The network reachability module maps and dynamically tracks network reachability of network addresses and/or devices. The network reachability module can map and dynamically track network reachability of a response-orchestrator engine, via communicating and cooperating with the response-orchestrator engine. The network reachability module has a tracking module to 1) monitor network traffic and 2) keep a list of known devices and/or known subnets on the network, which is dynamically tracked and updated as previously unknown devices and subnets on the network are detected. A trigger module generates a spoofed transmission and/or response communication, supported by a network protocol used by the network. The spoofed transmission and/or response communication can be used to map network reachability of i) network devices, ii) network addresses, and iii) any combination of both, which either 1) can receive or 2) cannot receive protocol communications from a host for the network reachability module in the network.