1. Mapping the network

First of all, the intruder needs to get an idea of what he's about to attack in order to select his targets. From his point of view, the network he wants to attack is no more than a subnet, with only a certain number of addresses in use. While the intruder can exploit information provided by public services such as the Domain Name Service (DNS) to obtain a few addresses that are definitely in use, he can't be sure of the rest, so he has to find the information himself. This can be done by scanning the target network.