SQL Connection Error: System.Data.SqlClient.SqlException (0x80131904)

I am seeing this in several situations and it is intermittent in our web based application connecting to SQL 2008 R2 serve back end. Users are coming across a point 2 point connection and seeing this on and off. Thought it was bandwidth issues until I started seeing it on terminal servers that are on the same core switch as this SQL server. I have checked remote connection enabled, Port 1433 is set correctly in Configuration for TCP/IP and the only thing I see that could be a cause is the timeout setting is set to 100000 in the remote connections rather than unlimited.

The error is

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: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) --->

System.ComponentModel.Win32Exception (0x80004005): The network path was not found at

System.Data.SqlClient.SqlInternalConnection.OnError(SqlException
exception, Boolean breakConnection, Action`1 wrapCloseInAction) at
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject
stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) at
System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo,
SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout,
Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean
integratedSecurity, Boolean withFailover) at
System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo
serverInfo, String newPassword, SecureString newSecurePassword,
Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, Boolean
withFailover) at
System.Data.SqlClient.SqlInternalConnectionTds.LoginNoFailover(ServerInfo
serverInfo, String newPassword, SecureString newSecurePassword,
Boolean redirectedUserInstance, SqlConnectionString connectionOptions,
SqlCredential credential, TimeoutTimer timeout) at
System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(TimeoutTimer
timeout, SqlConnectionString connectionOptions, SqlCredential
credential, String newPassword, SecureString newSecurePassword,
Boolean redirectedUserInstance) at
System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity
identity, SqlConnectionString connectionOptions, SqlCredential
credential, Object providerInfo, String newPassword, SecureString
newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString
userConnectionOptions, SessionData reconnectSessionData) 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.ProviderBase.DbConnectionClosed.TryOpenConnection(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() at
System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.<>c__DisplayClass1.b__0()
at
System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1
operation) at
System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Action
operation) at
System.Data.Entity.Core.EntityClient.EntityConnection.Open()
ClientConnectionId:00000000-0000-0000-0000-000000000000

i had the same issue. go to Sql Server Configuration management->SQL Server network config->protocols for 'servername' and check named pipes is enabled.

I had the same issue.

Make sure that In SQL Server configuration --> SQL Server Services --> SQL Server Agent is enable

This solved my problem

Check these steps.

go to Sql Server Configuration management->SQL Server network config->protocols for 'servername' and check TCP/IP is enabled.
Open SSMS in run, and check you are able to login to server using specfied username/password and/or using windows authentication.
repeat step 1 for SQL native client config also

Check you routes, the update on 9/28/2014 impacted us. We had to adjust our older servers and add new routes. Here is the article http://www.rackspace.com/knowledge_center/article/updating-servicenet-routes-on-cloud-servers-created-before-june-3-2013

lmoglia

See my post here

How are you? I had the same problem while i was trying connect to MSSQL Server remotely using jdbc (dbeaver on debian).

After a while, i found out that my firewall configuration was not correctly. So maybe it could help you!

Configure the firewall to allow network traffic that is related to SQL Server and to the SQL Server Browser service.

Four exceptions must be configured in Windows Firewall to allow access to SQL Server:

A port exception for TCP Port 1433. In the New Inbound Rule Wizard dialog, use the following information to create a port exception: Select Port Select TCP and specify port 1433 Allow the connection Choose all three profiles (Domain, Private & Public) Name the rule “SQL – TCP 1433″ A port exception for UDP Port 1434. Click New Rule again and use the following information to create another port exception: Select Port Select UDP and specify port 1434 Allow the connection Choose all three profiles (Domain, Private & Public) Name the rule “SQL – UDP 1434 A program exception for sqlservr.exe. Click New Rule again and use the following information to create a program exception: Select Program Click Browse to select ‘sqlservr.exe’ at this location: [C:\Program Files\Microsoft SQL Server\MSSQL11.\MSSQL\Binn\sqlservr.exe] where is the name of your SQL instance. Allow the connection Choose all three profiles (Domain, Private & Public) Name the rule SQL – sqlservr.exe A program exception for sqlbrowser.exe Click New Rule again and use the following information to create another program exception: Select Program Click Browse to select sqlbrowser.exe at this location: [C:\Program Files\Microsoft SQL Server\90\Shared\sqlbrowser.exe]. Allow the connection Choose all three profiles (Domain, Private & Public) Name the rule SQL - sqlbrowser.exe

Source: http://blog.citrix24.com/configure-sql-express-to-accept-remote-connections/

Anyone who has this error, especially on Azure, try adding "tcp:" to the db-server-name in your connection string in your application. This forces the sql client to communicate with the db using tcp. I'm assuming the connection is UDP by default and there can be intermittent connection issues

来源：https://stackoverflow.com/questions/26135346/sql-connection-error-system-data-sqlclient-sqlexception-0x80131904

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