Refer to the exhibit. An engineer is designing a hierarchical ISIS solution for an enterprise customer with these requirements: - Users in areas 25 and 55 send and receive traffic from both backbone…

This configuration would place Level 2 routers in areas meant for isolation (35, 45) and Level 1 routers (C series) in what should be a backbone area (55), preventing proper inter-area routing and isolation.

An all Level 1/2 design would propagate link flaps more broadly, failing to meet the requirement for isolating instability in areas 35 and 45 by not creating distinct Level 1 boundaries.

Configuring B and C series as Level 2 means areas 35 and 45 would be part of the Level 2 backbone, which would not isolate link flaps and growth from other areas as required.

Configuring A series routers as Level 1 creates Level 1 areas (like 25), B series as Level 1/2 enables them to connect Level 1 areas (35, 45) to the Level 2 backbone and isolate link flaps, and C series as Level 2 forms the reliable backbone (55) to carry inter-area traffic.