SqlClient Default Protocol Order

A while ago, someone came to me with a very interesting problem: basically, his .NET application was taking more than a minute to open a connection. After a quick look and some investigations, we found out that only Named Pipes was enabled on this individual’s SQL Server. Since this is a legitimate configuration, I decided to document this behavior in this post, so that, you can quickly find an answer if you face this problem.

As you know, SqlClient implements native access to SQL Server on top of SQL’s protocol layer. To establish communication between client and server both need to use the same protocol.

By default, SqlClient attempts to make the connection using the following protocol order[1]:

  1. Shared Memory
  2. TCP/IP
  3. Named Pipes

Starting from the first one, it moves to the next, failure after failure until reaching a valid one. So, if only Named Pipes is enabled on the server, the client goes through a failed Shared Memory and a failed TCP/IP (with their timeouts) before reaching the right one.

Read more: ADO.NET team blog

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