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 E1 versus E2 external metric. Begin with: Compare external route type, advertised metric, internal ASBR reachability cost and route selection.

Compare OSPF router IDs, neighbor tables and LSA advertising-router fields. This check would diagnose OSPF duplicate router IDs, but would not first isolate the described OSPF E1 versus E2 external metric. Begin with: Compare external route type, advertised metric, internal ASBR reachability cost and route selection.

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 E1 versus E2 external metric. Begin with: Compare external route type, advertised metric, internal ASBR reachability cost and route selection.

Configure reviewed external route import on the intended ASBR and confirm Type 5 LSA propagation into eligible areas. This is a legitimate response to the different issue of OSPF type-5 external advertisement, but it does not correct the specific OSPF stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

Examine LSP sequence numbers and lifetime behavior and correct the root flooding or instability problem. This is a legitimate response to the different issue of IS-IS LSP sequence and aging, but it does not correct the specific OSPF stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

Bind the correct MQC classifier, behavior, and traffic-policy in the intended interface direction. This is a legitimate response to the different issue of MQC classifier and behavior association, but it does not correct the specific OSPF stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

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 stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

An authorized user authenticates into the correct role and invalid identities are rejected. That observation would support a separate case of WLAN 802.1X authentication and NAC, not verification of the reported OSPF stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

A supported Level-1 adjacency forms only between appropriate same-area neighbors and routes appear correctly. That observation would support a separate case of IS-IS level-1 area adjacency, not verification of the reported OSPF stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

OSPF broadcast networks use a designated router to reduce adjacency and LSA exchange overhead. This explains Broadcast OSPF DR and BDR election, but not why the issue in this scenario occurs. The specific mechanism is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

OSPF E1 metrics include internal path cost to the ASBR whereas E2 commonly prioritizes the external metric. This explains OSPF E1 versus E2 external metric, but not why the issue in this scenario occurs. The specific mechanism is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

BGP exchanges routing control messages over an established TCP transport connection. This explains BGP TCP reachability and port, but not why the issue in this scenario occurs. The specific mechanism is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

A Full adjacency is not proof that external prefixes have been injected into OSPF. This consequence is associated more directly with OSPF type-5 external advertisement. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions. This consequence is associated more directly with OSPF LSDB synchronization failure. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

Overbroad aggregation can hide loss of component reachability and blackhole traffic. This consequence is associated more directly with BGP prefix aggregation and specifics. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

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 stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.

Compare OSPF router IDs, neighbor tables and LSA advertising-router fields. This check would diagnose OSPF duplicate router IDs, but would not first isolate the described OSPF stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.

Compare interface MTU, DD packet MTU fields, and OSPF neighbor transition logs. This check would diagnose OSPF MTU stalls ExStart, but would not first isolate the described OSPF stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.

Align OSPF Hello and Dead intervals on both ends with the approved link policy. This is a legitimate response to the different issue of OSPF hello and dead timer mismatch, but it does not correct the specific OSPF stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

Configure supported RR-client relationships and confirm intended reflection rules between client and nonclient sessions. This is a legitimate response to the different issue of BGP route-reflector client scoping, but it does not correct the specific OSPF stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

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 stub area external LSA constraint condition reported. The relevant technical distinction is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

The receiver joins exactly the authorized source and the distribution tree needs no RP for SSM. That observation would support a separate case of Multicast SSM and RPF source path, not verification of the reported OSPF stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

Both peers report synchronized link-state contents and calculate the same viable topology. That observation would support a separate case of IS-IS CSNP and PSNP database sync, not verification of the reported OSPF stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

Neighbor state progresses to Full where adjacency is required and timers remain consistent under observation. That observation would support a separate case of OSPF hello and dead timer mismatch, not verification of the reported OSPF stub area external LSA constraint. The relevant observable outcome here is: Branch routers use the correct default/inter-area reachability without forbidden Type 5 LSAs inside the stub.

Level-1 IS-IS routers commonly use the attached-bit indication to select an inter-area exit. This explains IS-IS L1 default to nearest attached L1L2, but not why the issue in this scenario occurs. The specific mechanism is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

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 stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

Selective IS-IS route leaking can import chosen Level-2 reachability into a Level-1 area. This explains IS-IS selective L2-to-L1 route leaking, but not why the issue in this scenario occurs. The specific mechanism is: OSPF stub areas exclude Type 5 external LSAs and rely on an ABR-generated default for external destinations.

Isolated Level-1 areas cannot reach unrelated areas without a working Level-2 path. This consequence is associated more directly with IS-IS level-2 backbone continuity. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

Changing MTU or route preference cannot repair an area mismatch and can delay recovery. This consequence is associated more directly with OSPF area-ID mismatch. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

Incorrect DIS assumptions can cause inconsistent troubleshooting and churn in shared-segment LSPs. This consequence is associated more directly with IS-IS DIS and pseudonode on broadcast LAN. For the stated conditions the immediate exposure is: Forcing external redistribution into a stub without redesigning its type creates unsupported expectations.

Inspect OSPF interface network type, DR/BDR identity, priority and per-peer state. This check would diagnose Broadcast OSPF DR and BDR election, but would not first isolate the described OSPF stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.

Compare OSPF router IDs, neighbor tables and LSA advertising-router fields. This check would diagnose OSPF duplicate router IDs, but would not first isolate the described OSPF stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.

Inspect AFI/SAFI negotiation, peer AF activation and received EVPN routes. This check would diagnose MP-BGP address-family activation, but would not first isolate the described OSPF stub area external LSA constraint. Begin with: Check area stub configuration on all routers, Type 3 default and any local ASBR attempts.