Welcome to a comprehensive exploration of OSPF area types. In this article, we will delve into the five purported OSPF area types and shed light on their true nature. By the end, you will gain a deep understanding of these area types, the LSAs they contain, and the optimizations they offer.
Contents
Understanding OSPF Area Types
To fully grasp OSPF area types, it is crucial to have a solid understanding of OSPF LSAs, specifically types 1, 2, 3, 4, and 5. If you need a refresher on LSAs, please check out the relevant content in “Lesson 9” of our OSPF series.
In our discussion of OSPF area types, we will use a specific topology comprising four areas: Area 0, connected to areas 22, 33, and 44. Each of these areas contains 10 IP subnets, shared via type 1 and type 2 LSAs. Additionally, the Area Border Routers (ABRs) will summarize the information from each area to the other areas in the topology.
The Five OSPF Area Types
While it is commonly believed that there are five OSPF area types, a closer look reveals that there are actually only three core area types. Let’s dive into each of them:
1. Normal Area
The default area type in OSPF is the normal area. In a normal area, all types of LSAs are allowed. This means that type 1, 2, 3, 4, and 5 LSAs can coexist within normal areas.
2. Stub Area
A stub area is a significant optimization of a normal area. In a stub area, type 4 and type 5 LSAs are not allowed. Instead, a stub area injects a default route via a type 3 LSA, providing connectivity to the foreign redistributed subnets. This greatly reduces the number of LSAs that need to be maintained within the area.
3. Not So Stubby Area (NSSA)
A not so stubby area (NSSA) is another form of optimization within OSPF. Similar to a stub area, an NSSA does not allow type 4 and type 5 LSAs. However, an NSSA permits redistribution using a new type of LSA called a type 7 LSA. Type 7 LSAs work similarly to type 5 LSAs, containing the redistributed subnets from the local segment. The ABR within the NSSA translates type 7 LSAs into regular type 5 LSAs, ensuring connectivity to foreign redistributed subnets.
Further Optimizations: Totally Stub and Totally NSSA Areas
While not core OSPF area types, there are additional optimization options available: totally stub and totally NSSA areas.
Totally Stub Area
A totally stub area takes the optimization of a stub area even further. In a totally stub area, type 3 LSAs are not allowed. Instead, a default route is injected via a type 3 LSA. This greatly simplifies the LSAs within the area, reducing the maintenance burden.
Totally Not So Stubby Area (Totally NSSA)
A totally not so stubby area (totally NSSA) is an optimized version of an NSSA. In a totally NSSA, type 3 LSAs are not allowed. Similar to a totally stub area, a default route is injected via a type 3 LSA. This ensures connectivity while significantly reducing the LSAs within the area.
Configuring Area Types
In our next article, we will walk you through the configuration of the different OSPF area types. We will explore the options required to enable totally stub and totally NSSA areas, along with a few additional options. By the end, you will have a clear understanding of how to optimize OSPF area types.
Conclusion
In this article, we have covered the OSPF area types and their optimizations. Understanding OSPF area types allows for efficient management of LSAs and routing within your OSPF network. Stay tuned for our next article in which we will delve into the configuration details of each area type. For more insightful articles on networking and technology, visit Techal.
FAQs
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What are the core OSPF area types?
The core OSPF area types are normal areas, stub areas, and not so stubby areas (NSSAs). -
What is the difference between a stub area and a totally stub area?
A stub area disallows type 4 and type 5 LSAs and injects a default route via a type 3 LSA. In contrast, a totally stub area eliminates type 3 LSAs as well, further simplifying LSAs. -
What is a not so stubby area (NSSA)?
An NSSA disallows type 4 and type 5 LSAs but allows for redistribution using type 7 LSAs. Type 7 LSAs are translated into type 5 LSAs by the ABR. -
What are totally stub and totally NSSA areas?
Totally stub and totally NSSA areas are advanced optimizations that disallow type 3 LSAs while injecting a default route via a type 3 LSA. -
How can I configure OSPF area types?
In our next article, we will walk you through the configuration of each OSPF area type, including the options to enable totally stub and totally NSSA areas. -
Where can I find more informative articles?
For more insightful articles on networking and technology, visit Techal.
