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Routing & Switching · Advanced

Not-So-Stubby Area (NSSA)

An OSPF stub-like area that blocks Type 5 LSAs but allows a local ASBR to inject externals as Type 7 LSAs.

Definition

NSSAs suit remote sites that must redistribute local routes (for example, a partner connection) while otherwise behaving like a stub. The ABR translates Type 7 to Type 5. Unlike a stub area, an NSSA ABR does not inject a default route automatically unless default-information-originate is configured; totally NSSA (no-summary) does inject one.

Example

area 5 nssa default-information-originate

Exam tip

Totally NSSA = area X nssa no-summary on the ABR; it blocks Type 3 too and auto-generates a default.

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