Different Areas of OSPF

What are the OSPF Area Types?

OSPF uses an hierarchical architecture and build OSPF network with different Areas. There are many specific Area types that are used with OSPF and these Area types has specific characteristics. So, what are these areas? General OSPF Area types are:

• Standard Area
• Backbone Area (Area 0)
• Stub Area
• Totally Stubby Area
• NSSA
• Totally NSSA

We will see all these OSPF Area types detailly. Before and during this detailed check, you can use the below diagram to remember OSPF Area types and their specific Advertisement acceptance rules. As you can see below, different OSPF LSA Types are used by different areas.

Let’s check these OSPF Areas one by one.

Standart Area

This Area is the normal Area of OSPF. All Standard Areas must connect to the Area 0. A Standard Area has no specific characteristics. It accepts, LSA Type 1, Type 2, Type 3, Type 4 and Type 5 LSAs.

Backbone Area (Area 0)

Backbone Area (Area 0) is the central of OSPF Network and all the other Areas are connected to thsese Backbone Area. It is similar to Standard Area but it is build as Area 0.

Stub Area

Stub Area is the first specific Area. They are generally used to reduce LSA flooding, the LSDB and routing table size. So, this type of Area is used for the places that is a little sensitive to high traffic.

To configure an Area as “Stub“, all routers in these Area must be configured as “Stub“.

Stub Area accepts Intra Area LSAs, Type 1,Type 2 LSAs. It also accepts, summary routes(Type 3, Type 4) and external routes (Type 5) advertised only by a Default Route. Stub area does not accept external routes(Type 5), it is replaced by Default Route.

Totally Stubby Area

Totally Stubby Area is one step more strict Area than Stub Area. This is a Cisco Proprietary OSPF Area.

To configure an Area as “Totally Stubby“, ABR on this area is configure as Totally Subby Area and the other internal routers is configured as Stub Area.

Totally Stubby Area accepts Intra Area LSAs, Type 1,Type 2 LSAs. It does not accept all inter-area (Type 3, Type 4) and External routes (Type 5). All these routes replaced with Default Route.

Not So Stubby Area (NSSA)

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