Which two link-state advertisement (LSA) types are allowed in a stub area?

In OSPF (Open Shortest Path First) routing, stub areas are a specific type of area designed to reduce the number of external routes that routers within the area must process and advertise. By limiting the types of Link-State Advertisements (LSAs) that can be generated and exchanged within a stub area, OSPF optimizes performance and resource utilization.

The LSA types that are permitted in a stub area include Type 1 and Type 2. Type 1 LSAs, also known as Router LSAs, are generated by each router within the OSPF area and contain information about the router's interfaces, their states, and the cost to reach each interface. This information is vital for local route calculation within the area.

Type 2 LSAs are known as Network LSAs, which are generated by the designated router for multi-access networks. They describe the routers connected to the same network segment and their relationships, which is essential for building the OSPF topology for that segment.

On the other hand, Type 4 and Type 5 LSAs, which are used to propagate information about summary routes and external routes respectively, are not allowed in a stub area. This is a key characteristic of stub areas, as they are