Which of the following would be an example of a YANG Leaf item that is considered read-only?

A YANG Leaf item that is considered read-only refers to data that can be retrieved but not modified. The operational status of an interface falls under this category because it reflects real-time conditions such as whether an interface is up or down, its bandwidth usage, and other performance metrics. This information is typically retrieved from the device's operational state rather than being configurable by the user.

In contrast, configuration settings of a router can be modified, hence they are not read-only. Similarly, log files from a server can often be both read and potentially altered, depending on access rights, so they do not fit the read-only criteria. Access control lists (ACLs) are also configured settings that can be changed to control network traffic, rather than being purely informational in nature. Therefore, the operational status of an interface is a prime example of a YANG Leaf item that is read-only, as it serves to provide insights into the device's state without allowing for changes to that state.