A retail IS-IS network has Level 1 stores, Level 2 core, excessive leaking causing large store tables, inconsistent metrics after migration, and need for 10 aggregate routes at borders. Stability is the goal. Which IS-IS route leaking, summarization and metric style combination best stabilizes this hierarchy?

The correct combination stabilizes the hierarchy because filtering Level 2 to Level 1 leaking to a default keeps store Level 1 tables minimal while preserving core reachability, summarization at L1/L2 borders replaces many site prefixes with the required 10 aggregates and limits LSP flooding and SPF work, and consistent wide metrics provide large metric space and modern sub-TLV support that resolve post-migration inconsistency. The selective leaking choice fails by route-leaking concept because even a controlled set of Level 2 prefixes reintroduces excess state into Level 1 and defeats the default-only design needed to fix large store tables where stability outweighs optimality. The internal summarization choice fails by aggregation-placement concept because summarizing on Level 1 internal routers hides detail in the wrong place and does not constrain advertisements across the L1/L2 boundary where the aggregates must be created. The narrow-metric choice fails by metric concept because narrow metrics allow only small interface and path costs and lack wide-metric extensions, so retaining them perpetuates inconsistency and limits scalability. As an exam caveat, remember IS-IS naturally advertises Level 1 routes into Level 2 but does not leak Level 2 into Level 1 unless configured, so distinguish attached defaults from explicit leaking. As a practical check, verify wide metrics on all IS-IS interfaces and confirm store tables contain only local Level 1 routes plus defaults while border routers advertise exactly the planned aggregates.