Port listener

Skip to main content This browser is no longer supported. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. Configure a DNN listener for an availability group Article06/18/2024 In this article -->Applies to: SQL Server on Azure VMWith SQL Server on Azure VMs in a single subnet, the distributed network name (DNN) routes traffic to the appropriate clustered resource. It provides an easier way to connect to an Always On availability group (AG) than the virtual network name (VNN) listener, without the need for an Azure Load Balancer.This article teaches you to configure a DNN listener to replace the VNN listener and route traffic to your availability group with SQL Server on Azure VMs for high availability and disaster recovery (HADR).For an alternative connectivity option, consider a VNN listener and Azure Load Balancer instead.OverviewA distributed network name (DNN) listener replaces the traditional virtual network name (VNN) availability group listener when used with Always On availability groups on SQL Server VMs. This negates the need for an Azure Load Balancer to route traffic, simplifying deployment, maintenance, and improving failover.Use the DNN listener to replace an existing VNN listener, or alternatively, use it in conjunction with an existing VNN listener so that your availability group has two distinct connection points - one using the VNN listener name (and port if non-default), and one using the DNN listener name and port.CautionThe routing behavior when using a DNN differs when using a VNN. Do not use port 1433. To learn more, see the Port consideration section later in this article.PrerequisitesBefore you complete the steps in this article, you should already have:SQL Server starting with either SQL Server 2019 CU8 and later, SQL Server 2017 CU25 and later, or SQL Server 2016 SP3 and later on Windows Server 2016 and later.Decided that the distributed network name is the appropriate connectivity option for your HADR solution.Configured your Always On availability group.Installed the latest version of PowerShell.Identified the unique port that you will use for the DNN listener. The port used for a DNN listener must be unique across all replicas of the availability group or failover cluster instance. No other connection can share the same port.NoteIf you have multiple AGs or FCIs on the same cluster and you use either a DNN or VNN listener, then each AG or FCI needs its own independent connection point.Create scriptUse PowerShell to create the distributed network name (DNN) resource and associate it with your availability group.To do so, follow these steps:Open a text editor, such as Notepad.Copy and paste the following script:param ( [Parameter(Mandatory=$true)][string]$Ag, [Parameter(Mandatory=$true)][string]$Dns, [Parameter(Mandatory=$true)][string]$Port)Write-Host "Add a DNN listener for availability group $Ag with DNS name $Dns and port $Port"$ErrorActionPreference = "Stop"# create the DNN resource with the port as the resource nameAdd-ClusterResource -Name $Port -ResourceType "Distributed Network Name" -Group $Ag # set the DNS name of the DNN resourceGet-ClusterResource -Name $Port | Set-ClusterParameter -Name DnsName -Value $Dns # start the DNN resourceStart-ClusterResource -Name $Port$Dep = Get-ClusterResourceDependency -Resource $Agif ( $Dep.DependencyExpression

Receive operations. SEND_BUF_SIZEUse the SEND_BUF_SIZE parameter to specify buffer space for session send operations. 8.2.1 ADDRESS The protocol ADDRESS parameter’s networking parameter is in the listener.ora file. It specifies the protocol address under the DESCRIPTION parameter for one listener. Purpose Specifies a single listener protocol address in the DESCRIPTION parameter Usage Notes Use this parameter to define the protocol, the host, and the port number for the listener. Examplelistener_name= (DESCRIPTION= (ADDRESS_LIST= (ADDRESS=(PROTOCOL=tcp)(HOST=hr-server)(PORT=1521)) (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)))) 8.2.2 DESCRIPTION DESCRIPTION networking parameter of the listener.ora file contains listener protocol addresses. Purpose To contain listener protocol addresses. Example 8-2 Examplelistener_name= (DESCRIPTION= (ADDRESS_LIST= (ADDRESS=(PROTOCOL=tcp)(HOST=hr-server)(PORT=1521)) (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)))) 8.2.3 Firewall Purpose It can be set in endpoint to enable firewall functionality. 8.2.4 IP The protocol address parameter IP determine which IP address the listener listens on when a host name is specified Purpose To determine which IP address the listener listens on when a host name is specified. Usage Notes This parameter is only applicable when the HOST parameter specifies a host name. Values first Listen on the first IP address returned by the DNS resolution of the host name. If the user wants the listener to listen on the first IP to which the specified host name resolves, then the address must be qualified with (IP=first). v4_only Listen only on IPv4 addresses. v6_only Listen only on IPv6 addresses. Default This feature is disabled by default. Example listener_name= (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=rancode1-vip)(PORT=1522)(IP=v6_only)) 8.2.5 QUEUESIZE Purpose To specify the number of concurrent connection requests that the listener can accept on a TCP/IP or IPC listening endpoint (protocol address). Usage Notes The number of concurrent connection requests is dependent on the platform and listener usage scenarios. If the listener is heavily-loaded, then set the parameter to a higher number. Put this parameter at the end of the protocol address with its value set to the expected number of concurrent connection requests. Default The default number of concurrent connection requests is operating system specific. Example listener_name= (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=hr-server)(PORT=1521)(QUEUESIZE=20))) 8.2.6 RECV_BUF_SIZE Use the RECV_BUF_SIZE parameter to specify buffer space for session receive operations. Purpose To specify, in bytes, the buffer space for receive operations of

-match '\s*\((.*)\)\s*' ){$DepStr = "$($Matches.1) or [$Port]"}else{$DepStr = "[$Port]"}Write-Host "$DepStr"# add the Dependency from availability group resource to the DNN resourceSet-ClusterResourceDependency -Resource $Ag -Dependency "$DepStr"#bounce the AG resourceStop-ClusterResource -Name $AgStart-ClusterResource -Name $AgSave the script as a .ps1 file, such as add_dnn_listener.ps1.Execute scriptTo create the DNN listener, execute the script passing in parameters for the name of the availability group, listener name, and port.For example, assuming an availability group name of ag1, listener name of dnnlsnr, and listener port as 6789, follow these steps:Open a command-line interface tool, such as command prompt or PowerShell.Navigate to where you saved the .ps1 script, such as c:\Documents.Execute the script: add_dnn_listener.ps1 . For example:c:\Documents> .\add_dnn_listener.ps1 ag1 dnnlsnr 6789Verify listenerUse either SQL Server Management Studio or Transact-SQL to confirm your DNN listener is created successfully.SQL Server Management StudioExpand Availability Group Listeners in SQL Server Management Studio (SSMS) to view your DNN listener:Transact-SQLUse Transact-SQL to view the status of the DNN listener:SELECT * FROM SYS.AVAILABILITY_GROUP_LISTENERSA value of 1 for is_distributed_network_name indicates the listener is a distributed network name (DNN) listener:Update connection stringUpdate the connection string for any application that needs to connect to the DNN listener. The connection string to the DNN listener must provide the DNN port number, and specify MultiSubnetFailover=True in the connection string. If the SQL client does not support the MultiSubnetFailover=True parameter, then it is not compatible with a DNN listener.The following is an example of a connection string for listener name DNN_Listener and port 6789:DataSource=DNN_Listener,6789;MultiSubnetFailover=TrueTest failoverTest failover of the availability group to ensure functionality.To test failover, follow these steps:Connect to the DNN listener or one of the replicas by using SQL Server Management Studio (SSMS).Expand Always On Availability Group in Object Explorer.Right-click the availability group and choose Failover to open the Failover Wizard.Follow the prompts to choose a failover target and fail the availability group over to a secondary replica.Confirm the database is in a synchronized state on the new primary replica.(Optional) Fail back to the original primary, or another secondary replica.Test connectivityTest the connectivity to your DNN listener with these steps:Open SQL Server Management Studio.Connect to your DNN listener.Open a new query window and check which replica you're connected to by running SELECT @@SERVERNAME.Fail the availability group over to another replica.After a reasonable amount of time, run SELECT @@SERVERNAME to confirm your availability group is now hosted on another replica.LimitationsDNN Listeners MUST be configured with a unique port. The port cannot be shared with any other connection on any replica.The client connecting to the DNN listener must support the MultiSubnetFailover=True parameter in the connection string.There might be additional considerations when you're working with other SQL Server features and an availability group with a DNN. For more information, see AG with DNN interoperability.Port considerationsDNN listeners are designed to listen on all IP addresses, but on a specific, unique port. The DNS entry for the listener name should resolve to the addresses of all replicas in the availability group. This is done automatically with the PowerShell script provided in the Create Script section.

Since DNN listeners accept connections on all IP addresses, it is critical that the listener port be unique, and not in use by any other replica in the availability group. Since SQL Server listens on port 1433 by default, either directly or via the SQL Browser service, using port 1433 for the DNN listener is strongly discouraged.If the listener port chosen for the VNN listener is between 49,152 and 65,536 (the default dynamic port range for TCP/IP, add an exclusion for this. Doing so will prevent other systems from being dynamically assigned the same port.You can add a port exclusion with the following command:netsh int ipv4 add excludedportrange tcp startport= numberofports=1 store=persistentNext stepsOnce the availability group is deployed, consider optimizing the HADR settings for SQL Server on Azure VMs.To learn more, see:Windows Server Failover Cluster with SQL Server on Azure VMsAlways On availability groups with SQL Server on Azure VMsAlways On availability groups overview --> Feedback Additional resources In this article