To automatically build a routing table, which type of indirect routing must a router implement?

Dynamic routing is the correct choice for automatically building a routing table because it allows routers to exchange information about reachable networks automatically. Through the use of routing protocols such as RIP, OSPF, or EIGRP, routers can learn about network changes and updates in real time. This capability to adapt to changes—whether due to new networks being added, existing networks being removed, or downed paths—ensures that routing tables are always current without the need for manual intervention.

In contrast, static routing involves manually configuring routes, which does not accommodate changes in the network environment dynamically. Default routing serves a specific purpose, allowing packets that do not match other routes to be sent to a particular next-hop router but does not automatically build a comprehensive routing table. Manual routing, while similar to static routing, implies even more direct human intervention and lacks the adaptive capabilities inherent to dynamic routing methods. Thus, dynamic routing stands out as the method that builds and updates routing tables automatically and efficiently.