Product Master can have both Internal as well as external number ranges.
[ spro -> IMG -> Cross Application Components -> SAP Product -> Settings for Product Type -> Number Assignment ]
Since Products are normally imported from ECC or MDM or other external systems, the concept of number ranges has very little significance when it comes to product master ( This might seem very different for students in SAP SD training, who have learnt that material master number ranges are important ). In fact with SAP CRM Products, there could be 2 products with the same number or name and this is pretty much allowed by the system. There are other parameters like product type, Source system etc the combination of which makes up a unique product which will be discussed in the class. You can get some more information on this by understand the concept of SAP GUID more.
Double click on the product type to view the settings behind it.
The different options available under external number assignments are used under different circumstances – Some while transferring data from external systems and some in case when CRM is the master system for the products ( For example, Service or Warranty )
Also, the number range of a material can be external OR internal just like the way material numbers are created in ECC. If you specify a numeric or alphanumeric id, the system respects it. If you do NOT specify a material number/product number, then the system takes it from the internal number range assignment by default. The actual internal range assignments are right underneath by product type.