Which of the following tools is NOT used for route filtering?

The correct choice reflects an understanding of the specific tools used for route filtering in networking. Policy-based routing, although a routing feature, doesn't inherently serve as a route filtering tool. Instead, it allows the network administrator to define routing decisions based on policies. This means that while it can influence routing behavior, it doesn't specifically filter routes based on criteria like prefixes or communities, which are the primary functions of route filtering tools.

In contrast, IP-prefix and IP community-filter are explicitly designed for filtering purposes. An IP-prefix can match routes based on their prefix length, allowing for the inclusion or exclusion of specific routes based on address blocks. Similarly, IP community-filter leverages BGP communities to manage route propagation and filtering according to predefined community tags.

OSPF, while a routing protocol itself, can be configured to perform certain filtering tasks through route summarization and route advertisement controls. However, its primary function is to enable dynamic routing between devices rather than serve solely as a filtering mechanism.

Thus, understanding that policy-based routing is more about decision-making rather than filtering helps clarify why it's accurately identified as the tool that is not used specifically for route filtering.