So how do you know when to suspect DNS is causing the problem on your network?

What will be an ideal response?

Just about everything you do on an IP network depends on DNS to find the right system to talk to for whatever job the application does. E-mail clients use DNS to find their e-mail servers; FTP clients use DNS for their servers; Web browsers use DNS to find Web servers; and so on. The first clue something is wrong is generally when a user calls, saying he's getting a "server not found" error. Server not found errors look different depending on the application, but you can count on something being there that says in effect "server not found."