OSPF Multi Areas on Juniper

OSPF (Open Shortest Path First) is a link-state routing protocol designed to scale efficiently in large networks. At its core, OSPF uses the concept of areas to optimize the distribution of routing information, reduce CPU and memory usage, and provide a modular network design.

What is Area 0?
- Area 0 is also known as the backbone area and is the most critical area in OSPF. Think of it as the spine of a body that connects and supports all other areas.
- All other areas in OSPF must connect to Area 0 through an Area Border Router (ABR). This ensures that routing information flows between all areas effectively.
Why Multiple Areas?
- When all routers are in a single area (like Area 0), they share LSAs (Link-State Advertisements) with each other. This results in:
  - Larger LSDBs (Link-State Databases).
  - Increased CPU and memory usage due to frequent SPF (Shortest Path First) recalculations.
- Multiple areas isolate LSAs and LSDBs, keeping computations local to each area, which improves efficiency.
Benefits of Multiple Areas:
1. Reduced Overhead: Each area processes LSAs and SPF computations independently, minimizing resource consumption.
2. Enhanced Scalability: Networks with hundreds of routers can be broken into smaller, manageable areas.
3. Improved Stability: Changes in one area do not affect the entire network. For example, a link failure in Area 1 will not trigger SPF recalculations in Area 0 or Area 2.