Inspect pool membership, client VLAN assignment, DHCP lease utilization and authentication policy. This check would diagnose WLAN VLAN pool address distribution, but would not first isolate the described OSPF MTU stalls ExStart. Begin with: Compare interface MTU, DD packet MTU fields, and OSPF neighbor transition logs.

Compare OSPF authentication settings and discarded authentication-failure counters. This check would diagnose OSPF authentication-key mismatch, but would not first isolate the described OSPF MTU stalls ExStart. Begin with: Compare interface MTU, DD packet MTU fields, and OSPF neighbor transition logs.

Inspect import policy, level-specific LSP advertisements and the Level-1 route table. This check would diagnose IS-IS selective L2-to-L1 route leaking, but would not first isolate the described OSPF MTU stalls ExStart. Begin with: Compare interface MTU, DD packet MTU fields, and OSPF neighbor transition logs.

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 LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

Check supported PIM-SM shortest-path-tree switchover thresholds and source-side unicast reachability. This is a legitimate response to the different issue of PIM-SM RPT to SPT switchover, but it does not correct the specific OSPF LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

Review the ABR Type 3 summary LSA policy and advertise the intended inter-area prefix. This is a legitimate response to the different issue of OSPF type-3 inter-area summaries, but it does not correct the specific OSPF LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

The partner prefix appears as an external route where allowed and test traffic reaches its next hop. That observation would support a separate case of OSPF type-5 external advertisement, not verification of the reported OSPF LSDB synchronization failure. The relevant observable outcome here is: Both routers report Full and their relevant area LSDBs are synchronized.

A stack-link fault produces the designed protective isolation with one coherent active forwarding system. That observation would support a separate case of Switch stacking split-brain, not verification of the reported OSPF LSDB synchronization failure. The relevant observable outcome here is: Both routers report Full and their relevant area LSDBs are synchronized.

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 LSDB synchronization failure. The relevant observable outcome here is: Both routers report Full and their relevant area LSDBs are synchronized.

IS-IS uses Level-2 routing for inter-area exchange between Level-1 domains. This explains IS-IS level-2 backbone continuity, but not why the issue in this scenario occurs. The specific mechanism is: OSPF requires successful database description, request and update exchange to complete adjacency.

Inter-area OSPF route summarization occurs at ABRs when advertising reachability between areas. This explains OSPF inter-area summarization placement, but not why the issue in this scenario occurs. The specific mechanism is: OSPF requires successful database description, request and update exchange to complete adjacency.

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 requires successful database description, request and update exchange to complete adjacency.

Removing all protocol authentication to restore routing exposes adjacencies to spoofed updates. This consequence is associated more directly with OSPF authentication-key mismatch. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

Ignoring community-scoped policy can expose unintended network reachability. This consequence is associated more directly with BGP community filtering in routing control. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

Treating intentional Type 3 suppression as a link failure prompts unnecessary OSPF resets. This consequence is associated more directly with OSPF totally stub area inter-area constraint. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

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 LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.

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 LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.

Audit security policy order, matching zones and addresses, and permitted-versus-denied test flows. This check would diagnose Default-deny network segmentation, but would not first isolate the described OSPF LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.

Place both ends of the adjacency in the intended common OSPF area and verify area design constraints. This is a legitimate response to the different issue of OSPF area-ID mismatch, but it does not correct the specific OSPF LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

Adopt a scalable hierarchical campus design with sensible access, distribution, core and segmentation boundaries. This is a legitimate response to the different issue of Enterprise campus layered design, but it does not correct the specific OSPF LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

Verify DR/BDR election and accept 2-Way between appropriate DROther peers instead of forcing unnecessary full meshes. This is a legitimate response to the different issue of Broadcast OSPF DR and BDR election, but it does not correct the specific OSPF LSDB synchronization failure condition reported. The relevant technical distinction is: OSPF requires successful database description, request and update exchange to complete adjacency.

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 LSDB synchronization failure. The relevant observable outcome here is: Both routers report Full and their relevant area LSDBs are synchronized.

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

The route and forwarding entries agree and a packet trace takes the selected viable next hop. That observation would support a separate case of RIB-to-FIB forwarding discrepancy, not verification of the reported OSPF LSDB synchronization failure. The relevant observable outcome here is: Both routers report Full and their relevant area LSDBs are synchronized.

IS-IS identifies the freshness of LSPs using sequence numbers and lifetime fields. This explains IS-IS LSP sequence and aging, but not why the issue in this scenario occurs. The specific mechanism is: OSPF requires successful database description, request and update exchange to complete adjacency.

OSPF ABRs convey eligible inter-area reachability through network summary LSAs. This explains OSPF type-3 inter-area summaries, but not why the issue in this scenario occurs. The specific mechanism is: OSPF requires successful database description, request and update exchange to complete adjacency.

VRRP presents a shared virtual IP/MAC gateway that a current master forwards on behalf of the group. This explains VRRP virtual gateway and ownership, but not why the issue in this scenario occurs. The specific mechanism is: OSPF requires successful database description, request and update exchange to complete adjacency.

Absent or misleading attached exits can strand a local area or direct it into an invalid path. This consequence is associated more directly with IS-IS L1 default to nearest attached L1L2. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

Changing static-route priority will not fix unintended OSPF intra-area path cost. This consequence is associated more directly with OSPF SPF path-cost comparison. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

Duplicate router IDs can corrupt topology interpretation and interrupt route convergence. This consequence is associated more directly with OSPF duplicate router IDs. For the stated conditions the immediate exposure is: Assuming a Hello neighbor alone provides a complete topology can create inconsistent routing decisions.

Inspect Level-2 LSDBs, adjacency levels, attached bits and inter-area route tables. This check would diagnose IS-IS level-2 backbone continuity, but would not first isolate the described OSPF LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.

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 LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.

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 LSDB synchronization failure. Begin with: Inspect neighbor phase, LSR retransmission lists, relevant LSAs and interface loss.