A network role is computer software, hardware or a device that serves one or more other users, hardware and devices. For example, a network fax server is a network role, because it is accessed from the network and serves many people as opposed to a regular analog fax that may serve multiple users but it's not accessible from the network.
This chapter covers various network roles, such as e-mail servers, DNS servers, Web servers and more. Each network role uses one or more protocols. For some protocols it's important to go over their inner workings in order to better understand their security problems; for others, it may be unimportant for the discussion, it may be very complex, or it may fill a book of its own and therefore be out of scope. An important thing to remember is that not all network roles are Internet related, but they do carry security risks that need to be considered.
In this chapter we may refer to some other network terminology or applications, such as the following:
Not every corporate user is computer savvy. About a year ago, a client called one of the authors telling him his computer didn't work anymore. A few seconds after asking the client a few questions to try to pinpoint what went wrong, it all became clear in his response: "I opened an e-mail attachment, and my antivirus program asked me something.Without really reading it, I clicked Yes." (The client is a licensed acupuncturist and not a computer specialist, as you may have guessed.) "You opened a virus," the author said. "Why did you do that?" Of course, his answer didn't prevent this author from reinstalling the client's computer and charging him for the labor.
An end user may consider e-mail as a means to an end (for example, he uses it to communicate with other Internet users); however, as IT pros, we know it's not that simple—e-mails harbor spam, viruses, hackers, eavesdroppers and more. One single misconfiguration can spell bankruptcy for the firm we work for (or own).