Type 4 LSA and NSSA

Hi,
When the type-7 LSA that describes the external network leaves the NASS area, the ABR of the NSSA area changes the LSA from type 7 to type-5 and advertises the LSA to other common areas.  In this case, the type-5 LSAs are advertised by the ABR. The ABR that changes from type-7 to type-5 is determined as an ASBR by the members of other areas. The members of the backbone area still determine the location of the ASBR through type 1/2 LSAs.
Area 2 does not have type-1 or type-2 LSAs of the backbone area. Therefore, the ABR in area 2 needs to deliver type-4 LSAs to describe the topology information of the ASBR.  
Therefore, R5 and R6 each generate two types of LSAs to describe the locations of R2 and R3.  type-4 LSAs exist only in area 2, and the R7 receives 4  type-4 LSAs.