Just a little feedback about DUS transfer coming in from an International flight. Once we got off the plane (Terminal C), it was a hike to Immigration. No escalators, lots of stairs, and didn't notice or look for elevators. Got thru Immigration, then back thru security. Don't have any liquids with you. Short walk from there to Terminal B.
It was a 2-hour connection, and no problems. We were 1/2 hour early.
My brother on the other hand with a 1 hr 20 min connection had some problems, but made his connection. His flight was 1/2 hour late. He was seated in the back of the plane and by the time he got off and to the Immigration area, it was a zoo. Then thru security and to his gate. They must have held the flight for him as it departed 15 minutes late, and he was the last person to board. Thought he was going to miss his flight. I think what saved him is that he stopped by the Airberlin transfer center, and they must have called ahead to hold up the plane. They even asked about his luggage, which also made the flight. Close call, but it worked out.