Final answer:
RIPv2 is a purely distance vector routing protocol that uses hop count as its only metric, with a maximum of 15 hops.
Step-by-step explanation:
The correct answer is Option D: RIPv2.
RIPv2, or Routing Information Protocol version 2, is a purely distance vector routing protocol that uses hop count as its only metric. The hop count represents the number of routers a packet must traverse before reaching its destination. In RIPv2, the maximum hop count is 15, meaning that if a route requires more than 15 hops, it is considered unreachable.
For example, if a router A wants to send data to a destination router B, it looks for the route with the lowest hop count in its routing table. If router B is within 15 hops, router A can reach it directly. However, if router B is more than 15 hops away, router A would consider it unreachable.