I'm currently in Germany with a type D internship visa that covers the length of my stay (validity dates from arrival to departure, with duration of stay listed as XX).
If it makes any difference, the remarks section on my visa says:
Praktikum nach § 15 Nr. 5 Beschv bei [COMPANY NAME] in [PLACE]
Aufenthaltsdauer entspricht Gültigkeit
I've registered/have insurance/etc. I'm just wondering if getting a residence permit is mandatory.