Configure a listener for an Always On availability group
This topic describes how to create or configure a single availability group listener for an Always On availability group by using SQL Server Management Studio, Transact-SQL, or PowerShell in SQL Server 2017.
To create the first availability group listener of an availability group, we strongly recommend that you use SQL Server Management Studio, Transact-SQL, or SQL Server PowerShell. Avoid creating a listener directly in the WSFC cluster except when necessary, for example, to create an additional listener.
Does a Listener Exist for this Availability Group Already?
To determine whether a listener already exists for the availability group
If a listener already exists and you want to create an additional listener, see To Create An Additional Listener for an Availability Group (Optional), later in this topic.
Limitations and Restrictions
- You can create only one listener per availability group through SQL Server. Typically, each availability group requires only one listener. However, some customer scenarios require multiple listeners for one availability group. After creating a listener through SQL Server, you can use Windows PowerShell for failover clusters or the WSFC Failover Cluster Manager to create additional listeners. For more information, see To Create An Additional Listener for an Availability Group (Optional), later in this topic.
Using a static IP address is recommended, although not required, for multiple subnet configurations.
You must be connected to the server instance that hosts the primary replica.
If you are setting up an availability group listener across multiple subnets and plan to use static IP addresses, you need to get the static IP address of every subnet that hosts an availability replica for the availability group for which you are creating the listener. Usually, you will need to ask your network administrators for the static IP addresses.
Before you create your first listener, we strongly recommend that you read Always On Client Connectivity (SQL Server).
Requirements for the DNS Name of an Availability Group Listener
Each availability group listener requires a DNS host name that is unique in the domain and in NetBIOS. The DNS name is a string value. This name can contain only alphanumeric characters, dashes/hyphens (-), and underscores (_), in any order. DNS host names are case insensitive. The maximum length is 63 characters, however, in SQL Server Management Studio, the maximum length you can specify is 15 characters.
We recommend that you specify a meaningful string. For example, for an availability group named
AG1, a meaningful DNS host name would be
NetBIOS recognizes only the first 15 chars in the dns_name. If you have two WSFC clusters that are controlled by the same Active Directory and you try to create availability group listeners in both of clusters using names with more than 15 characters and an identical 15 character prefix, you will get an error reporting that the Virtual Network Name resource could not be brought online. For information about prefix naming rules for DNS names, see Assigning Domain Names.
|The cluster object name (CNO) of WSFC cluster that is hosting the availability group must have Create Computer objects permission.
In Active Directory, a CNO by default does not have Create Computer objects permission explicitly and can create 10 virtual computer objects (VCOs). After 10 VCOs are created, the creation of additional VCOs will fail. You can avoid this by granting the permission explicitly to the WSFC cluster's CNO. Note that VCOs for availability groups that you have deleted are not automatically deleted in Active Directory and count against your 10 VCO default limit unless they are manually deleted.
Note: In some organizations, the security policy prohibits granting Create Computer objects permission to individual user accounts.
|Steps for configuring the account for the person who installs the cluster in Failover Cluster Step-by-Step Guide: Configuring Accounts in Active Directory
Steps for prestaging the cluster name account in Failover Cluster Step-by-Step Guide: Configuring Accounts in Active Directory
|If your organization requires that you prestage the computer account for a listener virtual network name, you will need membership in the Account Operator group or your domain administrator's assistance.||Steps for prestaging an account for a clustered service or application in Failover Cluster Step-by-Step Guide: Configuring Accounts in Active Directory.|
Generally, it is simplest not to prestage the computer account for a listener virtual network name. If you can, let the account to be created and configured automatically when you run the WSFC High Availability wizard.
SQL Server Permissions
|To create an availability group listener||Requires membership in the sysadmin fixed server role and either CREATE AVAILABILITY GROUP server permission, ALTER ANY AVAILABILITY GROUP permission, or CONTROL SERVER permission.|
|To modify an existing availability group listener||Requires ALTER AVAILABILITY GROUP permission on the availability group, CONTROL AVAILABILITY GROUP permission, ALTER ANY AVAILABILITY GROUP permission, or CONTROL SERVER permission.|
Using SQL Server Management Studio
The New Availability Group wizard supports creation of the listener for a new availability group.
To create or configure an availability group listener
In Object Explorer, connect to the server instance that hosts the primary replica of the availability group, and click the server name to expand the server tree.
Expand the Always On High Availability node and the Availability Groups node.
Click the availability group whose listener you want to configure, and choose one of the following alternatives:
To create a listener, right-click the Availability group Listeners node, and select the New Listener command. This opens the New Availability Group Listener dialog box. For more information, see Add Availability Group Listener (Dialog Box), later in this topic.
To change the port number of an existing listener, expand the Availability group Listeners node, right-click the listener, and select the Properties command. Enter the new port number into the Port field, and click OK.
New Availability Group Listener (Dialog Box)
Listener DNS Name
Specifies the DNS host name of the availability group listener. The DNS name is a string must be unique in the domain and in NetBIOS. This name can contain only alphanumeric characters, dashes (-), and hyphens (_), in any order. DNS host names are case insensitive. The maximum length is 15 characters.
For more information, see Requirements for the DNS Name of an Availability Group Listener, earlier in this topic.
The TCP port used by this listener.
Indicates the TCP protocol used by the listener, one of:
The listener will us a dynamic IP address that is assigned by a server running the Dynamic Host Configuration Protocol (DHCP). DHCP is limited to a single subnet.
We do not recommend DHCP in production environment. If there is a down time and the DHCP IP lease expires, extra time is required to register the new DHCP network IP address that is associated with the listener DNS name and impact the client connectivity. However, DHCP is good for setting up your development and testing environment to verify basic functions of availability groups and for integration with your applications.
The listener will use one or more static IP addresses. Additional IP addresses are optional. To create an availability group listener across multiple subnets, for each subnet you must specify a static IP address in the listener configuration. Contact your network administrator to get these static IP addresses.
If you select Static IP a subnet grid appears below the Network Mode field. This grid displays information about each subnet that can be accessed by this availability group listener. This grid is empty until you add a static IP address by clicking Add.
The columns are as follows:
Displays the identifier of each subnet that you add to the availability group listener.
Displays the IP address of a given subnet. For a given subnet, the IP address is either an IPv4 address or an IPv6 address.
Click to add to add a static IP address to a selected subnet or to another subnet for this listener. This opens the Add IP Address dialog box. For more information, see the Add IP Address Dialog Box (SQL Server Management Studio) help topic.
Click to remove the selected subnet from this listener.
Click to create the specified availability group listener.
To create or configure an availability group listener
Connect to the server instance that hosts the primary replica.
The following example adds an availability group listener to an existing availability group named
MyAg2. A unique DNS name,
MyAg2ListenerIvP6, is specified for this listener. The two replicas are on different subnets, so , as recommended, the listener uses static IP addresses. For each of the two availability replicas, the WITH IP clause specifies a static IP address,
2001:4898:f0:f00f::cf3c and 2001:4898:e0:f213::4ce2, which use the IPv6 format. This example also specifies uses the optional PORT argument to specify port
60173as the listener port.
ALTER AVAILABILITY GROUP MyAg2 ADD LISTENER 'MyAg2ListenerIvP6' ( WITH IP ( ('2001:db88:f0:f00f::cf3c'),('2001:4898:e0:f213::4ce2') ) , PORT = 60173 ); GO
To create or configure an availability group listener
Change directory (cd) to the server instance that hosts the primary replica.
To create or modify an availability group listener use one of the following cmdlets:
Creates a new availability group listener and attaches it to an existing availability group.
For example, the following New-SqlAvailabilityGroupListener command creates an availability group listener named
MyListenerfor the availability group
MyAg. This listener will use the IPv4 address passed to the -StaticIp parameter as its virtual IP address.
New-SqlAvailabilityGroupListener -Name MyListener ` -StaticIp '192.168.3.1/255.255.252.0' ` -Path SQLSERVER:\Sql\Computer\Instance\AvailabilityGroups\MyAg
Modifies the port setting on an existing availability group listener.
For example, the following Set-SqlAvailabilityGroupListener command sets the port number for the availability group listener named
1535. This port is used to listen for connections to the listener.
Set-SqlAvailabilityGroupListener -Port 1535 ` -Path SQLSERVER:\Sql\PrimaryServer\InstanceName\AvailabilityGroups\MyAg\AGListeners\MyListener
Adds a static IP address to an existing availability group listener configuration. The IP address can be an IPv4 address with subnet, or an IPv6 address.
For example, the following Add-SqlAGListenerstaticIp command adds a static IPv4 address to the availability group listener
MyListeneron the availability group
MyAg. This IPv6 address serves as the virtual IP address of the listener on the subnet
255.255.252.0. If the availability group spans multiple subnets, you should add a static IP address for each subnet to the listener.
$path = "SQLSERVER:\SQL\PrimaryServer\InstanceName\AvailabilityGroups\MyAg\AGListeners\ MyListener" ` Add-SqlAGListenerstaticIp -Path $path ` -StaticIp "2001:0db8:85a3:0000:0000:8a2e:0370:7334"
To view the syntax of a cmdlet, use the Get-Help cmdlet in the SQL Server PowerShell environment. For more information, see Get Help SQL Server PowerShell.
To set up and use the SQL Server PowerShell provider
Failure to Create An Availability Group Listener Because of Active Directory Quotas
The creation of a new availability group listener may fail upon creation because you have reached an Active Directory quota for the participating cluster node machine account. For more information, see the following articles:
Follow-up: After Creating an Availability Group Listener
MultiSubnetFailover Keyword and Associated Features
MultiSubnetFailover is a new connection string keyword used to enable faster failover with Always On Availability Groups and Always On Failover Cluster Instances in SQL Server 2012. The following three sub-features are enabled when
MultiSubnetFailover=True is set in connection string:
Faster multi-subnet failover to a multi-subnet listener for an Always On Availability Group or Failover Cluster Instances.
Faster single subnet failover to a single subnet listener for an Always On Availability Group or Failover Cluster Instances.
- This feature is used when connecting to a listener that has a single IP in a single subnet. This performs more aggressive TCP connection retries to speed up single subnet failovers.
Named instance resolution to a multi-subnet Always On Failover Cluster Instance.
- This is to add named instance resolution support for an Always On Failover Cluster Instances with multiple subnet endpoints.
MultiSubnetFailover=True Not Supported by NET Framework 3.5 or OLEDB
Issue: If your Availability Group or Failover Cluster Instance has a listener name (known as the network name or Client Access Point in the WSFC Cluster Manager) depending on multiple IP addresses from different subnets, and you are using either ADO.NET with .NET Framework 3.5SP1 or SQL Native Client 11.0 OLEDB, potentially 50% of your client-connection requests to the availability group listener will hit a connection timeout.
Workarounds: We recommend that you do one of the following tasks.
If do not have the permission to manipulate cluster resources, change your connection timeout to 30 seconds (this value results in a 20-second TCP timeout period plus a 10-second buffer).
Pros: If a cross-subnet failover occurs, client recovery time is short.
Cons: Half of the client connections will take more than 20 seconds
If you have the permission to manipulate cluster resources, the more recommended approach is to set the network name of your availability group listener to
RegisterAllProvidersIP=0. For more information, see "RegisterAllProvidersIP Setting" later in this section.
Pros: You do not need to increase your client-connection timeout value.
Cons: If a cross-subnet failover occurs, the client recovery time could be 15 minutes or longer, depending on your HostRecordTTL setting and the setting of your cross-site DNS/AD replication schedule.
When you use SQL Server Management Studio, Transact-SQL, or PowerShell to create an availability group listener, the Client Access Point is created in WSFC with the RegisterAllProvidersIP property set to 1 (true). The effect of this property value depends on the client connection string, as follows:
Connection strings that set MultiSubnetFailover to true
Always On availability groups sets the RegisterAllProvidersIP property to 1 in order to reduce re-connection time after a failover for clients whose client connection strings specify
MultiSubnetFailover = True, as recommended. Note that to take advantage of the listener multi-subnet feature, your clients might require a data provider that supports the MultiSubnetFailover keyword. For information about driver support for multi-subnet failover, see Always On Client Connectivity (SQL Server).
For information about multi-subnet clustering, see SQL Server Multi-Subnet Clustering (SQL Server).
RegisterAllProvidersIP = 1, if you run the WSFC Validate a Configuration Wizard on the WSFC cluster, the wizard generates the following warning message:
"The RegisterAllProviderIP property for network name 'Name:<network_name>' is set to 1 For the current cluster configuration this value should be set to 0."
Please ignore this message.
Connection strings that do not set MultiSubnetFailover to true
RegisterAllProvidersIP = 1, any clients whose connection strings do not use
MultiSubnetFailover = True, will experience high latency connections. This occurs because these clients attempt connections to all IPs sequentially. In contrast, if RegisterAllProvidersIP is changed to 0, the active IP address is registered in the Client Access Point in the WSFC cluster, reducing latency for legacy clients. Therefore, if you have legacy clients that need to connect to an availability group listener and cannot use the MultiSubnetFailover property, we recommend that you change RegisterAllProvidersIP to 0.
When you create an availability group listener through the WSFC cluster (Failover Cluster Manager GUI), RegisterAllProvidersIP will be 0 (false) by default.
By default, clients cache cluster DNS records for 20 minutes. By reducing HostRecordTTL, the Time to Live (TTL), for the cached record, legacy clients may reconnect more quickly. However, reducing the HostRecordTTL setting may also result in increased traffic to the DN servers.
Sample PowerShell Script to Disable RegisterAllProvidersIP and Reduce TTL
The following PowerShell example demonstrates how to configure both the RegisterAllProvidersIP and HostRecordTTL cluster parameters for the listener resource. The DNS record will be cached for 5 minutes rather than the default 20 minutes. Modifying both cluster parameters may reduce the time to connect to the correct IP address after a failover for legacy clients that cannot use the MultiSubnetFailover parameter. Replace
yourListenerName with the name of the listener that you are changing.
Import-Module FailoverClusters Get-ClusterResource yourListenerName | Set-ClusterParameter RegisterAllProvidersIP 0 Get-ClusterResource yourListenerName|Set-ClusterParameter HostRecordTTL 300 Stop-ClusterResource yourListenerName Start-ClusterResource yourListenerName
For more information about recovery times during failover, see Client Recovery Latency During Failover.
After you create an availability group listener:
Ask your network administrator to reserve the listener's IP address for its exclusive use.
Give the listener's DNS host name to application developers to use in connection strings when requesting client connections to this availability group.
Encourage developers to update client connection strings to specify
MultiSubnetFailover = True, if possible. For information about driver support for multi-subnet failover, see Always On Client Connectivity (SQL Server).
Create an Additional Listener for an Availability Group (Optional)
After you create one listener through SQL Server, you can add an additional listener, as follows:
Create the listener using either of the following tools:
Using WSFC Failover Cluster Manager:
Add a client access point and configure the IP address.
Bring the listener online.
Add a dependency to the WSFC availability group resource.
For information about the dialog boxes and tabs of the Failover Cluster Manager, see User Interface: The Failover Cluster Manager Snap-In.
Using Windows PowerShell for failover clusters:
Use Add-ClusterResource to create a network name and the IP address resources.
Use Start-ClusterResource to start the network name resource.
Use Add-ClusterResourceDependency to set the dependency between the network name and the existing SQL Server Availability Group resource.
For information about using Windows PowerShell for failover clusters, see Overview of Server Manager Commands.
Start SQL Server listening on the new listener. After creating the additional listener, connect to the instance of SQL Server that hosts the primary replica of the availability group and use SQL Server Management Studio, Transact-SQL, or PowerShell to modify the listener port.
For more information, see How to create multiple listeners for same availability group (a SQL Server Always On team blog).
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