Hit a strange issue this morning. I was working with one of the network guys testing out connecting to SQL behind an F5 load balancer, something I’ve done multiple times previously.

I was able to connect using SQLCMD, Invoke-SQLCmd and using a UDL source, but for some reason, every time I tried to connect using SSMS I would get an error stating that an “Index was outside the bounds of an array”.

Advanced Information for Error

A little research showed that this error cropped up when trying to connect to SQL 2012 from an earlier version of SSMS. This wasn’t the case here though, everything was SQL 2012, and I was able to connect to the server directly without any problems, it was only an error when going through the F5 VIP.

After a little work and research with the network admin we discovered that OneConnect was causing the issue. It was attempting to pool connections and was causing the problem, turning it off fixed the issue entirely.

Just something to keep an eye out for if you use F5’s to handle load balancing or DR client redirection.