What DNS server address should be used as the preferred DNS server for IPv4 settings?

The preferred DNS server address of 208.67.222.222 is the correct choice because it is one of the public DNS servers operated by OpenDNS, which is known for its reliability, speed, and security features, such as phishing protection and content filtering. Using a public DNS server like this can help ensure better performance for DNS resolution and can provide additional security features that might not be present when using a DNS server configured on a local network.

The other options include various private and public DNS addresses. The address 192.168.0.1 is typically used as a default gateway for local network devices and may not provide the broader capabilities of a dedicated public DNS server. The address 8.8.8.8 is known as a Google Public DNS server and is also a valid choice. Finally, 208.67.220.123 is another address from OpenDNS, but since the question asks for a single preferred server address and cites 208.67.222.222, it serves the purpose better as a preferred server due to its specific use case.