If the Sophos Firewall is utilized as an explicit proxy, which web filtering option is employed?

When the Sophos Firewall is configured to function as an explicit proxy, the web filtering option that is actively employed is a web proxy. In this setup, the firewall intercepts web traffic, primarily HTTP and HTTPS, and analyzes the content passing through it.

Using a web proxy allows the firewall to perform in-depth inspection and filtering of web traffic. This means that the device can apply various filtering policies based on the URL, content type, or even user identity. Web proxies can cache frequently accessed content, enhancing performance, while also offering detailed reporting and logging capabilities for network administrators.

The other options, while they relate to different types of filtering, do not accurately describe the main mechanism used when the Sophos Firewall operates as an explicit proxy. DNS filtering typically blocks or allows domains based on DNS queries, URL filtering is a subset of web filtering that focuses on specific web addresses, and IP filtering involves controlling access based on the source or destination IP addresses rather than content. Hence, the most appropriate answer in the context of explicit proxy use is the web proxy.