Method and system for verifying correctness of networking aspects of an Information Technology (IT) system that includes a host network of hosts. The hosts include servers and firewalls. A firewall connectivity indication of whether the host network includes an isolated firewall or a cross-zone connected firewall is determined. Determining for each host whether the host is isolated from a communication network to which the IT system is connected determines whether isolated network segments exit within the host network. For each host determined to be isolated from the communication network, the method identifies all network segments of the host network to which each host is connected, determines the unique network segments of the identified network segments, and designates the unique network segments as a set of isolated network segments. The firewall connectivity indication and the set of isolated network segments are stored in a storage medium of a computer system.