01Plain English
The simple explanation
An ASBR inside an NSSA can introduce external routes without filling the area with Type 5 LSAs.
02Under the hood
The technical explanation
Type 7 LSAs flood within their NSSA. An elected or configured NSSA translator can translate eligible Type 7 LSAs into Type 5 LSAs for distribution beyond it. Translation depends on protocol conditions and policy; it is not a rule that every Type 7 becomes a Type 5.
Protocol reference: RFC 2328 (OSPFv2). NSSA reference: RFC 3101.
logic
Make it stick
The local correspondent whose story needs approval before the international edition.
03On the wire
Example
A branch NSSA redistributes a local external route. The NSSA carries Type 7 information; a qualifying translated Type 5 advertises it outside.