What method can be used for passive information gathering regarding an organization's network?

Using the method of examining DNS and IP block information is a valid approach for passive information gathering about an organization's network because it allows a security professional to collect essential details without actively engaging with the network or its systems. This method involves researching domain registrations and identifying IP address allocations, which can reveal insights into the organization’s infrastructure, including what domains they control and how their network is structured.

This passive approach is beneficial because it minimizes the likelihood of detection while still yielding valuable reconnaissance data. By understanding the DNS records, one can find useful information such as email servers, web servers, and other publicly accessible resources, providing a clearer picture of the organization's digital presence.

In contrast, other methods, such as interacting directly with the target systems, involve an active engagement that could alert the organization to potential reconnaissance efforts. Analyzing network traffic usually requires some level of access or intrusion to observe the communications happening within the network. Conducting interviews with employees, while potentially informative, is not a passive method and could also lead to exposing the inquirer or harm the organization's security posture.