Which OSPF area type can contain Type 7 LSAs?

The not-so-stubby area (NSSA) type in OSPF can contain Type 7 LSAs. NSSAs are designed to allow areas with limited external routing information to receive external routes while still preserving some characteristics of a stub area. Unlike standard stub areas, which block all Type 5 LSAs (external route advertisements), NSSAs can import and translate these Type 5 LSAs into Type 7 LSAs. This flexibility allows NSSAs to redistribute external routes while maintaining the advantages of a stub area, such as reduced routing table size and improved performance.

Type 7 LSAs are specific to NSSAs and are used to transport external route information from within the NSSA to the backbone area. When these Type 7 LSAs are injected into a backbone area, they can be converted to Type 5 LSAs, allowing the information to be propagated to other OSPF areas.

Other area types, such as the backbone area, stub area, and totally stubby area, do not support Type 7 LSAs because they either prevent external routes entirely or do not need the specific functionality that allows for the use of Type 7 LSAs.