The Norwegian birth number (ID) is an 11 digit personal identifier. Everyone in the National Register has a birth number. As a foreigner, you will usually be given the D number (a temporary ID number) which will become your permanent ID number when you meet the necessary criteria.
As a foreigner, the social security number you get depends on your residence permit and how long you plan to stay in Norway. There are two cases in which you may be entitled to a D number. In the first case, if you intend to stay in Norway for less than 6 months. The second situation is that you intend to stay in Norway for more than 6 months, but do not meet the criteria for being assigned a birth number.
At Tecla, we have experience with this process and can help you navigate through this.