What protocol uses a hop count as its primary metric?

The correct answer is based on the fact that RIP (Routing Information Protocol) primarily uses hop count as its metric for path selection. In RIP, each hop between routers is given a value of one, and the maximum number of hops allowed in a RIP network is 15, with 16 hops indicating an unreachable network. This simple metric helps in determining the shortest path to a destination by counting the number of routers in the path.

RIP's design is centered around simplicity and ease of use, making it suitable for smaller networks. Its reliance on just hop count means that it does not consider other factors such as bandwidth or delay, which can lead to suboptimal routing decisions in more complex network scenarios.

In contrast, protocols like OSPF (Open Shortest Path First) and EIGRP (Enhanced Interior Gateway Routing Protocol) use different metrics such as cost and composite metrics (which can include bandwidth and delay), respectively, thus providing more nuanced routing decisions based on the overall quality of the path, rather than just the number of hops. IS-IS (Intermediate System to Intermediate System) also uses a different method focusing on link metrics rather than just hop count.