Both PROFINET and PROFIBUS devices have unique Ident (ID) numbers allocated to them to assist with engineering, identification and other issues.
An ID allows devices connected to the bus to be identified with a minimum amount of protocol overhead. In addition, the ID number is used to archive files which contain information on device features and configuration (i.e. GSD or GSDML files).

The Device Identification for PROFINET IO consists of a company key (Vendor_ID) and a manufacturer-specific key (Device_ID). The Vendor_ID is assigned uniquely to a company. The Device_ID can be defined by the manufacturer specifically for the device. PI provides the schemes and the GSDML specification required to create a GSD-File.

How do I get a vendor ID and what is a device ID?

All PROFINET components have two associated IDs: A Vendor ID and a Device ID. Device manufacturer must obtain a Vendor ID and define a Device ID before testing since both IDs are included in the GSD file.

Vendor IDs are unique, and therefore managed and assigned by PI to each company. Device manufacturers can obtain their PROFINET Vendor ID at no charge by sending an email to: certification(at)profibus(dot)com. Vendor IDs are the same for PROFIBUS and PROFINET. If a device manufacturer already has a Vendor ID for PROFIBUS, there is no need to request a new one for PROFINET.
The current Manufacturer (Vendor) ID table can be viewed here: https://www.profibus.com/IM/Man_ID_Table.xml 

The Device ID is chosen and managed by the device manufacturer. Each device should have a unique Device ID specifically for the device. GSDML Technical Specification fordocument in the PROFINET Test Bundle contains details about Device ID formatting.

An Device Ident Number (ID number) is required for all PROFIBUS devices using PROFIBUS DP communication (except Master Class 2 devices).
Manufacturers must register each device type with PI and get either a manufacturer and/or profile specific Device ID number. The Device ID number is not a serial number. The value range is 0001 Hex to FFFE Hex.
As soon as an ID number for a device type has been assigned to a manufacturer, this number can be used for each manufactured device of this type without renewed registration. If the device is modified technically, it remains associated with the device type only if it is still possible to describe the parameters, modules and options (e.g. modular I/O devices) in a single GSD file.

PROFIBUS Nutzerorganisation e.V. handles the registration of PROFIBUS devices on behalf of PI.
 

https://www.profibus.com/download/registration-form-profibus-device

I&M (Identification and Maintenance) Functions were created to help manage devices more easily. They are based on Ident Numbers.

I&M-enabled devices internally manage a profile ID, a device ID and a manufacturer and access www.profibus.com using an engineering tool to locate relevant files, download them and save them locally. The tables aid in the different life cycle phases of a product, such as project planning, commissioning, parameter setting, diagnostics, repair, firmware update, asset management, and audit trailing. They are made available in machine-readable form (XML document) and in human-readable form (HTML document).

Information about the features of a device and its use as well as information about the manufacturer is available. If an inquiry from an end user occurs, the transmitted manufacturer ID is used to filter out the information stored in the table and transmit it to the tool of the end user.

Since the information is available online and not permanently stored in the device, this ensures that information is always up-to-date. For example, if the contact address of a manufacturer changes, the new information is immediately available.
 

• Manufacturer ID (= Vendor ID) table here more
• Profile ID (=API) table here more

If you do not have a manufacturer ID / vendor ID yet, you can request one by sending an e-mail to certification(at)profibus(dot)com. To change your company information please send an e-mail to certification(at)profibus(dot)com.