Map this dude !

A complete vision of the network comes through its mapping, far before the pen-test process. Mapping is about cartography : where am I, where is my destination and what are the ways to reach it. In the meantime, I want to know what is the neibourghood made of, and what are the best places to visit.

Well, Nmap can do it for you.

Nmap ("Network Mapper") is a free and open source (license) utility for network exploration or security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap runs on all major computer operating systems, and both console and graphical versions are available.