A Stub area is where External LSA (type 5) and ASBR Summary LSA (type 4) are not flooded. If we happen to use command no-summary then it will be a totally-stub-area which besides LSA type 5 and type 4, it will not flood Network Summary LSA (type 3).

From the above understanding, we cannot do redistribution within stub area as redistribution will create External LSA (type 5). Again, a stub area is where External LSA (type 5) and ASBR summary LSA (type 4) are not being flooded.

We might all know that we have not-so-stubby-area (NSSA) if we want to use redistribution in stub area. But, allow me to post my experience on how I get this understanding.

I have a stub area. The lab says that:
1. Create a loopback address and redistribute this to OSPF
2. Change the area into NSSA.

Task 1 was damn easy! I rushed to my keyboard and typing madly.

int lo10
 ip addr 10.10.10.10 255.255.255.255
router ospf 1
 redistribute connected subnets

Wouldn’t be that hard, would it? until I saw this.

*Mar  1 02:06:04.183: %OSPF-4-ASBR_WITHOUT_VALID_AREA: Router is currently an 
ASBR while having only one area which is a stub area

Huh, what was that? Googling only gives me this
http://www.cisco.com/en/US/docs/ios/12_2sx/system/messages/sm2sx06.html

Error Message    %OSPF-4-ASBR_WITHOUT_VALID_AREA: Router is currently an ASBR while having only one area which is a stub area
Explanation    An ASBR must be attached to an area which can carry AS external or NSSA LSAs.

Recommended Action    Make the area to which the router is attached into an NSSA or regular area.

I was 100% sure that my routers were not ASBR, I don’t believe that another router / switches leaking its L2 somewhere, and it is a Stub area. It took me about 1 hour just to make sure of this, for several times. I’ve even reloaded the router and switches not knowing where the problem was.

Recommended action advised me to change the router into NSSA or regular area. NO! I don’t want that! I want my stub to be able to redistribute my lo10.

I checked the lab and it says 2. Change the area into NSSA. Then I grabbed my Routing TCP/IP vol1 to check why.

Ok, again, stub area won’t flood LSA Type 5, therefore I could not do my redistribution.

(and No, I cannot use ip ospf 1 are 3 command in my lo10 as the lab clearly says to redistribute).

Changed my area into NSSA fixed the issue. Good lesson learned.