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 is not so stubby area in OSPF?
In the network diagram, Area 1 is defined as a stub area. IGRP routes cannot be propagated into the OSPF domain because redistribution is not allowed in the stub area. However, if we define Area 1 as NSSA, we can inject IGRP routes into the OSPF NSSA domain with the creation of type 7 LSAs.
How OSPF injects a default route into a not so stubby area?
Introduction. This document shows how Open Shortest Path First (OSPF) injects a default route into a not so stubby area (NSSA). The area border router (ABR) for the NSSA does not, by default, originate a default route into the NSSA. You must use the area nssa default-information originate command.
What is stub and not so 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’s the difference between OSPF stub and NSSA?
Stub area is isolated area that does not receive External LSA. Routers in Stub areas do not receive type 4 and type 5 LSAs it is replaced by a default route to external autonomous system advertised by the area border router (ABR) Stub area can have type 1, 2, and 3 OSPF LSAs.
Is the NSSA ABR generates a default summary route?
By defining an area as a NSSA totally stub area, the NSSA ABR generates a default summary route. As mentioned, if the NSSA area were not defined as totally stub, then a default summary route is not generated by NSSA ABR.
How is NSSA boundary router propagated into OSPF?
An NSSA autonomous system boundary router (ASBR) generates this LSA and an NSSA area border router (ABR) translates it into a type 5 LSA, which gets propagated into the OSPF domain. The network diagram demonstrates this principle. Refer to this network diagram as you use this document: In the network diagram, Area 1 is defined as a stub area.
How does the not so stubby area ( NSSA ) feature work?
Introduction. 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. This document explains how the NSSA feature works.