​The Layer2 Business Data List Connector is licensed on a per SharePoint server base. That means:

• A license is required for every SharePoint server.
• There are no additional user CALs required.
• All web frontend server (WFE) have to be licensed.
• No license is required for SharePoint infrastructure servers, e.g. for index, SQL or search server.
• Application servers (APP) have to be licensed in case of SharePoint timer jobs are used, e.g. for using BDLC background update.
• The CA server (if any) has to be licensed in many cases, because it's a WFE by default (it renders the CA). In some cases timer jobs are also executed there (depending on configuration).
• The license price is per year.