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Question

Which of the following statements is correct about external routes received by an NSSA?

A.	External routes from an ASBR are converted to Type 3 LSAs and tunneled through the NSSA to the ABR, where they are converted to Type 5 LSAs.
B.	External routes from an ASBR are converted to Type 3 LSAs and tunneled through the NSSA to the ABR, where they are converted to Type 7 LSAs.
C.	External routes from an ASBR are converted to Type 5 LSAs and tunneled through the NSSA to the ABR, where they are advertised as Type 5 LSAs.
D.	External routes from an ASBR are converted to Type 5 LSAs and tunneled through the NSSA to the ABR, where they are converted to Type 7 LSAs.
E.	External routes from an ASBR are converted to Type 7 LSAs and tunneled through the NSSA to the ABR, where they are converted to Type 5 LSAs.
F.	External routes from an ASBR are converted to Type 7 LSAs and tunneled through the NSSA to the ABR, where they are advertised as Type 7 LSAs.

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Accepted Answer

External routes from an ASBR are converted to Type 7 LSAs and tunneled through the NSSA to the ABR, where they are converted to Type 5 LSAs.

Accepted Answer

External routes from an autonomous system boundary router (ASBR) are converted to Type7 link-state advertisements (LSAs) and tunneled through the not-so-stubby area (NSSA) to the area border router (ABR), where they are converted to Type 5 LSAs. An NSSA is basically a stub area that contains one or more ASBRs. Type 7 LSAs are used to advertise external routes that are injected into an Open Shortest Path First (OSPF) NSSA.

External routes from an ASBR into an NSSA are not converted to Type 5 LSAs and tunneledthrough the NSSA to the ABR. Type 5 LSAs are used to advertise external routes that are injected into an OSPF backbone or standard area. When an ASBR in a backbone area or a standard area receives an external route, the ASBR creates a Type 5 LSA to advertise the external route. Like stub areas, NSSAs do not accept or create Type 5 LSAs.

External routes from an ASBR into an NSSA are not converted to Type 3 LSAs and tunneled through the NSSA to the ABR. Type 3 LSAs are used to advertise the area's subnets to another area. NSSAs accept Type 3 LSAs. However, Type 3 LSAs are not created by ASBRs; they are created by ABRs. Totally stubby areas and totally NSSAs do not accept Type 3, 4, or 5 summary LSAs. These LSAs are replaced by a default route at the ABR. As a result, routing tables are kept small within the totally stubby area.