The disadvantages of RIP (Routing Information Protocol) include the following.
---Outdated, insecure, and slow. This is your parents' protocol. It was a thing before the Web was born.
---The more well-known problem of the 15 hop limitation in which data must travel
---Convergence time is terrible for information propagation in a network
---Metrics. It determines the number of hops from source to destination, and gives no regard to other factors when determining the best path for data to travel
---Overhead. A good example would be routing tables. These are broadcast at half-minute intervals to other routers regardless of whether the data has changed or not. It's essentially like those old cartoons where the town guard in the walled city cries out, '10 o' the clock and all is well!'.
RIPv2 introduced more security and reduced broadcast traffic, which is relevant for some available answers here.

When a network administrator observes CRC errors on a specific switchport associated with one user, the first troubleshooting step recommended is to replace the user's network cable. CRC errors are often indicative of physical layer issues such as noise, interference, or damaged cables. By replacing the network cable, the administrator can potentially resolve these errors without more drastic measures like replacing hardware components (NIC, switch, or uplink cables), which could be more costly and less effective as initial steps. This approach minimizes downtime and is a cost-effective first step in the troubleshooting process.

Tailgating is a physical security attack where an unauthorized person follows an authorized person into a restricted area without proper identification or authorization. The network administrator prevented this attack by stopping and directing the person to the security desk. Reference: CompTIA Network+ Certification Exam Objectives Version 2.0 (Exam Number: N10-006), Domain 3.0 Network Security, Objective 3.1 Compare and contrast risk-related concepts.

To prevent IP address conflicts when allocating a portion of a DHCP scope's subnet for statically assigned devices, it is recommended to use the concept of DHCP exclusion ranges. DHCP exclusion ranges allow a DHCP administrator to specify a range of IP addresses within the scope that should not be assigned to DHCP clients. This can be useful in situations where some devices on the network need to be assigned static IP addresses, as it ensures that the statically assigned addresses do not overlap with addresses assigned by the DHCP server. To set up a DHCP exclusion range, the administrator needs to specify the start and end IP addresses of the range, as well as the subnet mask. The DHCP server will then exclude the specified range of addresses from its pool of available addresses, and will not assign them to DHCP clients. By using DHCP exclusion ranges, the technician can ensure that the statically assigned addresses do not conflict with addresses assigned by the DHCP server, and can prevent IP address conflicts on the network.
Anthony Sequeira
"Another frequent configuration you might make in a DHCP implementation is to configure an exclusion range. This is a portion of the address pool that you never want leased out to clients in the network. Perhaps you have numbered your servers 192.168.1.1-192.168.1.10. Because the servers are statically configured with these addresses, you exclude these addresses from the 192.168.1.0/24 pool of addresses." Mike Meyers
"Exclusion ranges represent an IP address or range of IP addresses from the pool of addresses that are not to be given out by the DHCP server. Exclusions should be made for the static addresses manually configured on servers and router interfaces, so these IP addresses won't be offered to DHCP clients."

An access control list (ACL) is a set of rules that defines which traffic is allowed or denied on a network device, such as a router or a firewall12.
An ACL can be used to filter traffic based on various criteria, such as source or destination IP address, port number, protocol, or time of day12.
By implementing an ACL on the edge router of the network, the network administrator can block the unauthorized IP address from entering the secure part of the network every night at 8:00 pm12.
This solution would address the concerns of the network administrator, as it would prevent the unauthorized IP address from accessing the critical server or any other resource on the secure network12.
Changing the VLAN of the web server (A) or changing the server's IP address (B) would not stop the unauthorized IP address from entering the network, as it could still scan the network for other open ports or vulnerabilities12.
Instating a rule on the firewall connected to the web server (D) would only protect the web server, but not the rest of the secure network, from the unauthorized IP address12. Reference:
CompTIA Network+ N10-008 Certification Study Guide, Chapter 4: Network Operations, Section 4.3: Network Security Devices and Technologies, pp. 212-213.
Professor Messer's CompTIA N10-008 Network+ Course, Section 4.3: Network Security Devices and Technologies, Video: Access Control Lists.