What is a stubby area?

An area is referred to as a stub area when there is commonly a single exit point from that area, or if external routing to outside of the area does not have to take an optimal path. A stub is just what it sounds like: a dead end within the network.

What are LSA types?

OSPF LSA Types Explained

• LSA Type 1: Router LSA.
• LSA Type 2: Network LSA.
• LSA Type 3: Summary LSA.
• LSA Type 4: Summary ASBR LSA.
• LSA Type 5: Autonomous system external LSA.
• LSA Type 6: Multicast OSPF LSA.
• LSA Type 7: Not-so-stubby area LSA.
• LSA Type 8: External attribute LSA for BGP.

In which type of area LSA type 4 is not allowed?

Totally Stubby Areas However, neither type can contain an ASBR, as type 4 and 5 LSAs are not permitted inside the area.

What do you mean OSPF areas?

By definition an OSPF area is a collection of networks, not a collection of routers. A backbone network segment is an IP subnet that belongs to the area identified by 0.0. 0.0. Areas that are not physically connected to the backbone are logically connected by a backbone ABR using an OSPF virtual link.

What is not-so-stubby area?

The OSPFv2 not-so-stubby area (NSSA) enables you to configure OSPFv2 areas that provide the benefits of stub areas, but that also are capable of importing external route information. The ASBR inside the NSSA imports external routes from BGP into the NSSA as type 7 LSAs, which the ASBR floods throughout the NSSA.

Why do we use AREA 0 in OSPF?

Albeit OSPF is a link state protocol, the way OSPF handles inter-area traffic leaves it prone to routing loops. This is why OSPF must connect back to area 0 – to avoid routing loops.

Why We Need Not-so-stubby area in OSPF?

Not-so-stubby areas (NSSAs) are an extension of OSPF stub areas. Like stub areas, they prevent the flooding of AS-external link-state advertisements (LSAs) into NSSAs and instead rely on default routing to external destinations.

What are the different types of OSPF areas?

Standard areas can contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area. Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes. Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA.

How does OSPFv3 ABR Type 3 LSA filtering work?

The OSPFv3 ABR Type 3 LSA Filtering feature extends the ability of an ABR that is running the OSPFv3 protocol to filter type 3 LSAs that are sent between different OSPFv3 areas.

How is an OSPF network divided into sub-domains?

An OSPF network can be divided into sub-domains called areas. A router within an area must maintain a topological database for the area to which it belongs. Since the router will not have detailed topology information of routers in other areas, this would greatly reduce the size of database. Areas limit the scope of route information distribution.

What kind of link state advertisements are used in OSPF?

Each area is connected to a central backbone, area zero. OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors. A brief review of the most applicable LSA types: LSA types 1 and 2 are found in all areas, and are never flooded outside of an area.