Exam 300-420 topic 1 question 316 discussion

D is correct IS-IS uses a hierarchical structure with Level 1 and Level 2 areas. Level 1 (L1): Intra-area routing, where routers within a specific area learn about each other. Level 2 (L2): Inter-area routing, where routers connect different areas and form the backbone. Level 1-2 (L1L2): Routers that participate in both Level 1 and Level 2 routing, acting as a bridge between areas and the backbone.

Explanation: Area 49.000 L1: The backbone area should be Level 1 (L1) to allow optimal routing within the area, and to prevent suboptimal routing between routers A1 and A2, they should be in Level 1 within the backbone area. Area 49.001 L1: This area can also be Level 1 (L1) to maintain the same type of routing for the local area. Area 49.002 L2 and area 49.003 L2: Level 2 (L2) areas allow for route-leaking (the ability to share routes between different areas) and summarization. This is a critical requirement for areas 49.002 and 49.003, allowing more flexibility for the network design.