OSPF NSSA area

[Sharanjeet_Kumar]

Hello,

I've a query about ospf nssa area, looking for anyone's help

what will happen if we make a regular area (for eg area 1) as a NSSA area ????? 

Thanks!!!!!!!!

[M02@rt37]

Hello @Sharanjeet_Kumar 

Converting a regular OSPF area to an NSSA area limits the propagation of external routes and ASBR-generated default routes, and requires Type-7 LSAs to be translated to Type-5 LSAs for propagation throughout the OSPF domain.

[MHM Cisco World]

this table must you remember always, 
the different between area is the LSA each area accept, 
NSSA not accept LSA4&5 but accept LSA7.

[paul driver]

Hello
All normal ospf areas need to learn about external routes, and to get to those external routes then each router needs learn the ABSR routers that has advertised them, and this is done learning type 4/5 LSAs

When you stub an area then the internal routers within that stub area have no need to learn about any external routes, only the ABR’s of the stub area needs to know, a such those type 4/5 LSA can be filtered, so no external routes will be learned by internal routers within stubby areas, they will still be able to reach any external prefixes by the ABR of the stub area that will advertise a default route into the stub area so all internal routers of the stubby area has a gateway out of  its area.

When you Not So Stub an Area (NSSA) this mean routers within this NSSA can redistribute external routes into this area however as type 5 LSAs are still not permitted then those external routes are advertised with a type 7 LSA

So the difference between a OSPF stub area and NSSA is the ability to advertise external routes within a stub area.