There are two types of nets that fit the 2-series:
1).
This one, which hooks into the six plastic buttons mounted to the lift-able tray that conceals your battery, etc. It's fasteners are plastic, and the net has a pocket on one side. This came with my car, and from what I understand should be standard equipment from BMW AG. If it was removed, your dealer should supply one at your request.
2).
This one, which is somewhat generic, slightly larger, cheaper, and hooks to the four metal loops in the trunk area.