Explanation
A Service-level agreement (SLA) is a document that outlines the responsibilities of a cloud service provider and the customer. It typically includes the agreed-upon availability of the cloud service provider, the expected uptime for the service, and the cost of any downtime or other service interruptions. Consulting the SLA is the best way for the management team to determine the promised availability of the cloud provider. Reference:
CompTIA Cloud+ Study Guide, 6th Edition, page 28.

Explanation
DNS poisoning is a type of attack that modifies the DNS records of a domain name to point to a malicious IP address instead of the legitimate one. This can result in users being directed to cloned websites that are stealing credentials, even if they enter the correct URL for the website. The incorrect DNS server address on the user's PC could be a sign of DNS poisoning, as the attacker could have compromised the DNS server or spoofed its response to redirect the user's queries. References: https://www.comptia.org/blog/what-is-dns-poisoning

The users are unable to navigate to websites on the internet but can access local network resources, indicating a possible DNS issue. The ping command result showing "TTL expired in transit" suggests that packets are not reaching their destination due to a DNS misconfiguration that is not resolving website names into IP addresses correctly3. A possible solution is to check and correct the DNS server settings on the network devices4.

Subinterfaces are logical divisions of a physical interface that allow a router to communicate with multiple networks using a single LAN port. Subinterfaces can have different IP addresses, VLANs, and routing protocols. They are useful for reducing the number of physical interfaces and cables needed, as well as improving network performance and security.
References:
Subinterfaces - CompTIA Network+ N10-008 Domain 1.21 - YouTube1
CompTIA Network+ Certification Exam Objectives, page 92