I don't know.
The single best answer to any interview question is "I don't know." Granted, there are those questions that you absolutely must know; but for those you don't or for those you can skirt "I don't know" followed by a quick "Here's what I'd do..." opens the door for you to do what the interviewer really wants you to do: Show them how you work.
A classic interview is about what you've done, a short review of your accomplishments, dates of employment, best boss, worst boss, blah, blah, blah. What the interviewer really wants to know (or at least should...) is what you'll do and how you'll do it. People prefer to hire the familiar, that's why they call their former colleagues and friends first; they already know what to expect. It's your job to find the opportunity to demonstrate how you'll work -- what tools and resources you'll be using, how you communicate and involve other departments and resources and your ability to manage teams, budgets and time.
Look for the opportunity or create one. Do some homework on your potential employer and show up with the intention of demonstrating how you'd overcome a particular obstacle, task or solve a problem you know they've been faced with. You don't have to give a full blown dog and pony show, just hit the highlights before you give away too much free consulting.
You'll also establish trust because you're willing to be vulnerable and honest. The interviewer will become more comfortable knowing you're not there over committing or making things up as you go along. Credibility is king in gaining trust. You'll let them know you're willing to take initiative and won't be just be punching the clock. You're next challenge is even greater, "I don't know, here's what I'd do..." leads to familiarity and as we all know, familiarity breeds contentment.