When an application communicates with the Database Engine, the application programming interfaces (APIs) exposed by the protocol layer formats the communication using a Microsoft-defined format called a tabular data stream (TDS) packet. The SQL Server Network Interface (SNI) protocol layer on both the server and client computers encapsulates the TDS packet inside a standard communication protocol, such as TCP/IP or Named Pipes. On the server side of the communication, the network libraries are part of the Database Engine. On the client side, the network libraries are part of the SQL Native Client. The configuration of the client and the instance of SQL Server determine which protocol is used. SQL Server can be configured to support multiple protocols simultaneously, coming from different clients. Each client connects to SQL Server with a single protocol. If the client program does not know which protocols SQL Server is listening on, you can configure the client to attempt multiple protocols sequentially. The following protocols are available:
Shared Memory The simplest protocol to use, with no configurable settings. Clients using the Shared Memory protocol can connect only to a SQL Server instance running on the same computer, so this protocol is not useful for most database activity. Clients using MDAC 2.8 or earlier cannot use the Shared Memory protocol. If such a connection is attempted, the client is switched to the Named Pipes protocol.
Named Pipes A protocol developed for local area networks (LANs). A portion of memory is used by one process to pass information to another process, so that the output of one is the input of the other. The second process can be local (on the same computer as the first) or remote (on a networked computer).
TCP/IP The most widely used protocol over the Internet. TCP/IP can communicate across interconnected networks of computers with diverse hardware architectures and operating systems. It includes standards for routing network traffic and offers advanced security features. Enabling SQL Server to use TCP/IP requires the most configuration effort, but most networked computers are already properly configured.
Virtual Interface Adapter (VIA) A protocol that works with VIA hardware. This is a specialized protocol; configuration details are available from your hardware vendor.