Why design OSPF hierarchically — benefits of multiple areas What are the main reasons for deploying OSPF in a hierarchical, multi-area design?

Introduction / Context:
As networks grow, link-state protocols can experience large databases and frequent recalculation. OSPF counters this by partitioning the network into areas, with area 0 as the backbone. Understanding the advantages of a hierarchical design is essential for scaling and operational stability.

Given Data / Assumptions:

• We consider standard OSPF multi-area designs (ABRs, area 0).
• Goals typically include performance, stability, and manageability.
• Results can vary by topology, but core benefits are well established.

Concept / Approach:
Hierarchical OSPF localizes flooding and SPF recalculation. When a link changes within an area, only that area’s routers recalculate; ABRs summarize and limit LSAs across area boundaries. This reduces routing overhead, speeds convergence in the wider domain, and confines instability so that a single area’s churn does not impact others.

Step-by-Step Solution:
Partition the network into multiple areas with area 0 as the core.Use ABRs to limit LSA flooding and optionally summarize routes between areas.Observe reduced LSDB sizes per area and faster SPF runs after localized changes.Note that failures are contained within an area, improving domain-wide stability.

Verification / Alternative check:
Compare show ip ospf database sizes and SPF timers in single-area vs. multi-area pilots; multi-area deployments show smaller LSDBs per router and fewer domain-wide recomputations after localized events.

Why Other Options Are Wrong:

• B: Understates benefits; convergence and overhead do improve.
• C/D: Overstate by suggesting universal simplicity; hierarchical design helps but does not guarantee trivial configuration.
• E: Irrelevant; static routing is not a goal of hierarchical OSPF.

Common Pitfalls:
Believing any multi-area split automatically simplifies configuration; poor area design can complicate things. Benefits rely on sensible summarization and stable ABR placement.

Final Answer:
To decrease routing overhead, speed up convergence, and confine instability to single areas