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SQL server named instance connection

Hi Guys,

I am new to SQL Server Database. On several occasions, I have observed an intermittent connection failure to SQL server resulting in the following stack trace
System.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)
   at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, DbConnectionPool pool, String accessToken, Boolean applyTransientFaultHandling, SqlAuthenticationProviderManager sqlAuthProviderManager)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
   at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()
While attempting to debug this I stumbled across a blog post stating that named instance connections are initiated via the SSRP (SQL Server Resolution Protocol) using UDP. Reading the SSRP protocol specification I see no mentions of retries. This leads me to believe that loss of either the client "query" packet or the server "response" packet can lead to a named instance being unreachable when using named instances, whereas a connection to the default (unnamed) instance has no such issues. Is my understanding correct?

Thanks & Regards
Camillelola
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Answers

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    Hi @camillelola,

    Is this in relation to SQL Compare connecting to the named instance or just in general connecting to SQL Server?

    This article is useful for troubleshooting the error, I have found it normally related to the SQL Browser service being off in most cases I've seen.  The SQL Browser Service replaced SSRP from SQL Server 2005 onward.  

    As for why the default may work when the named may not, is that requests made when the browser service are off fall back to trying the default port 1433, which is what the default instance normally runs on and so it connects.

    I hope that helps!

    Kind regards,
    Alex
    Product Support Engineer | Redgate Software

    Have you visited our Help Center?
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    Hi Alex,

    Thanks for your Information it is very helpful for me. Thanks for your reply.
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