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Uyota,
A stub area does not allow external routes. Bt allows Inter-area routes. (Area 1 stub) It should be noted that the backbone area cannot be configured as a stub area. In Other words a stub area does not allow AS External LSA (type 5) into it.
A totally stubby area denies external routes, and Inter area. (Area 1 stub no-summary).
A NSSA just like a stub prevents AS External LSA’s from flooding an area. But in situations where an ASBR is located in an area. The area becomes ineligible to become either a stub or a totally stubby area. The area could be configured as an NSSA. The ABR of that area will be responsible for type 7 LSA translation to type 5 as Routes (External) enter from the NSSA area into the backbone. (area 1 nssa)
A NSSA totally stubby area (area 1 nssa no-summary) does the NSSA type of wat a totally stubby Area does. It does not Allow External LSA’s and also inter-area routes.
To answer your question you configure stub wen u have no ASBR is present in an area and NSSA to do exactly wat a stub does wen an ASBR is present. (A NSSA does nt accept External type 5 bt sends as Type 7 )
Kabir K IbrahimB.sc CCNA CCNP CCDP CCNP MCP +2348036477283
> Date: Tue, 13 May 2008 01:19:20 -0400> From: spycharlies@gmail.com> To: ccielab@groupstudy.com> Subject: ospf stub & NSSA> > Hi guys,> > > > I am not 100% comfortable distinguishing btw. when to use nssa or stub> > > > Assuming R1 connection to the rest of the ospf domain is through R3. Since> R1 does not need specific routing information to the rest of the network, it> just needs to receive only a default route.> > > > ***> > These two solutions seems to be doing the same thing for me> > ***> > *Solution 1*> > > > R3#> > router ospf 1> > area 5 nssa no-summary> > > > R1#> > area 5 nssa.> > > > > > *Sol.2*> > > > R3#> > area 5 stub no-summary> > > > R1#> > area 5 stub> > > > ***> > My question is when can you categorically use nssa over stub, or vice-versa?> > > > Thanks> > > > Uyota> > >