There is a hard limit on how long your AlwaysOn listener name can be. That is expected, what may not be expected is that the limit is mere 15 characters or less.
Yes even though the maximum length allowed for an AlwaysOn listener DNS name is 63 characters, in practice you can only specify up to 15 characters. This limit comes from the NetBIOS computer name restriction, which is 15 characters, even in the latest versions of Windows 2025. Technically, the maximum length for a NetBIOS name is 16 characters, but the 16th character is reserved for identifying the network device functionality, effectively limiting it to 15 characters.
The limit is for the name part, not the entire Fully Qualified Domain Name (FQDN), which can be up to 255 characters long.
So if you are using SSMS to create an AlwaysOn Listener, it won't even let you type in more than 15 characters:
Msg 41066, Level
16, State 0, Line 3
Msg 19476, Level 16, State 4, Line 3
The attempt to
create the network name and IP address for the listener failed.
As a last resort, you could bypass the SQL Server tools completely and create the listener through the Failover Cluster Manager tool, by adding a new resource to your Availability Group of type 'Client Access Point':
On the surface, this will work and complete successfully:
In reality, the newly added Client Access Point will not come online, and your AlwaysOn resource will show as partially failed
Is there a solution or workaround that works?
Sadly, no. Though justifiably annoying, in the Microsoft Windows world, there is no way to get around this limit. The catch-all reason given is of course - "For backward compatibility with legacy Windows Computers and Applications that may still need compatibility with NetBIOS". Even if you do not have any legacy systems, this requirement is still enforced. The Windows Failover Clustering still requires that the cluster name (the virtual computer name that you can connect to) must strictly adhere to NetBIOS naming convention. And this requirement extends to related services, such as SQL listener names for Always On Availability Groups. Bottom line: If the Windows Failover Cluster (WFC) service cannot successfully register your chosen name in the network (per NetBIOS standards), the resource will be unable to come online, even if the initial resource creation appears successful.
A potential alternative could be to install your SQL Servers in the Linux world without Windows Failover Clustering and Active Directory. I am told you could have a longer name for the AlwaysOn Listener in this environment. However, I have not tested this myself and therefore would not count it as a definitive solution. Even if it works, isn't that too much effort just to name your listener with more than 15 characters?
I ended up making a slight change in my naming convention so that the listener name would not exceed 15 characters.