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SQL Server clients may change protocols when the client computers try to connect to an instance of SQL Server
Article ID: 328383 - View products that this article applies to.
This article was previously published under Q328383
Client computers that have Microsoft Data Access Components (MDAC) version 2.6, or later, can try multiple protocols or Interprocess Communication (IPC) mechanisms to establish connections to SQL Server.
An enhancement has been made to the client side network library, Dbnetlib.dll for MDAC version 2.6, and later. With MDAC version 2.6, and later, if multiple protocols are available, and a connection attempt with the first protocol fails, the client application immediately tries to use one of the other protocols.
By default, clients have TCP and Named Pipes as available protocols. You can manipulate the protocol ordering by using the SQL Server Client utility. The client application uses the protocols in the order specified on the client computer. The protocol order is stored at the following registry key location under the value ProtocolOrder:
If you are using SQL Server 2005, the protocol order is stored in the ProtocolOrder registry entry under the following registry subkey:
For example, if a client computer has both TCP and Named Pipes available, and the order is:
Note The client does not receive an error that indicates the first protocol failed.
If the client application uses the second protocol, and it also returns an error, an error is returned to the client.
If you make an alias by using one of the following methods, the client application uses the alias information to establish a connection to the server and does not use any additional protocols.
REFERENCESSQL Server Books Online; topic: "SQL Server Client Network utility"
Article ID: 328383 - Last Review: December 30, 2005 - Revision: 4.3