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Timeout occurs when you connect to an Always On listener in multi-subnet environment

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This article helps you resolve the problem that occurs when you connect to a SQL Server Always On availability group listener in a multi-subnet environment.

Original product version:   SQL Server 2012 Developer, SQL Server 2012 Enterprise, SQL Server 2012 Express, SQL Server 2012 Standard, SQL Server 2012 Web, SQL Server 2012 Enterprise Core
Original KB number:   2792139

Symptoms

After you configure the availability group listener for an Always On Availability Group in Microsoft SQL Server 2012, you may be unable to ping the listener or connect to it from an application.

For example, when you try to connect to a listener of SQL Server by using SQLCMD, the connection times out. Additionally, you receive an error message that resembles the following:

Sqlcmd: Error: Microsoft SQL Native Client: Login timeout expired.

Note

These symptoms are usually intermittent, or related to failover of the availability group resource.

The following screenshot shows an example of what occurs when you try to ping the listener for the availability of aglisten. The screenshot also shows a successful connection to SQL Server by using the SQLCMD command when you include the multi-subnet failover parameter -M.

Screenshot of the Command Prompt window when you ping the listener for the availability of aglisten.

Note

You can use the SQLCMD command together with the -M parameter as shown in the screenshot to connect to the listener.

Cause

This issue occurs because your application either uses a legacy data provider that does not support the new MultiSubnetFailover parameter, or isn't configured to use this parameter.

This parameter is supported in newer versions of the SQLClient driver that is included with the .NET Framework 4 and with later versions of the .NET Framework, and is back ported to the .NET Framework 3.5.

Note

The PING command is a simple connectivity testing tool that does not support the new parameter.

Resolution

You can use one of the following resolutions as applicable to your case:

  • To resolve this situation when the data providers support the MultiSubNetFailover parameter, add the MultiSubNetFailover parameter to your connection string, and set it to true.

  • To resolve this situation when your legacy clients cannot use the MultiSubnetFailover property, you can change the listener's RegisterAllProvidersIP value to 0. To do this, run the following command from the Windows PowerShell command-line interface:

    Import-Module FailoverClusters
Get-ClusterResource <*Your listener name*>|Set-ClusterParameter RegisterAllProvidersIP 0

    Screenshot shows the output of an example of the command in Windows PowerShell.

Note

After you set the RegisterAllProvidersIP value to 0, the current online IP address must be un-registered from the DNS server and the offline IP address must be registered to the DNS server when a failover occurs. This may cause a connection delay for the next failover.

More information

When you try to connect to a listener that is defined on more than one subnet, the operation may fail if the client driver tries to connect by using one of the listener's offline IP addresses.

When a listener is created, an IP address is designated for each unique subnet that an availability group replica is hosted in. For example, if a listener is created for an availability group that has replicas that exist in two subnets, two IP addresses are defined in the listener. One address is used by an application that can connect to an instance of SQL Server in subnet 1, and the other address is used when an application connects to an instance of SQL Server in subnet 2.

Behind the scenes, the listener creates a Windows cluster Client Access Point resource. One of its properties is RegisterAllProvidersIP. When a listener is created, this is set to 1, and all the listener's IP addresses are registered in DNS server. This configuration provides reduced reconnection time for clients.

Because the DNS record contains all the IP addresses, a client that tries to connect to the listener must know how to handle this situation. The MultiSubnetFailover parameter enables the client driver to try connections in parallel to all the listener's IP addresses. Without the MultiSubnetFailover parameter, the client driver will try to connect sequentially to all IP addresses for the listener. Sequential connections may cause a long logon time or logon time-outs.

Note

The problem that is mentioned in this article also affects SharePoint environments that are configured to use an Always On Availability Group's secondary read-only replica. To resolve this issue, perform whichever of the following actions applies to your version of SharePoint:

References