Explanation
The most effective security control to keep a company's physical perimeter protected against intrusions leveraged by social-engineering techniques is employee training. Employee training is a process of educating and raising awareness among staff members about security policies, procedures, and best practices. Employee training can help prevent social-engineering attacks, which are attempts to manipulate or deceive people into revealing sensitive information or granting unauthorized access to resources. Social-engineering techniques can include phishing, impersonation, tailgating, dumpster diving, or baiting. References: CompTIA Network+ N10-008 Certification Study Guide, page 343; The Official CompTIA Network+ Student Guide (Exam N10-008), page 13-8.

Explanation
Installing cameras in the server room is the best solution to identify who is responsible for the equipment being moved and misplaced. Cameras provide a way to monitor the server room in real time and can be used to identify suspicious activity. Additionally, they provide a way to review past activity and allow you to review footage to determine who may be responsible for the misplacement of equipment.

Explanation
NS stands for Name Server, and it is a DNS record that specifies which servers are authoritative for a domain.
The registrar is the entity that manages the domain registration and delegation, and it maintains the NS records for each domain. To change where the outside DNS records are hosted, the network administrator needs to change the NS records at the registrar to point to the new DNS servers that will host the outside DNS records.
References:
DNS Record Types - N10-008 CompTIA Network+ : 1.61
CompTIA Network+ N10-008 Cert Guide, page 1472

Explanation
netstat -a is a command that displays information about active TCP connections and listening ports on a system. A network administrator can use netstat -a to check if the database engine is listening on a certain port, as well as verify if there are any connections established to or from that port. References:
https://www.comptia.org/blog/what-is-netstat

Explanation
TTL (Time To Live) should be adjusted to address the issue of some visitors being unable to access the website after the A record was updated. TTL is a value that specifies how long a DNS record should be cached by DNS servers and clients before it expires and needs to be refreshed. If the TTL is too high, some DNS servers and clients may still use the old A record that points to the previous IP address of the website, resulting in connection failures. By lowering the TTL, the DNS servers and clients will update their cache more frequently and use the new A record that points to the current IP address of the website. References:
https://www.cloudflare.com/learning/dns/dns-records/dns-ttl/