Systems, methods, and related technologies for a risk driven planning and simulation tool for a computer network are described. A security risk is determined for each of a plurality of devices on a network. A network traffic map is presented to a display. The network traffic map shows network traffic between the plurality of devices and the security risk for each of the plurality of devices. Segmentation of one or more of the plurality of devices on the network is simulated and presented to the display with updates to the network traffic or updates to the security risk of some of the devices on the network.