Introduction:
When it comes to selecting a routing protocol, it is important to consider various factors such as network size, scalability, convergence time, and network diameter. The network diameter refers to the maximum number of hops between two nodes in a network. In this scenario, where the network diameter is more than 17 hops, the most suitable protocol to select would be RIPv2.

Explanation:
RIPv2 (Routing Information Protocol version 2) is an enhanced version of RIPv1 that provides several improvements and features. Let's discuss why RIPv2 is the best choice in this case:

1. Hop count limitation:
RIPv1 uses hop count as the metric to determine the best path for routing. The maximum hop count value in RIPv1 is 15, which means it can only handle networks with a diameter of up to 15 hops. Beyond that, the hop count value wraps around, causing incorrect routing decisions. In contrast, RIPv2 uses a 32-bit metric field, allowing it to handle networks with a diameter larger than 15 hops.

2. Classless routing:
RIPv2 supports classless routing, which means it can handle variable-length subnet masks (VLSM). This is crucial for efficient network utilization, as it allows for more flexible addressing and allocation of IP addresses. RIPv1, on the other hand, only supports classful routing, which can lead to wastage of IP addresses and inefficient network design.

3. Authentication:
RIPv2 provides authentication mechanisms to ensure the integrity and security of routing information. This helps prevent unauthorized access and tampering of routing updates. RIPv1, on the other hand, does not have any built-in authentication mechanisms, making it more vulnerable to security threats.

4. Faster convergence:
RIPv2 has faster convergence compared to RIPv1. Convergence refers to the time it takes for all routers in a network to update their routing tables after a change in network topology. RIPv2 uses triggered updates and split horizon with poison reverse techniques to minimize convergence time. RIPv1, on the other hand, relies on periodic updates, which can lead to slower convergence.

Conclusion:
Considering the network diameter of more than 17 hops, RIPv2 is the most appropriate choice due to its ability to handle larger networks, support for classless routing, authentication mechanisms, and faster convergence. It provides the necessary features and scalability required for efficient routing in larger networks compared to RIPv1.