Always On Availiability Groups : Can't connect listener\named instance

Question

Hello.

After configuring Always On listener, use the listener to access SQL Server For a typical agl.domain.com
is normarlly work with TCP 1433 port
However, Access to AGL.domain.com[named instance] is not possible with the following error.

A network-related error or instance-specific error occurred while connecting to SQL Server. Verify that the instance name is correct and that it is configured to allow remote connections to SQL Server
(Provider : SQL Network Interface, error : 26 – An error occurred while trying to locate the specified server/instance.)

So, I checked the Network history with the wireshark and found that the connection is trying to access UDP 1433.

172.30.136 = Always on availability group listener.

Source Destination protocol info
172.30.2.131 172.30.2.136 UDP 52225 -> 1434

There is no problem with SQL connection because it can be accessed by port designation.

However, When I set up bussiness for skype, I could not proceed.
Because Skype Server tried to connect listnerFQDN/[named instance] in some connection.
This is approached by UDP 1434.

How can I fix it?

Please help me.

Answer 1

Hi @Tedd Yeom

This is (more or less) expected - UDP 1434 is the SQL Server Browser Service which is essential within the setup of communication between client and server.

Your client first asks the Browser service if an SQL Server is installed with that given server and instance name, then it asks for the dedicated port for that instance.
After everything is checked, the client can open a connection with the name and port... in your case, 1433.

But from a security and best practice point of view, it is not recommended to use TCP/1433 for all those listeners (node1, node2, AGL).

You should check this documentation to configure your network/firewall accordingly.
https://learn.microsoft.com/en-us/sql/sql-server/install/configure-the-windows-firewall-to-allow-sql-server-access?view=sql-server-ver16

I hope my answer is helpful to you,

Your
Bjoern Peters

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Answer 2

Thank you for your answer.

This issue was resolved when the source server opened UDP Dynamic Port.

Thank you.
Best regards.