NSSA

Which of the following OSPF routes are supported by the Not-So-Stubby-Area (NSSA) type? (Select three)

A. O

B. O IA

C. O N2

D. O* N2

E. O* IA

I would go with A, C, D

What do you guys think?

NSSA Blocks Type 4 and 5 LSAs. So the answer should be O, OIA, N2 - A, B, C As OSPF intra Area (O) , OSPF inter area (OIA) and external routes (N2) won't be blocked.

OK. Looks like I need to do some review on that.

But if "O N2" is correct, then "O*N2" should also be correct. The latter is generated by a default-information originate by a member router within the NSSA area.

Robert

I labbed this one up with an AREA 1 NSSA DEFAULT-INFORMATION-ORIGINATE on the ABR bordering areas 0 and 1.

Both LSA 3 and 4 show up as O IA so some of these may be blocked and any type of O E would be blocked as LSA 5 and would not show up in the Area 1 (excluding the ABR).

O, O IA, O N2, O*N2 are all seen in NSSA area 1.

Hmmmmmm... it seems to me that the word "support" is rather ambiguous.

Friends,

In OSPF the nssa blocks only type 5 lsa and instead allows type 7 lsa. But nssa nosummary blocks type 3, type 4 and type 5 and allows type 7 instead.

Hence in nssa the allowed lsa are type 1 type 2 type 3 type 4 and type 7

therefore the answer to the above question should be,

a, b, c

A. because its type 1 and type 2 lsa

b because, type 3 and type 4 lsa are allowed

c because, type 7 is used instead of type 5

d and e are incorrect because * indicates a default candidate but since its a nssa area not nssa nosummary there will be no default candidate as type 1 to 4 are allowed and type 5 is replaced by type 7.

regards, niitin

Yes, I mis-spoke about LSA 4, they are indeed allowed under NSSA. A,B,C is likely the expected answer. However, O*N2 doesn't require NO-SUMMARY and is thus supported under NSSA. Since LSA 4s are not blocked, O*N2 would probably not considered in the top 3 answers.

Robert