Troubleshoot connecting to the SQL Server Database Engine
Applies to: SQL Server (all supported versions)
This article lists troubleshooting techniques to use when you can't connect to an instance of the SQL Server Database Engine on a single server.
These steps aren't in the order of the most likely problems which you probably already tried. These steps are in order of the most basic problems to more complex problems. These steps assume that you're connecting to SQL Server instance from another computer by using the TCP/IP protocol, which is the most common situation.
These instructions are useful when troubleshooting the "Connect to Server" error, which can be
Error Number: 11001 (or 53), Severity: 20, State: 0. The following is an example of an error message:
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) (Microsoft SQL Server, Error: 53)
(provider: TCP Provider, error: 0 - No such host is known.) (Microsoft SQL Server, Error: 11001)
This error usually means that the client can't find the SQL Server instance. This normally happens when at least one of the following problems exists:
- The name of the computer hosting the SQL Server
- Instance doesn't resolve the correct IP
- The TCP port number isn't specified correctly
An interactive troubleshooting page is available from Microsoft Customer Support Services at Solving Connectivity errors to SQL Server.
- This topic doesn't include information about SSPI errors. For SSPI errors, see How to troubleshoot the "can't generate SSPI context" error message.
- This topic doesn't include information about Kerberos errors. For help, see Microsoft Kerberos Configuration Manager for SQL Server.
- This topic doesn't include information about Azure SQL Database connectivity. For help, see Troubleshooting connectivity issues with Microsoft Azure SQL Database.
Get instance name from Configuration Manger
On the server that hosts the SQL Server instance, verify the instance name. Use SQL Server Configuration Manager.
Configuration Manager is automatically installed on the computer when SQL Server is installed. Instructions on starting Configuration Manager vary slightly by version of SQL Server and Windows. For version-specific details, see SQL Server Configuration Manager.)
Sign in to the computer hosting the instance of SQL Server.
Start SQL Server Configuration Manager.
In the left pane, select SQL Server Services.
In the right pane, verify the name of the instance of the database engine.
SQL SERVER (MSSQLSERVER)denotes a default instance of SQL Server. The name of the default instance is
SQL SERVER (<instance name>)denotes a named instance of SQL Server. The name of the name instance is
<computer name>\<instance name>
Verify - the instance is running
To verify that the instance is running, in Configuration Manager look at the symbol by the SQL Server instance.
- A green arrow indicates that an instance is running.
- A red square indicates that an instance is stopped.
If the instance is stopped, right-click the instance and then click Start. The server instance starts, and the indicator becomes a green arrow.
To connect to a named instance, SQL Server Browser service must be running. In Configuration Manager, locate SQL Server Browser service and verify that it's running. If it'sn't running, start it. SQL Server Browser service isn't required for default instances.
A default instance of SQL Server doesn't require SQL Server Browser service.
Testing a local connection
Before troubleshooting a connection problem from another computer, first test your ability to connect from a client application installed locally on the computer that is running SQL Server. Connecting locally avoids issues with networks and firewalls.
This procedure uses SQL Server Management Studio. If you don't have Management Studio installed, see Download SQL Server Management Studio (SSMS). If you'ren't able to install Management Studio, you can test the connection using the
sqlcmd.exe is installed with the Database Engine. For information about
sqlcmd.exe, see sqlcmd Utility.)
Sign in to the computer where SQL Server is installed, using a login that has permission to access SQL Server. (During installation, SQL Server requires at least one login to be specified as a SQL Server Administrator. If you don't know an administrator, see Connect to SQL Server When System Administrators Are Locked Out.)
On the Start page, type SQL Server Management Studio, or on older versions of Windows on the Start menu, point to All Programs, point to Microsoft SQL Server, and then click SQL Server Management Studio.
In the Connect to Server dialog box, in the Server type box, select Database Engine. In the Authentication box, select Windows Authentication. In the Server name box, type one of the following connection types:
Connecting to Type Example Default instance
<computer name\instance name>
When connecting to a SQL Server from a client application on the same computer, the shared memory protocol is used. Shared memory is a type of local named pipe, so sometimes errors regarding pipes are encountered.
If you receive an error at this point, you need have to resolve it before proceeding. There are many possible things that could be a problem. Your login might not be authorized to connect. Your default database might be missing.
Some error messages passed to the client intentionally don't give enough information to troubleshoot the problem. This is a security feature to avoid providing an attacker with information about SQL Server. To view the complete information about the error, look in the SQL Server error log. The details are provided there.
If you receive error
18456 Login failed for user, Books Online topic MSSQLSERVER_18456 contains additional information about error codes. And Aaron Bertrand's blog has a extensive list of error codes at Troubleshooting Error 18456. You can view the error log with SSMS (if you can connect), in the Management section of the Object Explorer. Otherwise, you can view the error log with the Windows Notepad program. The default location varies with your version and can be changed during setup. The default location for SQL Server 2019 (15.x) is
C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\Log\ERRORLOG.
If you can connect using shared memory, test connecting using TCP. You can force a TCP connection by specifying
tcp:before the name. For example:
Connecting to: Type: Example: Default instance
tcp:<computer name/instance name>
If you can connect with shared memory but not TCP, then you must fix the TCP problem. The most likely issue is that TCP isn't enabled. To enable TCP, See the Enable protocols steps above.
If your goal is to connect with an account other than an administrator account, once you can connect as an administrator, try the connection again using the Windows Authentication login or the SQL Server Authentication login that the client application is using.
Get the IP address of the server
Get the IP Address of the computer hosting the instance of SQL Server.
- On the Start menu, click Run. In the Run window, type cmd, and then click OK.
- In the command prompt window, type
ipconfigand then press enter. Make a note of the IPv4 Address and the IPv6 Address.
SQL Server can connect using the either IP version 4 protocol or IP version 6 protocol. Your network could allow either or both. Most people start by troubleshooting the IPv4 address. It's shorter and easier to type.
In most cases, you connect to the Database Engine from another computer using the TCP protocol.
- Using SQL Server Management Studio on the computer running SQL Server, connect to the instance of SQL Server. In Object Explorer, expand Management, expand SQL Server Logs, and then double-click the current log.
- In the Log Viewer, click the Filter button on the toolbar. In the Message contains text box, type
server is listening on, click Apply filter, and then click OK.
- A message similar to
Server is listening on [ 'any' <ipv4> 1433]should be listed.
This message indicates that this instance of SQL Server is listening on all the IP addresses on this computer (for IP version 4) and is listening to TCP port 1433. (TCP port 1433 is usually the port used by the Database Engine or a default instance of SQL Server. Only one instance of SQL Server can use a port, so if there's more than one instance of SQL Server installed, some instances must use other port numbers.) Make a note of the port number used by the SQL Server instance that you're trying to connect to.
IP address 127.0.0.1 is probably listed. It's called the loopback adapter address. Only processes on the same computer can use it to connect. It can be useful for troubleshooting, but you can't use it to connect from another computer.
In some installations of SQL Server, connecting to the Database Engine from another computer isn't enabled unless an administrator uses Configuration Manager to enable it. To enable connections from another computer:
- Open SQL Server Configuration Manager, as described earlier.
- Using Configuration Manager, in the left pane expand SQL Server Network Configuration, and then select the instance of SQL Server that you want to connect to. The right-pane lists the connection protocols available. Shared Memory is normally enabled. It can only be used from the same computer, so most installations leave Shared Memory enabled. To connect to SQL Server from another computer, you normally use TCP/IP. If TCP/IP isn't enabled, right-click TCP/IP, and then click Enable.
- If you changed the enabled setting for any protocol, restart the Database Engine. In the left pane, select SQL Server Services. In the right-pane, right-click the instance of the Database Engine, and then click Restart.
Testing TCP/IP connectivity
Connecting to SQL Server by using TCP/IP requires that Windows can establish the connection. Use the
ping tool to test TCP.
On the Start menu, click Run. In the Run window type cmd, and then click OK.
In the command prompt window, type
ping <ip address>and then the IP address of the computer that is running SQL Server. For example:
If your network is properly configured,
Reply from <IP address>followed by some additional information. If
Destination host unreachableor
Request timed out, then TCP/IP isn't correctly configured. Errors at this point could indicate a problem with the client computer, the server computer, or something about the network such as a router. To troubleshoot network problems, seeAdvanced troubleshooting for TCP/IP issues.
Next, if the ping test succeeded using the IP address, test that the computer name can be resolved to the TCP/IP address. On the client computer, in the command prompt window, type
pingand then the computer name of the computer that is running SQL Server. For example,
pingto the IP address succeeds, but
pingto the computer returns
Destination host unreachableor
Request timed outyou might have old (stale) name resolution information cached on the client computer. Type
ipconfig /flushdnsto clear the DNS (Dynamic Name Resolution) cache. Then ping the computer by name again. With the DNS cache empty, the client computer checks for the newest information about the IP address for the server computer.
If your network is properly configured,
Reply from <IP address>followed by some additional information. If you can successfully ping the server computer by IP address but receive an error such as
Destination host unreachable.or
Request timed out.when pinging by computer name, then name resolution isn't correctly configured. (For more information, see the 2006 article previously referenced, How to Troubleshoot Basic TCP/IP Problems.) Successful name resolution isn't required to connect to SQL Server, but if the computer name can't be resolved to an IP address, then connections must be made specifying the IP address. Name resolution can be fixed later.
Open a port in the firewall
By default, the Windows firewall is turned on and blocks the connections from another computer. To connect using TCP/IP from another computer, on the SQL Server computer you must configure the firewall to allow connections to the TCP port used by the Database Engine. The default instance is listening on TCP port 1433, by default. If you have named instances or if you changed the default instance port, the SQL Server TCP port may be listening on another port. See Get the SQL Server instance TCP port.
If you're connecting to a named instance or a port other than TCP port 1433, you must also open the UDP port 1434 for the SQL Server Browser service. For step-by-step instruction on opening a port in the Windows firewall, see Configure a Windows Firewall for Database Engine Access.
Test the connection
Once you can connect using TCP on the same computer, it's time to try connecting from the client computer. You could theoretically use any client application, but to avoid additional complexity, install the SQL Server Management tools on the client and make the attempt using SQL Server Management Studio.
On the client computer, using SQL Server Management Studio, attempt to connect using the IP Address and the TCP port number in the format IP address comma port number. For example,
192.168.1.101,1433. If this connection fails, then you probably have one of the following problems:
pingof the IP address doesn't work, indicating a general TCP configuration problem. Go back to the section Testing TCP/IP connectivity.
- SQL Server isn't listening on the TCP protocol. Go back to the section Enable protocols.
- SQL Server is listening on a port other than the port you specified. Go back to the section Get the TCP port number.
- The SQL Server TCP port is being blocked by the firewall. Go back to the section Open a port in the firewall.
Once you can connect using the IP address and port number, attempt to connect using the IP address without a port number. For a default instance, just use the IP address. For a named instance, use the IP address and the instance name in the format IP address backslash instance name, for example
192.168.1.101\<instance name>If this doesn't work, then you probably have one of the following problems:
- If you're connecting to the default instance, it might be listening on a port other than TCP port 1433, and the client isn't attempting to connect to the correct port number.
- If you're connecting to a named instance, the port number isn't being returned to the client.
Both of these problems are related to the SQL Server Browser service, which provides the port number to the client. The solutions are:
- Start the SQL Server Browser service. See the instructions to start browser in SQL Server Configuration Manager.
- The SQL Server Browser service is being blocked by the firewall. Open UDP port 1434 in the firewall. Go back to the section Open a port in the firewall. Make sure you're opening a UDP port, not a TCP port.
- The UDP port 1434 information is being blocked by a router. UDP communication (user datagram protocol) isn't designed to pass through routers. This keeps the network from getting filled with low-priority traffic. You can configure your router to forward UDP traffic, or you can decide to always provide the port number when you connect.
- If the client computer is using Windows 7 or Windows Server 2008, (or a more recent operating system,) the UDP traffic might be dropped by the client operating system because the response from the server is returned from a different IP address than was queried. This is a security feature blocking "loose source mapping." For more information, see the Multiple Server IP Addresses section of the Books Online topic Troubleshooting: Timeout Expired. This is an article from SQL Server 2008 R2, but the principals still apply. You can configure the client to use the correct IP address, or you can decide to always provide the port number when you connect.
Once you can connect using the IP address (or IP address and instance name for a named instance), attempt to connect using the computer name (or computer name and instance name for a named instance). Put
tcp:in front of the computer name to force a TCP/IP connection. For example, for the default instance on a computer named
tcp:ACCNT27For a named instance called
PAYROLL, on that computer use
tcp:ACCNT27\PAYROLLIf you can connect using the IP address but not using the computer name, then you have a name resolution problem. Go back to the section Testing TCP/IP connectivity, section 4.
Once you can connect using the computer name forcing TCP, attempt connecting using the computer name but not forcing TCP. For example, for a default instance use just the computer name such as
CCNT27For a named instance use the computer name and instance name like
ACCNT27\PAYROLLIf you could connect while forcing TCP, but not without forcing TCP, then the client is probably using another protocol (such as named pipes).
- On the client computer, using SQL Server Configuration Manager, in the left-pane expand SQL Native Client version Configuration, and then select Client Protocols.
- On the right-pane, Make sure TCP/IP is enabled. If TCP/IP is disabled, right-click TCP/IP and then click Enable.
- Make sure that the protocol order for TCP/IP is a smaller number that the named pipes (or VIA on older versions) protocols. Generally you should leave Shared Memory as order 1 and TCP/IP as order 2. Shared memory is only used when the client and SQL Server are running on the same computer. All enabled protocols are tried in order until one succeeds, except that shared memory is skipped when the connection isn't to the same computer.