separate case of OSPF inter-area summarization placement, not verification of the reported OSPF external summarization at ASBR. The relevant observable outcome here is: Eligible areas see the intended external aggregate and services within it retain correct reachability.

IS-IS Level-1 neighbor relationships require compatible area addressing while Level-2 uses broader backbone reachability. This explains IS-IS level-1 area adjacency, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

Source NAT rewrites private source addresses for traffic needing routable external identities. This explains Source NAT for outbound clients, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

OSPF protocol authentication rejects Hellos or updates that do not meet the agreed security parameters. This explains OSPF authentication-key mismatch, but not why the issue in this scenario occurs. The specific mechanism is: OSPF external route summarization is performed on an ASBR, distinct from ABR inter-area summary generation.

A healthy adjacency without a consistent LSDB may produce transient wrong paths. This consequence is associated more directly with IS-IS CSNP and PSNP database sync. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Misunderstanding E2 treatment can produce asymmetric or longer-than-expected external paths. This consequence is associated more directly with OSPF E1 versus E2 external metric. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Mismatched metric styles can hide prefixes or distort shortest-path selection. This consequence is associated more directly with IS-IS metric-style consistency. For the stated conditions the immediate exposure is: Applying the policy at the wrong routing role leaves external LSAs unchanged.

Compare destination address, prefix lengths, active candidate routes and the FIB lookup. This check would diagnose Longest-prefix and route preference, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.

Compare interface cost values, SPF results, route cost and the selected next hop. This check would diagnose OSPF SPF path-cost comparison, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.

Trace Type 7 advertisements, P-bit or translation selection and Type 5 LSAs outside the NSSA. This check would diagnose OSPF NSSA type-7 translation, but would not first isolate the described OSPF external summarization at ASBR. Begin with: Inspect redistributed prefix ownership, ASBR aggregation policy, and emitted Type 5 advertisements.