Network & Infrastructure / OSPF & Underlay Convergence
Stub and NSSA option mismatches during OSPF adjacency formation
A newly configured area cannot form adjacency after an attempt to reduce external routing information. One endpoint may still expect normal-area capabilities while the other expects stub or NSSA behavior.
Environment and inputs: OSPFv2 IPv4 underlays, with OSPFv3 explicitly identified where used; timers and diagnostics vary by platform. Diagnostic/design example; not tested on production equipment.
Collect the evidence
Compare area type, options advertised in hellos, external-route requirements and all routers sharing the area. Include existing ABRs and any redistribution source in the inventory.
Explain the result
Area capabilities must agree for intended neighbors. Stub and NSSA designs also change which external advertisements can enter or originate; matching a label on one interface is insufficient.
Plan the fix
Choose the area type from actual redistribution and default-routing requirements, then coordinate all participating devices. Do not change an area globally to fix one unverified neighbor.
Check the result and rollback
Verify adjacency, default routes and required external destinations from internal routers. Restore the previous area design if an application loses an external dependency or unintended advertisements appear.