CALs. You have two basic ways to purchase access: CALs or an External Connector license. CALs are sold per-device/per-user or per server, and are fairly well understood. In an extranet scenario, it’s unlikely you’ll be able to manage device connections, so let’s assume you go with per-user licensing. You need a user CAL for each server a user accesses. For example, every user requires a CAL to access the WSS server. Similarly, each user requires a CAL to access the SQL server.
This is a very important point. You need Windows Server CALs for SQL Server access, even though technically the user isn’t touching the SQL Server, but rather WSS is a middleman, grabbing data from SQL on the user’s behalf. That doesn’t matter; you need the CALs. So if your SQL Server is on a separate physical or virtual instance of Windows Server, and you’re using per-user CALs, you’ll need two CALs per user! This is an economic (if not technical) reason why some organizations choose to run SQL Server on the same Windows Server system as WSS.
I’ve just described per-user licensing. But you can also choose per-server licensing, in which case you must have CALs for the maximum number of users or devices that might simultaneously access or use the software. Again, you need to do this on both the WSS front-end server and the SQL Server. It doesn’t matter that the SQL Server is not authenticating the users—it’s providing services (indirectly) to authenticated users.
External Connector. If your users are internal users with Active Directory (AD) accounts, there must be CALs (either per-user/per-device or per-server). There is no option. If they are external users—for example partners, customers, or vendors—who will authenticate in any way, then you can either provide CALs for those individuals as part of your per-user or per-server CALs, or you can use the External Connector license. The External Connector license allows an unlimited number of authenticated users, as long as those users are external. Again, you would do this for both the WSS front-end server and for the SQL Server if they’re running on separate instances of Windows Server.
Virtualization. If you’re running Windows Server inside a VM, the CALs or External Connector license must be purchased only for the physical system. For example, if you have run Windows Server (2003 or 2008) Enterprise Edition for the physical system, you can run four instances of Windows Server in VMs, and the CALs or External Connector for the physical system are valid for the four VMs.
Web EditionFinally, you can use the Web editions of Windows Server—Windows 2003 Web Edition or Windows Web Server 2008—which don’t require CALs or an External Connector license. You can’t run the storage (SQL) for WSS on that system, so you will still need CALs or an External Connector license for the box running SQL Server. If, however, your design prescribes a Web front end and a SQL back end, using the Web edition for the front end might save you some license cost.
Bottom line Do the math: You must have per-user (or per server) CALs for all internal users. You can choose per-user CALs, per-server CALs, or an External Connector license for external users, whichever is most economical. That’s the “Windows Server client license.” If SQL Server and WSS are on the same physical box (or running in licensed virtual instances on one physical box), you only need one “set” of that Windows Server client license package. If SQL Server and WSS are on separate physical boxes, then you’ll need two sets of your chosen client license solution. Microsoft makes this so easy, doesn’t it?