Many clients don’t know where to start looking at an enterprise network. Finding every nook and cranny of an organization might be beyond the scope of most mortals. Using tools like fierce to do DNS enumeration and My IP Neighbors on each IP you find. Building custom dictionary files for a company can help you find all kinds of interesting spots in the organization. If you aren’t paying attention to the rest of your network and you are only focusing on the front door, chances are you are already owned.”]
Source: https://www.darkreading.com/attacks-breaches/navigating-the-c-of-network-discovery