What is the third type of indirect routing, alongside static and dynamic routing?

Default routing is indeed the third type of indirect routing that complements static and dynamic routing. In networking, default routing is used when a router does not have an explicit route to a destination. Instead of needing a complete routing table, the router can send packets to a predefined next-hop address, which serves as the default path for any destination not specifically listed.

This method is particularly useful in simplifying routing decisions and conserving memory because it allows routers to manage fewer routes. It is commonly used in scenarios where a router acts as a gateway to the internet or another large network. Since static routing involves manually configured routes, and dynamic routing utilizes algorithms to find optimal paths based on current network conditions, default routing provides a straightforward fallback option when no specific path is known.

The other choices, such as flexible routing, static path routing, and adaptive routing, do not represent established categories of indirect routing in the same way that default routing does. They may refer to concepts or strategies within routing but are not recognized as the third standard form of indirect routing.