A good exercise for any security admin is to map your security domains or zones. The idea is that a map of the inputs and outputs of your organization's data pathways will give you a clearer idea of the users, gateways, systems, and data that you are trying to secure. Unless you know about it, it's impossible to secure it. And, as the saying goes, a problem well defined is a problem half-solved.
Start with all of the ways that people can enter your environment: LAN, WAN, VPNs, Terminal Server, Citrix, RDP, Internet, wireless, smartphones, BlackBerrys, FTP, Telnet, point-to-point circuits, and so on. Then tie these entry points to all the user types: employees, consultants, business partners, remote employees, visitors, guests, vendors, business partners, auditors. Don't forget anonymous users if you have public Web sites and other non-authenticated assets. Save one big placeholder for outsiders, intruders, and unauthorized users.
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Next, define all the places where your data resides, including file servers, Web servers, database servers, SharePoint servers, laptops, mobile computers, smartphones, SANs, NASes, midrange computers, mainframe computers, offline storage, tapes, and USB keys. Classify the different data repositories with basic data classification levels. If one bit of data is high business impact (HBI), then the whole server or database is HBI.
Now here's where the graphics come in. Using Microsoft Visio or some other drawing tool, draw the lines from the people over the entry points to the data they need to access. If you manage an organization of any decent size or complexity, your diagram will look as complicated and convoluted as any you have ever seen in your life. I've seen Visio diagrams of this roll out on plotter paper reaching several feet in each direction.
This, my friends, is the environment you are being asked to manage and protect. If this is your first time trying to do this exercise, think about how you were ever able to defend your environment without this big-picture look. Isn't it all much clearer now?
To defend appropriately, you must create virtual security domains that keep disparate roles from connecting to entry points and data sets that they should not access. How you accomplish it is different for each organization -- indeed, it's different for each entry point, user type, data repository, and data classification.