Refer to the exhibit.

The correct IS-IS hierarchy places area 49.000 as Level 2 and areas 49.001, 49.002, and 49.003 as Level 1. In IS-IS, Level 2 forms the interarea backbone, while Level 1 areas contain local topology details. This design supports growth in the backbone because Level 2 routers exchange interarea reachability without carrying every local topology change from every access area. Areas 49.002 and 49.003 can perform summarization and route leaking at their Level 1/Level 2 boundaries, allowing routers such as A1 and A2 to avoid suboptimal routing by learning selected more-specific routes from the backbone when necessary. If the nonbackbone areas were made Level 2, the design would flatten the hierarchy and expose more of the network to topology changes. If the backbone were Level 1, interarea routing would be broken or badly constrained. The selected hierarchy preserves scaling, allows route control, and avoids unnecessary propagation of local link flaps. Reference topics: IS-IS hierarchy, Level 1 areas, Level 2 backbone, route leaking, summarization, scaling.