A Net-Library is a network interface that is specific to a particular network interprocess communication (IPC) mechanism. SQL Server uses a common internal interface between Open Data Services, which manages its use of the network, and each Net-Library. By doing this, all network-specific considerations and calls are isolated to just that Net-Library. There may be multiple Net-Libraries loaded, one for each network IPC mechanism in use—for example, one for named pipes, another for TCP/IP sockets, another for SPX, and yet another for Banyan VINES SPP. Microsoft SQL Server uses this Net-Library abstraction layer at the server as well as the client, making it possible to simultaneously support clients on different networks. Windows NT allows multiple protocol stacks to be in use simultaneously on one system.
It is important to distinguish between the IPC mechanism and the underlying network protocol. IPC mechanisms used by SQL Server include named pipes, SPX, and Windows Sockets. Network protocols include NetBEUI, NWLink (SPX/IPX), TCP/IP, and VINES IP. Named pipes, a common IPC used in SQL Server environments, can be used over multiple network protocols (named pipes can be used efficiently over NetBEUI, NWLink SPX/IPX, and TCP/IP, all simultaneously).
Note SQL Server in other environments has traditionally supported only a single IPC mechanism, usually TCP/IP sockets, that was hard-coded directly into the network handler. All clients needed to communicate with that IPC mechanism, and nothing else, and usually only with a single network protocol.
SQL Server uses a multiprotocol networking library that will listen for incoming network connections on named pipes, a TCP/IP port, and an SPX socket. The named pipe name, TCP/IP port, and SPX socket number are usually chosen dynamically.
If you want users on the Internet to connect to your SQL Server using TCP/IP and your organization is using a firewall system to isolate the network containing the SQL Server from the rest of the Internet, ensure that SQL Server uses a particular port number for its incoming connections. By doing this, the firewall system will forward connections to that particular port number on your SQL Server.
For instructions about configuring SQL Server to listen for incoming connections, see What's New in SQL Server 6.5, available in the documentation set shipped with Microsoft SQL Server.