What type of route may not function properly if configured on an Ethernet interface?

A directly attached route refers to routes that are configured for networks that are directly reachable over a network interface, such as Ethernet. When a directly attached route is configured on an Ethernet interface, it relies on that interface being active and functional for proper communication with devices on the same local network.

If the Ethernet interface is down or misconfigured, the directly attached route will not be able to operate correctly because it cannot reach the intended network segment. Therefore, the route would become ineffective, leading to connectivity issues.

In contrast, recursive routes depend on other routes in the routing table to determine their next-hop addresses, which can still function as long as those other routes remain valid. Route re-evaluation pertains to the process by which routing protocols update their routing tables dynamically based on changing network conditions, not specifically tied to the interface in question. A fully specified route provides all necessary parameters to reach a destination but does not inherently rely on the state of the Ethernet interface, making it less susceptible to interface-related issues.

Given this context, the behavior of directly attached routes on an Ethernet interface underscores why this option is the most appropriate answer.