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.

What is stubby area?

A stub area is an area in which you do not allow advertisements of external routes, which thus reduces the size of the database even more. 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 types of LSAs are present in a not-so-stubby area?

Not-so-stubby Areas An NSSA makes use of type 7 LSAs, which are essentially type 5 LSAs in disguise. This allows an ASBR to advertise external links to an ABR, which converts the type 7 LSAs into type 5 before flooding them to the rest of the OSPF domain. Type 3 LSAs will pass into and out of the area.

What is totally not-so-stubby area in OSPF?

The OSPF not-so-stubby area (NSSA) feature is described by RFC 1587. and is first introduced in Cisco IOS® Software release 11.2. It is a non-proprietary extension of the existing stub area feature that allows the injection of external routes in a limited fashion into the stub area.

What is NSSA stubby totally stubby?

Basically NSSA and NSSA totally stubby are comparable to stub area and totally stubby area, respectively, with the exception of external route redistribution capabilities. NSSA will allow all Type 3 LSAs, while a totally stubby NSSA will have only one Type 3 LSA, i.e. the default route.

How do you set up a stubby area?

To configure OSPF stub areas:

  1. On all routing devices in the area, configure an OSPF stub area.
  2. On the ABR, inject a default route into the area.
  3. (Optional) On the ABR, restrict summary LSAs from entering the area.
  4. If you are done configuring the devices, commit the configuration.

What is Area 0 called in OSPF?

backbone area
The backbone area (Area 0) is the core of an OSPF network. All other areas are connected to it and all traffic between areas must traverse it. All routing between areas is distributed through the backbone area.

What is the difference between stub and totally stubby area?

A stub area is an area in which advertisements of external routes are not allowed, reducing the size of the database. A totally stubby area (TSA) is a stub area in which summary link-state advertisement (type 3 LSAs) are not sent.

What is a Type 3 LSA?

Area 0 doesn’t need to know how the routers in Area 1 are connected. So the Type-3 LSA summarizes this information by only reporting what networks exist in the area. Same thing for Area 0. There are Type-1 and Type-2 LSAs that describe the topology of Area 0 in detail.

What is totally NSSA?

totally NSSA – filter even more prefixes/LSAs entering the area, but allow external routes being generated from this specific area.

What is the difference between stub area and NSSA?

An OSPF stub area has no external routes in it, so you cannot redistribute from another protocol into a stub area. A not-so-stubby area (NSSA) allows external routes to be flooded within the area. These routes are then leaked into other areas. However, external routes from other areas still do not enter 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.

What does not-so-stubby-area mean in OSPF?

Not-so-stubby-area, is a stub area which needs to distribute external routes into OSPF, however if a stub area is unable to distribute external route into a stub area because type 4 and 5 LSAs are filtered, hence for a stub area to be able to redistribute external route and still maintain a stubby area status Not-so-stubby-area is configured.

What’s the difference between stub areas and totally stubby areas?

By designating area 0.0.0.3 as a stub area, you reduce the size of the topology database for that area by limiting the route entries to only those routes internal to the area. A stub area that only allows routes internal to the area and restricts Type 3 LSAs from entering the stub area is often called a totally stubby area.

How does not so stubby area ( NSSA ) work?

Not-So-Stubby Area (NSSA) behaves like Stub area. It allows Inter-Area (O IA), Intra-Area, and default routes. LSA Type 1, Type 2, Type 3are allowed but unlike Stub area, External LSAs are allowed in NSSA area.

How to make area 0.0.3 a totally stubby area?

You can convert area 0.0.0.3 to a totally stubby area by configuring the ABR to only advertise and allow the default route to enter into the area. External routes and destinations to other areas are no longer summarized or allowed into a totally stubby area.

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