3.6.d LSA types area type backbone, normal, transit, stub, NSSA, totally stub

this document speaks volumes…

from: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a88.shtml

nssa.gif

In the network diagram, Area 1 is defined as a stub area. IGRP routes cannot be propagated into the OSPF domain because redistribution is not allowed in the stub area. However, if we define Area 1 as NSSA, we can inject IGRP routes into the OSPF NSSA domain with the creation of type 7 LSAs. Redistributed RIP routes are not allowed in Area 1 because NSSA is an extension to the stub area. The stub area characteristics still exist, which includes no type 5 LSAs allowed.