Someone once said to me that he thought I should work as a GUI tester since I always seemed to find problems in the UI after I highlighted a problem to him that I’d found in Linux Gnome that he had never seen before after all his years working with the product. I guess there is an element of truth to that statement since I really do like clicking around and trying different things. However I suspect that my latest discovery won’t necessarily be one of those obscure problems that no-one else comes across since it is such an obvious problem and fairly easy to run into.

Whilst playing around with SQL Server 2012 (Denali) Availability groups, I discovered that there is a restriction set on the size of the listener name that you are able to enter through the GUI.

Let me demonstrate…

First I will create a new DNS host name called “readpastandfurious” which you should note is 18 characters long.

And of course there isn’t a problem creating this record since the restriction upon the size of the DNS host name is (I believe 24 characters).

Next I decide to create an Availability Group Listener via the SSMS GUI wizard and am very surprised when I can only type in 15 characters! Obviously this text field must have been programmatically restricted since by default the GUI text fields would not be limited.

My first thought was that it has been restricted on purpose perhaps for an odd NETBIOS reason -if for example NETBIOS was being used for resolution in any way in addition to DNS (daft but possible). Microsoft limits NETBIOS names to 15 characters, so this might have been a plausible explanation.

Next I decide to try and create the full 18 character availability group via T-SQL and I am a little surprised to find that it succeeded with no problems at all!

ALTER AVAILABILITY GROUP [READPAST & Furious Optimistic]
ADD LISTENER 'readpastandfurious' (WITH IP ( ('10.0.5.1','255.0.0.0') ) )

My conclusion then is that this behaviour is almost certainly a bug and was introduced by a programmer who either doesn’t understand the difference between NETBIOS and DNS or blindly assumed that 15 characters is enough?! In any event I believe this is a problem and have therefore raised a connect item for this issue here give it a vote up if you believe you might fall prey to this issue at some point in the future!